Citation
Hydrogen Atom Abstraction Reactivity of a Primary Fluoroalkyl Radical in Water

Material Information

Title:
Hydrogen Atom Abstraction Reactivity of a Primary Fluoroalkyl Radical in Water
Creator:
CRADLEBAUGH, JOSEPH AARON ( Author, Primary )
Copyright Date:
2008

Subjects

Subjects / Keywords:
Alkenes ( jstor )
Alkoxides ( jstor )
Atoms ( jstor )
Deuterium ( jstor )
Ethers ( jstor )
Hydrogen ( jstor )
Isotope effects ( jstor )
Kinetics ( jstor )
Sodium ( jstor )
Solvents ( jstor )

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright Joseph Aaron Cradlebaugh. Permission granted to University of Florida to digitize and display this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Embargo Date:
4/17/2006
Resource Identifier:
76786528 ( OCLC )

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Full Text












HYDROGEN ATOM ABSTRACTION REACTIVITY OF A PRIMARY
FLUOROALKYL RADICAL IN WATER















By

JOSEPH AARON CRADLEBAUGH


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


2005

































This work is dedicated to my parents, Charles and Jo, who have always loved and
supported me through the course of my life.















ACKNOWLEDGMENTS

Through the course of my graduate studies here at the University of Florida I have

been blessed with the opportunity to befriend some wonderful people. I can honestly say

that graduate school has been some of the best years of my life, and I would like to

express my appreciation to some special people who have aided in my education.

My respect and gratitude go out to my graduate research advisor, Dr. William R.

Dolbier, Jr., for guiding me in my development as a researcher. I am especially grateful

for his insightful discussions and encouragement during my time at the University of

Florida.

I would also like to thank the members of my supervisory committee for their

advice, and making time in their busy schedules to serve on my committee. They are

Dr. Kenneth Wagener, Dr. Ronald Castellano, Dr. Daniel Talham, and Dr. Anthony

Brennan. I would also like to thank Dr. Ion Ghiviriga for helping me with NMR spectra

interpretation, and instrumental problems.

It has been a pleasure working in the Dolbier research group, and the experience

will never be forgotten. I would like to thank Dr. Li Zhang, Dr. John Marshall Baker, Dr.

Yian Zhai, and Dr. Bob Shelton, for their friendship and helpful discussions. I would

especially like to thank Dr. Tyler Schertz and Dr. Chaya Pooput for their constant words

of encouragement and support. Finally, I would like thank all of the Dolbier group

members, both past and present.









The North Central Soccer Officials Association has been a major source of contact

with people from many different fields and backgrounds. I have enjoyed officiating with

all of the members, and wish them many fun-filled days on the pitch.

Finally, I would like to express my appreciation and love for my parents who have

always supported me.















TABLE OF CONTENTS

page

A C K N O W L E D G M E N T S .................................................................................................. iii

LIST OF TA BLE S .................. .................. .................. .......... .............. .. viii

LIST OF FIGU RE S ..................................... .................. .......... .................... xii

LIST OF SCHEM ES ........................................................... ................... xv

L IST O F E Q U A T IO N S ............................................................ .................................. xvi

A B ST R A C T ... ... ............................................ ........ ......... ...... xvii

CHAPTER

1 GENERAL INTRODUCTION TO RADICAL CHEMISTRY .................................1

1.1 G en eral Intro du action .................................................................. .......... .. .. 1
1.2 Fluorine Substituent E effects ..................................................................... .....2
1.3 Structure of Fluorinated Radicals...................... ....... .................3
1.4 Thermodynamic Properties of Fluorinated Radicals...............................4
1.5 A lkene A addition R actions ............................................ .......................... 6
1.6 Hydrogen Atom Abstractions....................... ...................... 9
1.7 Fluorinated Free Radical Chemistry in Aqueous Solutions.............................13

2 ABSOLUTE RATE CONSTANTS FOR HYDROGEN ATOM ABSTRACTION
REACTIONS BY A PRIMARY FLUOROALKYL RADICAL IN WATER......... 16

2.1 Introduction .................................... ............................... ......... 16
2 .2 R esults....... ............................. ........... .. .... ...... ..... ..... ............. 19
2.2.1 LFP Determination of the Rate Constant for Addition of
*RfSO3 to 2 ........................... .. ... ......... .. ................. 20
2.2.2 LFP Probe Experim ents ...................... ............................ .............. 22
2.2.3 Competition Experiment to Determine kD for THF-d ........................24
2.2.4 Obtaining Relative and Absolute H-Atom Abstraction Rate
C on stants ................................................................ ............... 2 6
2.3 D discussion of the K inetic D ata...................................................... ..................30
2.3.1 Rate Constants for H-Atom Abstractions in Water by Primary
Fluoroalkyl R radicals ................................... ................................... 31


v









2.3.2 Comparison of Rate Constants for H-atom Abstraction by Primary
Fluoroalkyl Radicals in Water and in BTB.......................................32
2 .4 C on clu sion s ................................................................3 5
2 .5 E xperim mental ............................................................ .... .. .... ..... ...... 35
2.5.1 Sodium 5-iodo-3-oxaoctafluoropentanesulfonate (1)............................36
2.5.2 Sodium 4-(P-methyl)vinylbenzoate (2) .............................................. 36
2.5.3 Sodium 5-H-3-oxaoctafluoropentanesulfonate (3H) ..........................38
2.5.4 Kinetic Measurements by Time-Resolved Laser Flash Photolysis .......38
2.5.5 Verification of Probe Addition Rate Constant............... ...............39
2.5.6 Laser Flash Photolysis Probe Experiments........................... .........39
2.5.7 General Procedure for Kinetic Competition Studies ...........................39
2.5.8 Tables of Kinetic Data and Plots ............................... ................. 41

3 RATE CONSTANTS FOR OXYANION ACCELERATED HYDROGEN
ABSTRACTION REACTIONS FROM ALKOXIDES BY A
PERFLUOROALKYL RADICAL IN WATER ...................................................68

3 .1 Introdu action ........................................................................68
3 .2 R results and D iscu ssion ............................................................ .....................7 1
3.2.1 K inetic R esults......................... .. .................... ........ .............. .. ..71
3.2.2 Possible Synthetic A applications .................................... ............... 77
3 .3 C o n clu sio n s ................................................................ 8 1
3 .4 E x p erim mental ........... ... ... ........... ........ ...................... .... ...... ...................82
3.4.1 Typical Procedure for Preparation of Alkoxide Sodium Salts .............82
3.4.2 Preparation of 2-deuteriohexafluoroisopropoxide, sodium salt (8).......83
3.4.3 Typical Procedure for the Preparation of Monobasic Sodium Salts of
H ydrates ..................................... ............ ..................... 83
3.4.4 General Procedure for 19F NMR Kinetic Experiments..........................84
3.4.5 Kinetic Measurements by Time-Resolved Laser Flash Photolysis .......85
3.4.6 Preparation of Com pound 11 ...................................... ............... 85
3.4.7 Tables of Kinetic Data and Plots ........... ............................................88

4 LARGE PRIMARY KINETIC ISOTOPE EFFECTS IN THE ABSTRACTION OF
HYDROGEN FROM ORGANIC COMPOUNDS BY A FLUORINATED
R A D IC A L IN W A TE R ............................................................... .....................102

4.1 Introduction .................................................................. ......... 102
4.2 R esults....... .................. ..... .......... .............................104
4.2.1 Secondary Deuterium Isotope Effects ............................................... 107
4.2.2 Primary Deuterium Isotope Effects ..................................................111
4.3 Discussion. ................................ ............................ ............ 112
4.4 Conclusion ................................. ............................... ......... 116
4 .5 E xperim ental ............................... .... .... .. .... ... ......... .. 116
4.5.1 General Procedure for Competition Kinetic Studies ...........................117
4.5.2 Correction for the Diethyl Ether Impurity in CH3CHDOH..............117
4.5.3 Procedure for Measurement of the Intramolecular Isotope Effects..... 118









4.5.4 Preparation of CH 3CH D OH ............................................ ......... .......119
4.5.5 General Procedure for the Acetone Arrhenius Data........................119
4.5.6 Tables of Kinetic D ata and Plots ........................................................ 121

APPENDIX SELECTED NMR SPECTRA................................. ..................... 133

L IST O F R E F E R E N C E S ...................................................................... ..................... 139

BIOGRAPHICAL SKETCH ............................................................................ 146
















LIST OF TABLES


Table page

1-1. H yperfine splitting constants ......................................... ............... ............... 4

1-2. BD Es for various hydrocarbons ............................................ .......................... 5

1-3. BDEs for fluorinated m ethanes and ethanes..................................... .....................5

1-4. Rho (p) param eters of radical reactions................................... ........................ 6

1-5. Relative rates of radical addition to CF2=CF2/CH2=CH2................. ...............7

1-6. Relative rate of addition of CF3- to alkenes ........ .. ............. ....... ... ............ ..7

1-7. Absolute rate constants for alkene additions at 25 C in Freon 113........................8

1-8. Hydrogen atom abstractions by n-C7F15s and R-CH2' in C6D6 at 30C ...................9

1-9. Absolute rate constants for H-atom abstraction by n-C4F9- at 25 C.......................12

1-10. Absolute rate constants for -RfSO3- addition in water and comparison to Fl 13.....14

2-1. Pseudo 1st order rate constant for probe addition ............................................... 21

2-2. Determination of kH for THF via probe competition ...........................................23

2-3. Rate data for THF/THF-d8 competition towards -RfSO3Na Radical.........................28

2-4. Rate constants for H-atom abstractions ............................................ ...............29

2-5. Rate data for THF/THF-d competition.................................. ....................... 41

2-6. Rate data for CH3OH/THF-ds competition .................................... ............... 42

2-7. Rate data for CH3CH2OH/THF-d8 competition ...................................................43

2-8. Rate data for (CH3)2CHOH/THF-ds competition........................ ............... 44

2-9. Rate data for ethylene glycol/THF-ds competition..............................................45

2-10. Rate data for 2,3-butanediol/THF-d8 competition................... ..................46









2-11. Rate data for methyl glycolate/THF-ds competition ............................................47

2-12. Rate data for CF3CH2OH/THF-ds competition ................... ............................. 48

2-13. Rate data for (CF3)2CHOH/CD30D competition.................... .....................49

2-14. Rate data for CH30CH2CH20CH3/THF-d8 competition............... ...................50

2-15. Rate data for (CH3)2CO/THF-ds competition.....................................51

2-16. Rate data for CH3COOH/THF-ds competition........................ ............... 52

2-17. Rate data for CH3COONa/THF-d8 competition ...............................................53

2-18. Rate data for CH3CH2COOH/THF-d8 competition.............................. ...........54

2-19. Rate data for CH3CH2COONa/THF-d8 competition ............................................55

2-20. Rate data for HSCH2CH2SO3Na/THF-ds competition ......................................56

2-21. Rate data for (HOCH2CH2CH2)3SiH/THF-d8 competition .................................57

2-22. Rate data for Me3N+CH2SiMe2H Br/THF-d8 competition ...................................58

2-23. Rate data for H3PO3/THF-d8 competition ...........................................................59

2-24. Rate constants (kgi) for -RfSO3 + 4-(1-propenyl)benzoate Na 2, in water ..........60

2-25. LFP kinetic probe data yielding kH for THF ................................ .................61

2-26. LFP kinetic probe data yielding kH for isopropanol.............................................66

3-1. Correlation between rate constant and calculated a-C-H BDEs ............................70

3-2. Rate constants for hydrogen abstraction from fluorinated and non-fluorinated
alcohols ............................................................... ..... ...... ........ 71

3-3. Absolute rate constants for alkoxides and corresponding alcohols...........................72

3-4. Absolute rate constants of hydrates and monobasic hydrate anions .........................76

3-5. Summary of attempted chain propagation reactions with 10 ....................................79

3-6. Rate data for sodium hexafluoroisopropoxide/THF-ds competition .........................88

3-7. Rate data for THF/sodium hexafluoroisopropoxide-D competition..........................89

3-8. Rate data for sodium trifluoroethoxide/THF-ds competition ..................................90









3-9. Rate data for sodium hexafluoroisopropoxide/sodium hexafluoroisopropoxide-D
c o m p etitio n .................................................... ................ 9 1

3-10. Rate data for sodium trifluoroethoxide/sodium hexafluoroisopropoxide-D
co m p etitio n .................................................... ................ 9 2

3-11. Rate data for sodium trifluoroisopropoxide/THF-ds competition...........................93

3-12. Rate data for hexafluoroisopropanol/MeOD-d4 competition ................................94

3-13. Rate data for C13CCH(OH)2/THF-d8 competition...................... ................. 95

3-14. Rate data for C13CCH(OH)ONa/THF-d8 competition................ ........... .......96

3-15. Rate data for F3CCH(OH)2/THF-d8 competition.........................................97

3-16. Rate data for F3CCH(OH)ONa/THF-ds competition ...........................................98

3-17. Rate data for H-atom abstraction from sodium trifluoroethoxide by -RfSO3Na in
w after ...................................... .................................................... 9 9

3-18. Rate data for H-atom abstraction from sodium trifluoroisopropoxide by -RfSO3Na
in w after ............................................................... ... .. ..... ......... 101

4-1. Observed kinetic isotope effects for several organic compounds .........................107

4-2. Data used to calculate secondary deuterium isotope effects .................................109

4-3. Corrected prim ary isotope effects............................................................ .......... 112

4-4. Arrhenius data for acetone at 24 C ................................ ................................. 121

4-5. A rrhenius data for acetone at 56 C ................................ ........................ .. ......... 122

4-6. Arrhenius data for acetone at 80 C ................................ ................................. 123

4-7. Rate data for CH30H/CD3OD competition ........... .............. ........................ 124

4-8. Rate data for THF/THF-ds com petition........................................ ............... 125

4-9. Rate data for (CH3)2CHOH/(CD3)2CDOD competition....................................126

4-10. Rate data for CH3CH20H/CD3CD2OD competition ............................................127

4-11. Rate data for CH3CH2OH/CH3CD2OD competition ........................ ..................128

4-12. Rate data for (CH3)2CO/(CD3)2CO competition ................................................129

4-13. Rate data for CH3COOH/CD3COOD competition........................... ...............130









4-14. Rate data for hexafluoroisopropoxide/hexafluoroisopropoxide-d competition.....131

4-15. Rate data for hexadeuteroisopropanol/THF-d8 competition............... ............... 132















LIST OF FIGURES


Figure pge

1-1. Fluorinated radical pyramidalization.................. ....... ......................... 3

1-2. Polar transition state for alkene additions of perfluoroalkyl radicals......................8

1-3. Polar transition states..................................................................10

2-1. Polar transition state for an H-atom abstraction....................................................... 17

2-2. Plot of Pseudo 1st order rates vs. concentration of 2 ..............................................21

2-3. Plot of kexp vs. [TH F] ......... ... ................ ................... ... ...... .......... .... 24

2-4. 19F NMR spectra of hydrogen and deuterium reduced products..............................25

2-5. Plot of [3H]/[3D] vs. [THF]/[THF-d ] ............................. ............................. 28

2-6. Charge separated polar transition state for addition to C=C double bonds ..............33

2-7. Competing H-atom abstraction and P-scission pathways..............................34

2-8. Hydrogen bonding of an alcohol to a water molecule............... ...............35

2-9. Plot of [3H]/[3D] vs. [THF]/[THF-d ] ............................. ............................. 41

2-10. Plot of [3H]/[3D] VS. [CH3 H]/[THF-d ] ...................................... ............... 42

2-11. Plot of [3H]/[3D] vs.[CH3CH20H]/[THF-d ] ................................... ... ..................43

2-12. Plot of [3H]/[3D] VS. [(CH3)2CHOH]/[THF-d]........ ......... ......................44

2-13. Plot of [3H]/[3D] VS. [ethylene glycol]/[THF-ds] .......................................... 45

2-14. Plot of [3H]/[3D] VS. [2,3-butanediol]/[THF-d].................................................46

2-15. Plot of [3H]/[3D] VS. [methyl glycolate]/[THF-ds] ..............................................47

2-16. Plot of [3H]/[3D] VS. [CF3CH2OH]/[THF-d ] .................................................... 48

2-17. Plot of [3H]/[3D] VS. [(CF3)2CHOH]/[CD30D] ................................................... 49









2-18. Plot of [3H]/[3D] VS. [CH30CH2CH20CH3]/[THF-d] ....................................... 50

2-19. Plot of [3H]/[3D] VS. [(CH3)2CO]/[THF-d] .................................. ................ 51

2-20. Plot of [3H]/[3D] VS. [CH3COOH]/[THF-ds]......................................................52

2-21. Plot of [3H]/[3D] VS. [CH3COONa]/[THF-ds]................ .... .................53

2-22. Plot of [3H]/[3D] VS. [CH3CH2COOH]/[THF-d] .....................................................54

2-23. Plot of [3H]/[3D] VS. [CH3CH2COONa]/[THF-d8] .............. ................................55

2-24. Plot of [3H]/[3D] VS. [HSCH2CH2SO3Na]/[THF-ds]..............................................56

2-25. Plot of [3H]/[3D] VS. [(HOCH2CH2CH2)3SiH]/[THF-ds] ....................................57

2-26. Plot of [3H]/[3D] VS. [BrMe3NCH2SiMe2H]/[THF-ds]...................... ..........58

2-27. Plot of [3H]/[3D] VS. [H3PO3]/[THF-d ] .............. .........................................59

3-1. Anionic oxy-Cope rearrangement rate enhancement .............................................68

3-2. Isopropanol reactivities in BTB and water.............. ............. ............... 69

3-3. Photo-sensitized addition of alcohols and cyclic ethers ........................................77

3-4. Plot of [3H]/[3D] VS. [sodium hexafluoroisopropoxide]/[THF-ds] .............................88

3-5. Plot of [3H]/[3D] VS. [THF]/[sodium hexafluoroisopropoxide-D] ...........................89

3-6. Plot of [3H]/[3D] VS. [sodium trifluoroethoxide]/[THF-ds] .....................................90

3-7. Plot of [3H]/[3D] VS. [sodium hexafluoroisopropoxide]/[sodium
hexafluoroisopropoxide-D] .......... .....................................................................91

3-8. Plot of [3H]/[3D] VS. [sodium trifluoroethoxide]/
[sodium hexafluoroisopropoxide-D ] .............. .............. ..................................... 92

3-9. Plot of [3H]/[3D] VS. [sodium trifluoroisopropoxide]/[THF-ds] ..............................93

3-10. Plot of [3H]/[3D] VS. [hexafluoroisopropanol]/[MeOH-d4].............................. 94

3-11. Plot of [3H]/[3D] VS. [C13CCH(OH)2]/[THF-d8] ................ ............. .....................95

3-12. Plot of [3H]/[3D] vs. [C13CCH(OH)ONa]/[THF-d8].................................................96

3-13. Plot of [3H]/[3D] VS. [F3CCH(OH)2]/[THF-d] .................................................. 97

3-14. Plot of [3H]/[3D] vs. [F3CCH(OH)ONa]/[THF-d]] ............... ....... .........98









4-1. Rate constants for H-abstraction from isopropanol in BTB and water ................... 102

4-2. Typical com petition experim ent.......... .................................................. ...... 103

4-3. Competition between acetone and deuterated acetone ............................... 105

4-4. Plot of the kinetic data for acetone ........... ......... .. ........................ ............... 106

4-5. Transition state for D-abstraction from pentadeuteroethanol showing a- and P-
secondary deuterium s ................................................... .................................... 108

4-6. Secondary deuterium isotope effects for a radical forming reaction ...................111

4-7. Temperature profile for acetone, ln(kH/kD) vs. 1/T ............................................115

4-8. Plot of Arrhenius data for acetone at 24 C................. ................................. 121

4-9. Plot of Arrhenius data for acetone at 56 C......... ......................................... 122

4-10. Plot of Arrhenius data for acetone at 80 C....................................................123

4-11. Plot of [3H]/[3D] vs. [CH30H]/[CD30D] ...................... ........... 124

4-12. Plot of [3n]/[3D] vs. [THF]/[THF-ds] ...................................... ............... 125

4-13. Plot of [3H]/[3D] vs. [(CH3)2CHOH]/[(CD3)2CDOD] ................. .. ...................126

4-14. Plot of [3H]/[3D] vs. [CH3CH20H]/[CD3CD20D]........................................... 127

4-15. Plot of [3H]/[3D] vs. [CH3CH20H]/[CHCD20D] ...............................................128

4-16. Plot of [3H]/[3D] vs. [(CH3)2CO]/[(CD3)2CO] ............................. ................. 129

4-17. Plot of [3H]/[3D] vs. [CH3COOH]/[CD3COOD] ...................................... 130

4-18. Plot of [3H]/[3D] vs. [(CF3)2CHO ]/[CF3)2CDO] ........................................... 131

4-19. Plot of [3H]/[3D] vs. [(CD3)2CHOH]/[THF-d]................... ...............132
















LIST OF SCHEMES

Scheme page

1-1. Photo initiated chain reaction ............................ ............................. 11

2-1. Chain reaction involving a hydrogen atom abstraction................ ..................16

2-2. Synthesis of com pound 1................................................. .............................. 18

2-3. Radical generation and addition to sodium 4-(1-propenyl)benzoate.........................20

2-4. Synthesis of sodium 4-(P-methyl)vinylbenzoate (2) ...........................................22

2-5. Formation of hydrogen reduced product ........................................ ...............24

2-6. C om petition experim ent ........................................ ..............................................27

2-7. Possible electron transfer m echanism ................................... ......................... 30

3-1. Competition scheme showing trifluoroethoxide (5) and THF-d ............................72

3-2. C om petition w ith no T H F -d8 ......... ................. .....................................................73

3-3. Preparation of the monobasic sodium salts .................................... ............... 75

3-4. A ttem pted alkene addition of 10 ........................................ ......................... 78

3-5. Dissociation of com pound 11.................................... ..................................... 80

3-6. Synthesis of com pound 11............................................. ................................ 80
















LIST OF EQUATIONS


Equations pge

2-1. G lobal rate constant calculation ........................................... ......................... 21

2-2 K inetic prob e expression ........................................ .............................................22

2-3. Sim plified kinetic probe expression ........................................ ....... ............... 23

2-4. Competition expression for THF/THF-d8 .................................... ........ ...........26

2-5. C om petition m methodology .............................................................. .....................26

3-1. Calculation of kH (HFIPO) without using THF-d ......................................... 74

3-2. Calculation of kH (HFIPO) using a "reverse" competition.......................................74

4-1. Calculation of isotope effects for t-BuMe2SiH and THF ........................................104

4-2. Calculation of the a-secondary deuterium isotope effect for CH3CHDOH ............109

4-3. Calculation of the a-secondary deuterium isotope effect for CHD2OH ..................110















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

HYDROGEN ATOM ABSTRACTION REACTIVITY OF A PRIMARY
FLUOROALKYL RADICAL IN WATER


By

Joseph Aaron Cradlebaugh

December 2005

Chair: William R. Dolbier, Jr.
Major Department: Chemistry

A combination of laser flash photolysis and competitive kinetic methods has been

used to measure the absolute bimolecular rate constants for hydrogen atom abstraction in

water from a variety of organic substrates including alcohols, ethers, carboxylic acids,

fluorinated alkoxides, aldehyde hydrates, and the monobasic sodium salts of aldehyde

hydrates by the perfluoroalkyl radical, -CF2CF20CF2CF2SO3 Na+. Comparison, where

possible, of these rate constants with those previously measured for analogous reactions

in the non-polar organic solvent, 1,3-bis(trifluoromethyl)benzene show that the alcohols

are 2-5 times more reactive in the water solvent and that the ethers react at the same rate

in both solvents. A transition state for hydrogen abstraction that is more reminiscent of

an intimate ion pair than a solvent separated state ion pair is invoked to explain these

modest solvent effects.

The bimolecular rate constants observed for the 0-fluorinated alkoxides were in the

105 M-1 s-1 range, such rates representing enhancements over their respective alcohols of









between 100 and almost 1000-fold, depending on the reactivity of the alkoxide.

Likewise, the monobasic sodium salts of chloral and floral hydrate exhibit similar rate

enhancements, relative to their respective hydrates. In addition, the largest bimolecular

rate constant ever observed for hydrogen atom abstraction by this radical is determined

for the monobasic sodium salt of fluoral hydrate.

Kinetic isotope effects have also been determined for the abstraction of hydrogen

from a series of organic substrates. Both primary and secondary deuterium isotope

effects were measured, with the primary isotope effects ranging in value from 4.5 for

isopropanol to 21.1 for acetic acid. The values for the a- and P-secondary deuterium

isotope effects were 1.06 and 1.035 respectively. It was concluded that tunneling

contributes significantly to the production of the observed, large primary kinetic isotope

effects in these C-H abstraction reactions.


xviii














CHAPTER 1
GENERAL INTRODUCTION TO RADICAL CHEMISTRY

1.1 General Introduction

Organic synthesis involving free radicals as reactive intermediates has advanced

immensely over the past century. 1-3 The beginning of radical chemistry can be traced

back to work presented by Gomberg in 1900 on "Triphenylmethyl: An Instance of

Trivalent Carbon." 4 However, a true understanding of the mechanistic implications of

radical chemistry had to wait until the 1930s when a review by Walters and Hey

demonstrated that radical mechanisms were viable for a number of known reactions.

Despite the early advances in radical chemistry, carbon-based free radical chemistry was

not viewed as feasible for organic synthesis, and thus, lay largely dormant for many

years. This view is perhaps best exemplified in Walling's 1985 perspective, "radical

chemistry remained essentially mysterious" to synthetic chemists. 6

As the synthetic community toiled with an understanding of carbon-based free

radical chemistry, important progress had already been made in the area of polymer

chemistry. Flory established the practicability of utilizing carbon-based free radical chain

processes of olefins to yield commercially valuable polymers. 7'8 Free radical

polymerization is of paramount importance today both in industrial and laboratory

preparations of remarkable materials, such as TEFLON. 9, 10 Free radical chemistry

made headway in synthesis in the mid 1980s. Hart successfully showed in the synthesis

of pyrrolizidines that radical chemistry could provide easy access to families of natural

products. 11 Stork demonstrated that radical reactions were capable of a high degree of









regio- and stereoselectivity. 12 This progress in synthetic radical chemistry has led to an

explosion in the use of free radical intermediates in chemistry today. 13-16

Even with the plethora of advances in the field of radical chemistry, very few

results have been reported studying fluorinated radicals in aqueous media. The

fluoropolymer industry is unique in this aspect with the main thrust of its production

methods utilizing fluoroalkyl radicals in aqueous solution. However, no kinetic data on

hydrogen atom abstraction by fluoroalkyl radicals from organic donors have ever been

published. The manufacture of industrial fluoropolymers typically requires the use of H-

transfer agents to control molecular weight and molecular weight distributions under

aqueous dispersion, suspension, or emulsion polymerization conditions. 17-19Common

chain transfer agents include chloroform, hydrocarbons, alcohols, and ethers. 20, 21 But the

recipes for their use are entirely empirical and there have been no systematic, quantitative

kinetic data on their reactivity toward model propagating fluorinated radicals in aqueous

media to guide their use, or the design of improved chain transfer agents.

1.2 Fluorine Substituent Effects

Most of the influence fluorine, as a substituent, exhibits on radical structure and

reactivity is a direct result of the extreme electronic nature of fluorine. 22 There are

generally two types of substituent effects: steric effects and polar (electronic) effects.

Polar effects can be divided further into a inductive and 7n conjugative (resonance)

effects. Due to fluorine's small size, steric effects in the transition states of fluorinated

free radical reactions do not play an integral role in their reactivity. As a consequence of

fluorine being the most electronegative atom, fluorine is a strong a inductive electron

withdrawing group in all cases. However, bound fluorine atoms have 3 lone pairs of

electrons in sp3 orbitals which may act as a very good n electron donor to other n









systems. In relation to fluorinated free radicals, fluorine's lone pair participates in orbital

overlap with the semi-occupied molecular orbital (SOMO) of the radical center. The key

to understanding substituent effects is to separate the 7n resonance effects from the a

inductive effects, which is impossible for a substituent such as fluorine. The interplay of

these contrasting polar effects makes for a complicated electronic picture.

1.3 Structure of Fluorinated Radicals

Unlike the complex situation surrounding electronic effects, fluorine substitution

has definite ramifications on the structure of radicals. For instance, the methyl radical

has been shown by ESR spectroscopy to exist in a planar conformation. 23 Conversely,

the outcome of fluorine substitution on the radical's conformation is a tendency to

become pyramidal (Figure 1-1). 23-25



H H i F

F F
Planar Methyl Radical Tetrahedral Trifluoromethyl Radical

Figure 1-1. Fluorinated radical pyramidalization

As mentioned before, ESR spectroscopy is the best method for determining the

geometry of a radical. Nonplanarity brings about more s character in the SOMO which

contains an unpaired electron. In terms of ESR spectroscopy, the increased s character is

manifested by a greater ESR a13C hyperfine (hfs) splitting constant. The methyl radical

has an a13C value of 38 G, which indicates a planar geometry. Upon fluorine substitution

of the radical, it is not surprising that the a13C values increase greatly, with the

trifluoromethyl radical having a value of 272 G, which indicates an sp3 hybridization.

(Table 1-1). 23

















The electronegativity of fluorine is the primary cause of the observed structural

changes upon fluorine substitution. Bent's rule states, "Atomic p character concentrates

in orbitals directed toward electronegative substituents," which permits more

electronegative atoms a greater share of bonding electrons. 26 In addition, the unpaired

electron in the SOMO would be thermodynamically more stable because the SOMO will

take on more s character as the number of fluorines is increased. Conjugative effects may

also contribute to the observed pyramidalization, but work has been done showing that

fluorine's predominant influence is due to its strong a inductive withdrawing effect. 27

1.4 Thermodynamic Properties of Fluorinated Radicals

The ability of fluorine substituents to stabilize alkyl radicals centers on the same

interaction between inductive and resonance effects which determines their structure.

Substituents which are electronegative and bear lone pairs of electrons are expected to

destabilize the radical via their a withdrawing ability, and stabilize by their 7t donation to

the extent that the single electron is delocalized. Bond dissociation energies (BDEs) have

historically been used as a measure of radical stability. C-H BDEs for various

hydrocarbon radicals are given in Table 1-2 and show that there is a direct correlation

between radical stability and increased substitution. 28, 29 The same type of stabilization is

observed for carbocations (3 > 2 > 1 > CH3) and can be attributed to hyperconjugative

effects. The C-H BDEs of fluorinated methanes and ethanes are given in Table 1-3, and

show quite different stabilization effects than their hydrocarbon analogues.

















From the data it can be determined that one or two a-fluorines provides slight

stabilization, albeit destabilization is observed for the trifluoromethyl case. 28,29

Table 1-3. BDEs for fluorinated methanes and ethanes
BDE, kcal/mol

CH3-H 104.8

CH2F-H 101.2

CHF2-H 103.2

CF3-H 106.7

CH3CH2-H 101.1

CF3CH2-H 106.7

CH3CF2-H 99.5

CF3CF2-H 102.7



Although the experimental data for the ethane series are limited, it does appear that

p-fluorine substitution results in radical destabilization. It has been suggested by

computational efforts that the inductive effect of a single fluorine atom adequately

destabilizes an ethyl radical. 30









1.5 Alkene Addition Reactions

To obtain an understanding of fluoroalkyl radical reactivity, the philicity of such

radicals must be ascertained. Free radicals are classified as either nucleophilic or

electrophilic depending on their reactivity characteristics in situations of differing

electronic demand. Various Hammett studies have been performed to determine the

electrophilicity or nucleophilicity of radicals, which are reflected by the rho (p)

parameters. Table 1-4 lists rho (p) parameters for additions to substituted styrenes and

the H-atom abstractions of radicals from substituted toluenes.

Table 1-4. Rho (p) parameters of radical reactions
Radical a H-Atom Abstraction fromToluene Addition to Styrene

P P P P

CH3 -0.1 -0.12

(CH3)C 0.49 1.1

c-C6H 1 -- 0.68

n-C6H13 0.45

n-C11H23 0.45

(CH3)3CO -0.32 -0.36 -0.27 -0.31

CC13 -1.46 -1.46 -0.42 -0.43

n-CsF17 -0.53

a. references 31-41

From the p parameters it is obvious that hydrocarbon radicals have nucleophilic character

and the halogenated and oxygen-centered radicals have electrophilic character. 31-33,42

The importance of philicity is also observed in the relative rate of addition of increasingly

electrophilic radicals to ethylene and tetrafluoroethylene. Table 1-5 illustrates that









increasing the electrophilicity of radicals leads to slower addition rates to the electron

poor alkene. 4345

Table 1-5. Relative rates of radical addition to CF2=CF2/CH2=CH2
Radical kcF2 CF2 / kCH2=CH2

CH3 9.5

CH2F 3.4

CHF2" 1.1

CF3 0.1



Szwarc also demonstrated how the electrophilicity of CF3- affects overall addition

rates to various alkenes. As shown in Table 1-6, the rate of radical addition increases for

the more electron rich alkenes. 46

Table 1-6. Relative rate of addition of CF3- to alkenes
Alkene krei

3.7


1.4

1

F F 0.15




Having established the fact that electrophilic fluorinated radicals add to electron

rich olefins at an accelerated rate over electron poor olefins, it becomes necessary to

compare the rates of addition of fluorinated radicals and their hydrocarbon analogues.

One would predict the reactivity of fluoroalkyl radicals to differ significantly from their

hydrocarbon counterparts. The latter are planar, electron rich n-radicals, whereas









fluoroalkyl radicals have been shown to be pyramidal, electron poor C-radicals. Absolute

rate data for the addition of perfluoroalkyl radicals to various alkenes in solution have

been obtained by laser flash photolysis (LFP). 47,48 Table 1-7 shows the absolute rate

constants, kadd, for perfluoroalkyl radical additions to several alkenes in Freon 113.

Table 1-7. Absolute rate constants for alkene additions at 25 C in Freon 113
Alkenes kadd(106M1 s-1)

n-C3F7 n-C7F15 C2F5 CF3 RCH2

a-methylstyrene 78 89 94 87a 0.059b

p-methylstyrene 3.8 3.7 7 17 -

styrene 43 46 79 53 a 0.12 d

pentafluorostyrene 13 23 26 a 0.31 a

1-hexene 6.2 7.9 16 2x 10-4e

1,4-dimethylenecyclohexane 41 1 x 10-4 e

a. Reference 49; b. Reference 50; c. Reference 51; d. Reference 52; e. Reference 53

It is apparent that fluoroalkyl radicals exhibit much more reactivity than their

hydrocarbon analogues, with n-C3F7- adding 30,000 times faster to 1-hexene and 1,300

times faster to a-methylstyrene than the alkyl radical.

The high electrophilicities of perfluoroalkyl radicals appears to be the dominant

factor which gives rise to their great reactivities in relation to their alkyl counterparts. 48

5-
CF3CF2CF2

5+
HI.I II,, -n H

H R
Figure 1-2. Polar transition state for alkene additions of perfluoroalkyl radicals









Polarization of the type shown in Figure 1-2 will stabilize the charge separated transition

state in which only a small amount of radical character is conveyed to the alkene.

1.6 Hydrogen Atom Abstractions

The rates of hydrogen atom abstractions by radicals are governed by the same

factors which influence the rates of alkene additions. 54 Polar effects and thermodynamic

considerations are extremely important in understanding rates of hydrogen abstraction.

As might be expected, the BDE of the compound in which the hydrogen atom is being

abstracted plays an apparent role. Table 1-8 gives absolute rate constants for the

hydrogen atom abstraction reactions for both an n-alkyl and perfluoroalkyl radical (Rf)

from electropositive donor atoms with benzenethiol electronegativee) being the

exception, and correlates the BDE of the donors to the observed absolute rate

constants.55-57 All rate constants were determined via a combination of LFP and

competition techniques. The BDEs simply reflect that the lower the bond dissociation

energy for the electropositive donors, the faster the hydrogen atom abstraction for the two

radicals since in all cases the new bond being formed is C-H.

Table 1-8. Hydrogen atom abstractions by n-C7F15- and R-CH2' in C6D6 at 30C
kH / 106 M1 s-1

Radical Et3SiH (TMS)2SiMeH (TMS)3SiH n-Bu3SnH PhSH

n-C7F15- 0.75 16.3 51 203 0.28

R-CH2- 0.0007 0.037 0.46 2.7 150

BDE, kcal/mol 90.1 a 85.3 a 79.0 a 73.6 b

a. Reference 58; b. Reference 59

In comparing the reactivity of the two primary radicals, n-C7F15- abstracts hydrogen from

n-Bu3Sn-H -75 times greater than the n-alkyl radical in deuterated benzene at 30C.









(TMS)3SiH showed an increased reactivity for n-CyF15- over R-CH2' of-111 times, and

(TMS)2SiMeH was -441 times greater for the perfluoroalkyl radical. The Et3SiH proved

to be the poorest hydrogen donor of the electropositive donors, but showed the largest

difference in reactivity of -1000 times.

For all the electropositive hydrogen donors, clearly the rates of hydrogen atom

abstractions are significantly greater with the fluoroalkyl radical. McMillen and Golden

have calculated that the BDE of R-H is approximately 9 kcal/mol greater than R-H. 60

Therefore, the increased exothermicity of hydrogen atom abstractions to perfluoroalkyl

radicals is likely the main cause of their greater reactivity over the alkyl counterparts.

Another possible factor controlling the reactivity of hydrogen atom abstractions is

evident in close examination of the rate data associated with benzenethiol. In fact PhSH

is the only instance given in which the rate of hydrogen atom abstraction is actually

larger for the alkyl radical. The reason that the alkyl radical abstracts hydrogen atoms

536 times faster than the perfluoroalkyl radical is apparent when polar factors in the

transition states are examined. Figure 1-3 shows that for electropositive atoms such as

silanes and stannanes, a favorable polarity is achieved in the transition state when they

are reacted with electrophilic perfluoroalkyl (Rf) radicals.

: t
[- 6+ [8+ 8-
Rf -- H----MR3 R'--------H----SPh

Perfluoroalkyl radical preferred Alkyl radical preferred

Figure 1-3. Polar transition states

However, benzenethiol is an electronegative hydrogen atom donor and prefers to react

with nucleophilic alkyl radicals.









Until this point all hydrogen atom abstractions mentioned have involved the use of

metal hydride donors, or benzenethiol. Due to their extreme electrophilicity,

perfluoroalkyl radicals are able to rapidly abstract hydrogen atoms from some organic

compounds, whereas alkyl radicals can not sufficiently abstract hydrogen atoms to

continue chain processes for synthetically useful reactions. Paleta has shown that clean

chain processes occur between fluorinated alkenes and alcohols upon irradiation

(Scheme 1-1). 61,62

H

hv
(CH3)2CHOH + CF2=CFOC2F5 (CH3)2C-CF2CFOC2F5

OH
Maj or product

Scheme 1-1. Photo initiated chain reaction

The absolute rate constants for hydrogen atom abstraction for highly electropositive

atoms were in the 106 108 M-1 s1 range. Due to carbon not being as electropositive and

the fact that the BDE of C-H bonds are greater than that of metal hydrides, hydrogen

atom abstraction from organic compounds is much slower. Prior to the work presented in

this dissertation, the only absolute rate constants for hydrogen atom abstractions were for

perfluoroalkyl radicals in 1,3-bis(trifluoromethyl)benzene (1,3-BTB). The absolute rate

constants were obtained through a bimolecular competition using t-BuSiMe2D as a

deuterium donor, and a wide range of organic compounds as hydrogen donors. 63

t-BuSiMe2D has a known rate of deuterium abstraction by perfluoroalkyl radicals in 1,3-

BTB (kD = 1.49 x 105 M-1 s-1). 64 Absolute rate constants for hydrogen atom abstractions

by n-C4F9- in 1,3-BTB at 25 C are given in Table 1-9. 63,64 1,2-dichloroethane had the









slowest rate, whereas tetrahydrothiophen had the fastest rate, which represented a 1000

fold difference in reactivity.

Table 1-9. Absolute rate constants for H-atom abstraction by n-C4F9 at 25 C
Hydrogen Donor kH / 102 M-1 s- Hydrogen Donor kH / 102 M-' s-

CICH2CH2Cl 0.6 1,3,5-trioxane 9.7

C6H13C1 21 1,4-dioxane 31

n-heptane 76 THP 70

cyclohexane 93 CH30CH20CH3 19

cyclopentane 104 (CH30CH2)2 67

CH30H 9.2 diethyl ether 220

(CH3)2CHOH 163 1,3-dioxolane 140

(CH3CHOH)2 50 THF 310

CH30CH3 28 tetrahydrothiophene 355



The results listed in Table 1-9 illustrate the importance of steric, thermodynamic, and

especially polar effects. For instance, even though an a-chlorine is thermodynamically

stabilizing, the observed C-H abstraction rate is severely hampered. 1-chlorohexane has

been shown to have an overall per hydrogen reactivity which is considerably less than

that of n-heptane. 64 Data have been presented that indicates that the per hydrogen rate

constant for C-H abstraction from a methyl group of n-heptane is 2.4 times larger than

that of the CH2C1 carbon of 1-chlorohexane. 64 Moreover, none of the methyl groups of

1-chlorohexane are as reactive as n-heptane's. Clearly, the electron-withdrawing chlorine

atom is destabilizing the normal transition state polarity associated with hydrogen atom

abstraction.









1.7 Fluorinated Free Radical Chemistry in Aqueous Solutions

The use of water as a solvent for organic reactions has been a subject of much

review since the 1990's. 65-67 SN1 solvolysis reactions have been shown to be accelerated

in aqueous solutions due to strong interactions between carbenium ions and water in the

transitions state. Also, the use of water as a solvent is believed to be much better than

organic solvents with respect to the environment.

Literature pertaining to radical chemistry conducted in water has been practically

non-existent thus far. In the early 1990s, water soluble tin reagents were synthesized for

use in aqueous phase radical reactions. 68, 69 Most of the literature involving free radicals

in water were viewed from a "green chemistry" point of view, until 2000 when the

Fujimoto group reported that triethylborane induced atom transfer radical cyclization was

found to proceed much better in water than other organic solvents. 70 As previously

mentioned, polymer chemistry has utilized aqueous phase radical chemistry for many

years. 71,72 Many different types of high weight polymers can be synthesized by aqueous

phase radical chemistry. The temperature can easily be controlled for these reactions due

to the ability of water to transfer heat readily. In addition, water has distinct advantages

of being neither flammable nor toxic.

The Dolbier group published kinetic data for addition to various substituted

styrenes by a primary fluorinated radical in water. 73 A water soluble fluoroalkyl radical

(NaO3SCF2CF20CF2CF2' or -RfSO3 ) was generated by LFP and was observed, via UV

spectroscopy, adding to water soluble styrenes. As was the case for alkene addition

reactions in organic solvents, thermodynamic and polar effects were observed to be

important factors in understanding the reactivity. It was also determined upon

comparison of relative rate constants for the same series of styrenes in F 13, that steric









and thermodynamic factors were independent of the solvent. In addition, rate constants

for the series in water were 5-9 times faster than was observed for the same series in

F113 (Table 1-10). 73

Table 1-10. Absolute rate constants for -RfSO3- addition in water and comparison to
F113
Styrene kadd / 107 M-1 s-1 k(H20) / k(F 113)


Ph-(p-CO2Na) 23.2 5.4

55.3 7.1
Ph-(p-CO2Na)

'Ph-(p-CO2Na) 3.31 8.7

NaO2C-' Ph 1.88 5.0

Ph-(p-CH2CO2Na) 20.2 4.7



The reasoning given for the rate enhancements in water derived from the more effective

stabilization of the polar transition state by the polar solvent, water, over the nonpolar

organic solvent, F113 (see figure 1-2). Will the increased polarity of water accelerate

hydrogen atom abstractions also?

Due to the high value of fluoropolymers, the fluoropolymer industry has by far

made the most progress in fluorinated free radical chemistry in water. Perfluoroalkenes

can only be converted to high molecular weight polymers by free radical conditions. The

polymerization of tetrafluoroethylene (TFE) is carried out in aqueous media by a couple

of different methods to yield polytetrafluoroethylene (PTFE). Most fluoropolymers are

made by aqueous dispersion, suspension, or emulsion techniques, and even though these

techniques have stood the test of time, there are still problems to be solved in the field.









Perhaps the most evident problem in fluoropolymer production is the early termination of

chain processes due to hydrogen atom abstraction by the propagating fluoro-radical.

Early termination results in low molecular weights for the polymer. The manufacture of

industrial fluoropolymers typically requires the use of H-transfer agents to control

molecular weight and molecular weight distributions under aqueous dispersion,

suspension, or emulsion polymerization conditions. 17, 18, 19 Common chain transfer

agents include chloroform, hydrocarbons, alcohols, and ethers. 20,21 But the recipes for

their use are entirely empirical and there have been no systematic, quantitative kinetic

data on their reactivity toward model propagating fluorinated radicals in aqueous media

to guide their use, or the design of improved chain transfer agents.

Therefore, an understanding of structure-reactivity relationships and the influence

of reaction medium on the kinetics of C-H abstraction by perfluoroalkyl radicals has both

scientific and practical relevance. With these factors in mind, the hydrogen atom

abstraction reactivity of a primary fluoroalkyl radical in water will be studied to provide

insight on whether solvent polarity and structural changes to various hydrogen atom

donors can indeed effect the rates of hydrogen atom abstractions. No kinetic data on

hydrogen atom abstraction by fluoroalkyl radicals in water from organic donors have ever

been published. The work presented here provides the first set of such data.













CHAPTER 2
ABSOLUTE RATE CONSTANTS FOR HYDROGEN ATOM ABSTRACTION
REACTIONS BY A PRIMARY FLUOROALKYL RADICAL IN WATER

2.1 Introduction

Perfluoroalkyl radicals exhibit unusual reactivity characteristics which derive

largely from their great electrophilicity but also, in part, from their pyramidal geometry at

the radical center and the thermodynamics of their reactions. 74 75 Thus, rate constants for

hydrogen atom abstraction by perfluoroalkyl radicals from relatively electropositive

atoms such as Sn, Si, and even from carbon are much larger than those of the analogous

alkyl radicals. For example, the rate constants for hydrogen abstraction from n-Bu3SnH

and Et3SiH by a primary perfluoroalkyl radical (n-Rf) are 85 and 1000 times larger,

respectively, than by n-R. 557

Although the C-H bonds of simple functionalized or non-functionalized aliphatic

organic compounds are effectively inert towards abstraction by alkyl radicals,

perfluoroalkyl radicals are sufficiently reactive that they can efficiently propagate

synthetically useful free radical chain reactions, such as the one given in Scheme 2-1. 61

0 0


\ O__ (94%)
Scheme 2-1 Chain reaction involving a hydrogen atom abstraction2CHFCF
+ F2C CFCF3 (940)



Scheme 2-1. Chain reaction involving a hydrogen atom abstraction









Similarly, and as discussed by Shtarev et al.,63 rate constants for the reactions of the

n-octyl radical with THF and diethyl ether at 22 C (4.9 x 102 and 1.2 x 102 M-1 s1,

respectively) 76, 77 are considerably lower than those for the n-C4F9-, 3.1 x 104 and

2.2 x 104 M-1 s-1, respectively, in 1,3-bis(trifluoromethyl)benzene (BTB). These and

many other rate constants were obtained via competition experiments in which the

relative rates of H-atom abstraction from the substrates were determined versus

deuterium abstraction from t-BuSiMe2D (for which kD = 1.49 x 105 M-1 s-1). 63 Their

work indicated that the rate constants for H-atom abstraction by the n-C4F9- radical

depended on at least three factors: (i) the C-H bond dissociation enthalpy (BDE)

(ii) steric effects and (iii) transition state polar effects. With regard to the last factor, it is

worth noting that chloroalkanes are less reactive towards n-C4F9- than alkanes despite the

fact that a chlorine atom lowers the C-H BDE at the carbon bearing the chlorine relative

to the C-H BDE of the corresponding alkane. The electron-withdrawing chlorine atom

clearly destabilizes the "normal" polarized transition state for C-H abstraction by the

electronegative n-C4F9- radical (Figure 2-1).




----H---- CF2CF2CF3




Figure 2-1. Polar transition state for an H-atom abstraction

Due to high electrophilicities and the acknowledged importance of transition state

polar effects on the reactivities of perfluoro-n-alkyl radicals in both hydrogen

abstractions and alkene additions,74'75 the rates of such reactions might be expected to be

strongly influenced by solvent polarity. 78 The only mention in literature pertaining to this









matter appeared in a footnote in an earlier publication reporting that CF3- and n-C3F7- add

to styrene -3 times and to pentafluorostyrene -1.5 times more rapidly in acetonitrile than

in 1,1,2-trichloro- 1,2,2-trifluoroethane (F 113). 49 A broad investigation of absolute rate

constants for alkene addition reactions of fluorinated alkyl radicals in water has recently

been published. 73 Since the rate constants for alkene additions and hydrogen abstractions

in non-polar solvents (F 113, C6D6, and BTB) are known,63'75 it should be possible to

assess the significance of solvent effects on these reactions. To study perfluoroalkyl

radicals in water, a water soluble radical source must be acquired. The perfluoroalkyl

iodide radical precursors used in non-polar solvents are not soluble in water. Sodium

5-iodo-3-oxaoctafluoropentanesulfonate 1 (ICF2CF20CF2CF2SO3Na) proved to be a

good water soluble model for the perfluoroalkyl iodides. Known compound 1 can be

easily prepared via hydrolysis of ICF2CF20CF2CF2SO2F (Scheme 2-2). 73

H20, 90C
ICF2CF2OCF2CF2SO2F + 2NaOH >- ICF2CF2OCF2CF2SO3Na
12 hrs, 90%
1

Scheme 2-2. Synthesis of compound 1

Elemental analysis indicated that the isolated product is ICF2CF20CF2CF2SO3Na-H20.

Compound 1 will be abbreviated as IRfSO3 from this point forward. IRfSO3 shows a

broad absorption (max = 262 nm) in the UV/Vis. spectrum, which allows for

photoinitiation to yield the reactive radical intermediate. In the initial study, absolute rate

constants for the addition of the -RfSO3 to a series of water soluble alkenes bearing

carboxylate ion functionality in aqueous solution were measured via laser flash

photolysis (LFP). 73 As was the case for the related studies in F113 it was concluded that

thermodynamic, polar, and steric effects probably all played some role in the dynamics of









these additions. In particular, rate constants in water, although nearing the diffusion

limit, were all larger than those reported earlier for their structural counterparts in F 113,

with rate enhancements of 3-9 fold. 48 It was concluded that these enhancements in water

vs. F113 most probably arose from a more effective stabilization of the polar transition

state for addition in the more polar solvent.

Important for the work presented here in relation to hydrogen atom abstractions,

one of the alkenes examined in the earlier LFP study (sodium 4-(1-propenyl)benzoate)

was used as a kinetic probe in further LFP experiments to obtain absolute rate constants

for H-atom abstraction by the fluoroalkyl radical (RfSO3 ) from THF and isopropanol in

water.

2.2 Results

To obtain absolute rate constants for hydrogen atom abstraction from organic

substrates by the -RfSO3 radical in water, it is necessary to determine at least one such

rate constant directly. However, there is no known method to directly measure the rates

of these fast, highly exothermic H-atom abstractions. Consequently, an indirect

competition method was necessary to determine absolute rate constants in water for H-

atom abstraction by -RfSO3 from a diverse range of substrates. The course of action was

to use an LFP "probe" experiment in conjunction with relative rate constants obtained

from competition experiments to derive absolute rate constants for H-atom abstraction.

The following scheme was devised:

A. Determine the global rate constant of the primary fluoroalkyl radical, RfSO3 with

sodium 4-(P-methyl)vinylbenzoate (CH3CH=CHC6H4CO2Na, 2) in water by LFP.

B. Use 2 as a kinetic "probe" to determine the rate constants for H-abstraction by

-RfSO3 from THF and isopropanol.









C. Determine the rate constant for deuterium abstraction from THF-ds by -RfSO3 via a

direct competition between H-atom abstraction from THF and deuterium atom

abstraction from THF-ds.

D. Determine the relative rate constants for H-atom abstraction from a series of organic

substrates vs. D-atom abstraction from THF-ds via competition experiments and then

convert these to absolute rate constants.

2.2.1 LFP Determination of the Rate Constant for Addition of -RSO3 to 2

-RfSO3 radical is generated instantaneously by 308 nm LFP of the parent iodide in

water at ambient temperature (Scheme 2-3).

hv
Na 03SCF2CF2OCF2CF2J H20 Na 03SCF2CF2OCF2CF2
H20
(NaO3SRfl)
kexp
kexp NaO2C r
2



RfSO3Na

NaO2C
Xmax = 320 nm
Benzyl radical

Scheme 2-3. Radical generation and addition to sodium 4-(1-propenyl)benzoate

In the presence of 2, the radical adds to the double bond leading to a benzyl radical

transient which can be detected at 320 nm in the UV/Visible spectrum. The grow in of

the benzyl radical follows pseudo-first-order-kinetics and the global rate constant can be

calculated from the experimental growth curves measured over a range of concentrations

of 2 (Equation 2-1).












kexp (320 nm) = ko + kgl[2]


Equation 2-1. Global rate constant calculation


As discussed previously,48 the global reactions of RfSO3 with an alkene such as 2 are


comprised almost entirely of addition, with less than 5% being due to H-abstraction, i.e.,


kgi = kadd. An example of the kinetic data obtained for these additions is shown in Table


2-1, and Figure 2-2.


Table 2-1. Pseudo 1st order rate constant for probe addition
2/M kexp / -1


5.89 x 103 2.38 x 105


4.16 x 103 1.81 x 105


3.21 x 10-3 1.32 x 105


2.21 x 10-3 1.08 x 105


1.68 x 10-3 7.27 x 104


k(exp) vs 2


300000


250000


200000


150000


100000


50000


0
0 0001


0002 0003 0004


0005


0006 0007


[2]


Figure 2-2. Plot of Pseudo 1st order rates vs. concentration of 2


y= 3841E+07x+ 1 459E+04
R2= 9 880E-01









The slope of the plot of kexp values vs. [2] yields the second order rate constant,

kadd = 3.9 x 107 M- s', as an average for two trials. Known compound 2 was prepared in

three steps from p-bromobenzaldehyde (Scheme 2-4). 80

0

CH=CHCH3

CH3CH2PPh3Br, n-BuLi
Br THF, 92%
Br

1. t-BuLi, THF, -78 C
2. C02, HW, 95%


CH=CHCH3 CH=CHCH3

NaOH, MeOH
72%
NaOOC HOOC
2

Scheme 2-4. Synthesis of sodium 4-(P-methyl)vinylbenzoate (2)

The first step involves a Wittig reaction to give p-bromo-P-methylstyrene, followed by a

lithium halogen exchange with t-BuLi and carbonation with CO2. The Sodium salt is

obtained upon treatment with NaOH until neutral pH is obtained.

2.2.2 LFP Probe Experiments

Although the alkyl radicals derived by H-atom abstraction from THF and

isopropanol have insufficient extinction coefficients to be monitored by UV/Vis.

spectroscopy, the rate constants for the reactions of these H-donors with -RfSO3 can be

obtained by using 2 as a kinetic probe (equation 2-2). 79

kexp (320 nm) = ko + kgi[2] + kH[H-Donor]

Equation 2-2. Kinetic probe expression









The experimental pseudo-first-order rate constant is now the sum of the rate

constants for addition to 2 and H-atom abstraction from the H-donor. At constant

[2] Equation 2-2 can be simplified and Equation 2-3 is obtained.

kexp (320 nm) = ko + kH[H-Donor]

Equation 2-3. Simplified kinetic probe expression

Plots of kexp vs. [H-Donor] yield straight line fits with R2 greater than 0.96 in all cases.

The second order rate constants, kH, for H-atom abstraction are readily obtained from the

slopes of these lines. For THF and isopropanol, kH = 3.3 x 104 and 4.0 x 104 M-1 s-,

respectively, for an average of three or more experiments each. An example of the

kinetic data obtained for the kinetic probe experiments is given in Table 2-2 and Figure

2-3 for THF. Both THF and isopropanol were chosen for these kinetic probe experiments

because they have similar rate constants to that of probe 2.

Table 2-2. Determination of kH for THF via probe competition
[THF]/M kexp / s-1 [2]/M

0.00 7.04 x 104 1.70 x 10-3

0.129 7.35 x 104 1.70 x 10-3

0.194 7.96 x 104 1.70 x 10-3

0.290 7.99 x 104 1.70 x 10-3

0.436 8.39 x 104 1.70 x 10-3

0.653 8.96 x 104 1.70 x 10-3

0.980 1.04 x 105 1.70 x 10-3

1.470 1.18 x 105 1.70x 10-3











Rate of hydogen abstraction from THF


120000


100000


80000


60000


40000


20000


0


0 02 04 06 08
[THF]


12 14 16


Figure 2-3. Plot of kexp VS. [THF]

2.2.3 Competition Experiment to Determine kD for THF-ds

The reaction of the perfluoroiodide with THF using UV initiation proceeds via a


clean, rapid free radical chain process to give reduced product, 3H, in essentially


quantitative yield (Scheme 2-5).


hv, RT
Na03SCF2CF20CFCF2I RT Na03SCF2CF2OCF2CF2H
THF, HO
nTI, H20 3H (NaO3SRfH)
quant.

Scheme 2-5. Formation of hydrogen reduced product

Compound 3H has been characterized and is included in the experimental section. The

ratio of the rate constant for H-atom abstraction from THF to D-atom abstraction from


THF-ds, was determined by using various mixtures of THF and THF-ds and measuring


[Na03SRfH]/[ NaO3SRfD] ratios. As reported earlier, the 19F NMR signals for


y =32438x + 70527
R2 = 0 9906










HCF2CF20CF2CF2SO3 (3H) and DCF2CF20CF2CF2SO3 (3D) are well separated and a

simple integration of the signals provides the relative concentrations of these two

products (Figure 2-4). 63


37.5 -138.0


-138.5 -139.0 -13


Figure 2-4. 19F NMR spectra of hydrogen and deuterium reduced products

The hydrogen reduced product appears as a doublet of triplets at -138.3 ppm, and the

deuterium reduced product shows up as a multiple at -139.0 ppm in the 19F NMR. A

plot of the [3H]/[3D] ratios vs. the [THF]/[THF-ds] ratios gives a straight line

(Equation 2-4), the slope of which is the kinetic isotope effect, kH/kD = 7.9 + 0.4 and


I









since the value of kH is known kD can be calculated. Hence, kD = 3.3 x 104 / 7.9 =

4.2 x 103 M- s"\


[3H] kH [THF]
[3D] kD[THF-ds]

Equation 2-4. Competition expression for THF/THF-ds

With the rate constant for kD(THFd8) in hand, it now becomes possible to calculate the

absolute rate constants for a number of organic H-atom donors.

2.2.4 Obtaining Relative and Absolute H-Atom Abstraction Rate Constants

Competition experiments using THF-ds and an H-donor permitted fast, clean, high

yield reactions with virtually all of the organic substrates studied. Many other D-donors

were investigated for use in competition experiments, but THF-ds appears to be superior

for our competition experiments. As briefly mentioned in the previous section, by

varying the starting concentration of the H-donor a plot of the product ratio (from 19F

NMR) versus the ratio of reactant concentrations yields a linear correlation. The

competition methodology expression is given for all cases in Equation 2-5.

[3H] kH [H Donor] kH [3H][THF ds]
thus,
[3D] kD[THF- d] kD [3D][H Donor]

Equation 2-5. Competition methodology

The only reason a bimolecular process, as is the case here, can be expressed with such an

equation is that the concentration of hydrogen and deuterium donors are in great excess to

the radical precursor (at least 15 times for all cases). Although pseudo first order kinetic

requirements have been met, rate constants for the bimolecular processes are given as

second order. Scheme 2-6 gives an accurate picture of the competition experiments.









Exclusively from H-Donor


H-Donor
03SRfH 3H
hv kH
03SRfI h 03SRf
1 H20
STHF-d8
Radical Precursor kD O3SRfD 3D
kD

Exclusively from THF-dg


Scheme 2-6. Competition experiment

The competition experiments are usually performed using quartz NMR tubes as the

reaction vessels. Six samples with varied [H-Donor] concentrations and constant THF-d8

concentrations are added to the NMR tubes along with water and the radical precursor.

The total volume inside each NMR tube is kept constant through all experiments

(565 pL). To each NMR tube a capillary containing C6D6 as the lock solvent and CFC13

as the standard are added. The NMR tubes are degassed via three free-pump-thaw cycles,

and allowed to return to room temperature. The samples are then placed in a

photochemical UV reactor (254 nm) for 12 hours. Upon obtaining 19F NMR spectra for

each sample and careful integration of the product peaks, it is possible to obtain the

relative rate constants, kH / kD(THF-d8). Table 2-3 lists a sample of relative rate data.

The relative rate constants, kH/kD, are obtained by plotting the ratio of substrate

concentrations versus product ratios. A typical plot of [3H]/[3D] VS. [H-Donor]/[THF-ds]

is shown for THF in Figure 2-5. Values of kH/kD(THFd8) and the values of kH derived from

the known value of kD(THFd8) are collected in Table 2-4.









Table 2-3. Rate data for THF/THF-d8 competition towards -RfSO3Na Radical
[IRfSO3Na] [THF-ds] [THF]/ [3H]/3D a

(mol L1) (mol L1) [THF-ds]

0.013 1.29 0.204 1.67

0.013 1.28 0.415 3.47

0.013 1.28 0.605 5.03

0.013 1.28 0.809 6.68

0.013 1.30 0.990 7.40

0.013 1.28 1.22 9.99

a. all yields over 98%


THF vs THF-d8


y = 7.8714x + 0.1403
R2 = 0.9909


0 0.2


0.4 0.6 0.8
[THF]/[THF-d8]


1 1.2 1.4


Figure 2-5. Plot of [3H]/[3D] vs. [THF]/[THF-ds]

kHkD THF-d8 = Slope = 7.87 ( 0.38)

Intercept = 0.140 (0.296)









Table 2-4. Rate constants for H-atom abstractions
H-Donor kH/kD in H20 103 kH/M^s- a 103 kH/M s-1 b

in H20 n-C4F9- in BTB 63

CH30H 0.43 1.8 0.92

CH3CH20H 2.8 12 3.0

(CH3)2CHOH 11.4 48c 16

(CH20H)2 1.28 5.4

(CH3CHOH)2 5.6 24 5.0

CH3CO2CH20H 0.59 2.5

CF3CH20H 0.019 0.08

(CF3)2CHOH 0.094 0.39

THF 7.9 33d 31

(CH30CH2)2 1.3 5.5 6.7

CH3COCH3 0.015 0.06

CH3CO2H 0.005 0.02

CH3CH2CO2H 0.18 0.76

CH3CO2 Na 0.028 0.12

CH3CH2CO2 Na+ 0.36 1.5

HSCH2CH2SO3 Na+ 96 400

(HOCH2CH2CH2)3SiH 28 120

BrMe3N+CH2SiMe2H 20.5 86

H3P03 3.5 15

a. Based on kD = 4.2 x 103M-1 -1 b. From reference 55 c. LFP gave kH = 40 x 103 M1^s1

d. Value determined by LFP probe experiment and upon which all other rates are based









2.3 Discussion of the Kinetic Data

Before considering the kH rate constants in Table 2-4 it is imperative to establish

that the kH/kD ratios are not influenced by: (i) the small protic impurity in the (99.5%)

THF-ds, nor (ii) proton transfer from the water solvent to the fluoroalkyl radical. With

regard to (i), since kH/kD = 7.9 for THF/THF-ds, (Figure 2-5) plots of 3H/3D versus

[H-Donor]/[THF-ds] are expected to have a positive intercept, which will partially derive

from the H-content in the THF-ds. In a control experiment with THF-d8 alone, an

intercept of 7.9 x 0.5% = 0.04 was expected due simply to the H-content of the THF-ds.

This was confirmed when a 3H/3D ratio of 0.04-0.05 was observed. Therefore, non-zero

intercepts do not compromise the accuracy of the slopes of these plots, from which kH/kD

values are determined. The non-zero intercepts are a result of experimental error and the

small H-content in THF-ds. In regard to (ii), one can at least imagine that some 3D might

be replaced by 3H via an electron transfer from THF-d8 to -RfSO3 yielding a

perfluoroalkyl anion which would be rapidly protonated by water to yield 3H/3D ratios

which show a larger H-atom abstraction contribution, and would result in erroneous,

large 3H/3D ratios (Scheme 2-7).


d8 H20 \ d8

+ Na 03SCF2CF20CF2CF2 d / + Na 03SCF2CF20CF2CF2:



Na 03SCF2CF20CF2CF2: + Na 03SCF2CF20CF2CF2H

3H


Scheme 2-7. Possible electron transfer mechanism









The electron transfer reactions can be ruled out by the results described in (i) for THF-ds

alone in water yielding only the expected H-impurities. They were more firmly ruled out

by showing than no 3D was produced in a reaction carried out with THF in D20.

2.3.1 Rate Constants for H-Atom Abstractions in Water by Primary Fluoroalkyl Radicals

Rate constants for the eight alcohols show the expected response to structural

factors in terms both of C-H bond dissociation enthalpies (BDEs) and inductive effects.

Thus, the increase in kH along the series CH30H < CH3CH20H < (CH3)2CHOH

(Table 2-4) can be primarily attributed to a decrease in a-C-H BDEs along the series (94,

93, and 91 kcal mol-1, respectively). 81 Comparison of the rate constants for methanol,

ethanol, and isopropanol (1.8, 12, and 48 x 103 M1 s 1, respectively, Table 2-4) with

those reported for reaction of the CF3 radical with the same alcohols in water 82, 8, 46,

and 92 x 103 M1 s respectively, indicates that primary fluoroalkyl radicals are

somewhat less reactive than trifluoromethyl radicals in H-atom abstractions, a reactivity

difference which has been noticed previously for their additions to alkenes. 49 Rates of H-

atom abstraction from the P-CH position in alcohols are reduced by inductive electron

withdrawing (EW) neighboring atoms or groups because EW disfavors the polar effects

which can stabilize the transition state and, therefore, enhance the reactivity of a substrate

(see Figure 2-1). Thus, (CH20H)2 and (CH3CHOH)2 are only half as reactive,

respectively, as CH3CH20H and (CH3)2CHOH, despite having twice as many a-CH

hydrogen atoms. Even larger rate retarding polar effects are seen in the two

fluoroalcohols which are only 0.7-0.8% as reactive as their non-fluorinated counterparts

(Table 2-4).

Rate constants for H-atom abstraction from carbon are also small for compounds

containing EW carbonyl, ester, and carboxylic acid groups, some of which are so









unreactive that they may be suitable as solvents for chain reactions involving fluorinated

radicals. The carboxylate anions are more reactive than the corresponding carboxylic

acids. This result further suggests that polar effects play a role in stabilizing/destabilizing

the transition state. Mainly, any rate reduction due to coulombic repulsion between the

negative charges on the carboxylate anion and the radical's sulfonate group is more than

compensated for by the inductive electron donating ability of the CO2 group (C = -0.10

vs. cI = +0.34 for CO2H). 83

Not surprisingly, H-atom abstractions from ethers occur at rates comparable to the

rates of abstraction from alcohols. THF is six times as reactive towards -RfSO3 as

(CH30CH2)2. A six fold difference at -60 C 84 (dropping to a two fold difference at

27 C)85 has previously been reported for the rates of H-atom abstraction from THF and

(CH3CH2)20 by t-butoxyl radicals. The greater reactivity of THF was attributed to

favorable stereoelectronic effects factors in which conjugative electron delocalization

stabilizes the oxyalkyl radical reaction product and thereby decreases the C-H BDE in

THF relative to diethyl ether because of the small dihedral angle between the oxygen's

lone pair of electrons and the a-C-H bonds in THF.

The water-soluble thiol and two water-soluble silanes are sufficiently reactive

towards -RfSO3 that they may prove useful as chain transfer agents in fluoroalkyl radical

chain reactions.

2.3.2 Comparison of Rate Constants for H-atom Abstraction by Primary Fluoroalkyl
Radicals in Water and in BTB

The four alcohols for which the comparison is possible have kH values 2-5 times

greater in water than in BTB but the two ethers show no significant solvent effect on their

kH values. It has previously been reported that primary fluoroalkyl radicals add to the









C=C double bonds of styrenes 5-9 times and to 1-alkenes 3 times more rapidly in water

than in F 113. 48,73 It was concluded that these modest rate enhancements derived from

stabilization of the polar transition state for addition of the electrophilic fluorinated

radical to alkenes by the polar solvent, water. This is reasonable because the C=C double

bond of styrenes and alkenes are readily polarized and the developing negative and

positive charges in the transition state are well separated, and therefore can be solvated

by water molecules (Figure 2-6). This is not the case for a H-atom abstraction where any

charge separation occurs over a much shorter distance and the transition state is more

reminiscent of an intimate ion pair (Figure 2-1) than a solvent separated ion pair

(Figure 2-6).


SR- = R =-O3SCF2CF20 (H20)
R-CF2-CF2
= CF3 (F113)
6+
ruli/ ---- .,, yr ,,
rl r R = phenyl, n-alkyl

r = H, CH3, ect.



Figure 2-6. Charge separated polar transition state for addition to C=C double bonds

The absence of significant solvent effects on H-atom abstraction for hydrocarbons

by t-butoxyl radicals was first proposed by Walling and coworkers in the early 1960's

who observed that t-butanol/acetone product ratios, which reflect competition between H-

atom abstraction and P-scission of the t-butoxyl radical, showed large solvent effects

(Figure 2-7). 86-88














R-H kH




000
k,


Figure 2-7. Competing H-atom abstraction and P-scission pathways

It was argued that solvent interaction with the polar transition state for P-scission was

plausible, but the transition state for H-atom abstraction would be sterically crowded and

not allow solvation by the polar solvent. 86 Accordingly, the increased acetone formation

in polar solvents was attributed to solvationn of the transition state for the P-scission

process." 88 This analysis was proven correct 30 years later when direct, time resolved,

LFP kinetic measurements showed that there was no kinetic solvent effect on H-atom

abstraction from cyclohexane by t-butoxyl radicals. 89

The absence of a kinetic solvent effect on H-atom abstraction from hydrocarbons

by t-butoxyl radicals and its explanation provides a rationale for the rate constants for H-

atom abstraction from the two ethers by the fluoroalkyl radical in water and BTB being

essentially equal (Table 2-4).

However, the alcohols seem to show a modest 2-5 fold rate enhancement in water

vs. BTB for H-atom abstraction (Table 2-4). The observed accelerated rates may be due

to hydrogen bond formation between the hydroxyl group of the alcohol and a water

molecule (Figure 2-8).










H
5- 5+/
H o-H-- -O

C H


Figure 2-8. Hydrogen bonding of an alcohol to a water molecule

This will increase the electron density on the oxygen atom and stabilize the developing

radical center by conjugative electron delocalization, thus lowering the BDE of the

a-hydrogens and allowing for more rapid H-atom abstractions.

2.4 Conclusions

It was known that the rates of addition of fluorinated primary alkyl radicals to C=C

double bonds are larger by a factor of 3-9 in water than in a solvent of low polarity. 73

Now it has been discovered that the rates of H-atom abstraction by these radicals from

alcohols are only 2-5 times faster in water than in a low polarity solvent. Moreover, H-

atom abstraction form ethers is unaffected by solvent polarity, a result consistent with

earlier work on H-atom abstraction from hydrocarbons by t-butoxyl radicals. 86-89 Other

than the success of developing a method to obtain absolute rate constants for H-atom

abstractions by water soluble fluoroalkyl radicals, the final conclusion is that the

reactivities of these radicals can only be modulated to a minor extent by solvent polarity.

2.5 Experimental

All reagents used (including those of Table 2-4) were commercially available,

except for the two silanes 90 in Table 2-4, and were purchased from CIL, Adrich, Fisher,

or Lancaster. All reagents were used without further purification and all reaction solvents

were dried via known methods. NMR spectra and kinetic 19F NMR measurements were

performed at 282 MHz using a Varian VXR-300 spectrometer. All chemical shifts are









reported in ppm downfield from the internal standard, CFC13. 1H NMR spectra were

performed on the same instrument at 300 MHz, and chemical shifts are reported relative

to the internal standard, TMS. Melting points were determined using a Thomas Hoover

Capillary melting point apparatus.

2.5.1 Sodium 5-iodo-3-oxaoctafluoropentanesulfonate (1)

A solution of NaOH (2.9850g, 74.63 mmol) in 20 mL of deionized water was prepared

and stirred in a 100 mL round bottom flask equipped with a reflux condenser.

Tetrafluoro-2-(tetrafluoro-2-iodoethoxy)ethanesulfonyl fluoride (ICF2CF20CF2CF2SO2F,

15.8951g, 37.31 mmol) was added to the round bottom flask. The reaction mixture was

allowed to stir for 12 hours at 90 C. The water was removed by roto-evaporation,

yielding a white solid. Compound 1 (see appendix) was dissolved in absolute ethanol to

separate out the insoluble NaF. The ethanol was removed by roto-evaporation, and the

title compound was recrystallized from water to give a 90% yield: m.p. 149 C, dec.; 19F

NMR (D20/CFC13 in C6D6), 6 -67.81 (s, 2F), -82.08 (t, 2F, J = 12.1 Hz), -85.82 (s, 2F),

-117.90 (s, 2F).73

2.5.2 Sodium 4-(p-methyl)vinylbenzoate (2)

4-bromo-p-methylstyrene

A 3-neck round bottom flask was equipped with a pressure equalizing funnel, stir bar,

and a reflux condenser with nitrogen inlet. 100 mL of anhydrous THF along with ethyl-

triphenylphosphonium bromide (13.36g, 36 mmol) were charged to the flask and cooled

to -5 C. n-BuLi (2.5 M in hexane, 14.5 mL, 36 mmol) was slowly added to the stirred

solution via syringe resulting in a red solution which was stirred for 45 minutes. In a

flask, 4-bromobenzaldehyde (5.55g, 30 mmol) was dissolved in 50 mL of anhydrous

THF and added to the equalizing funnel. 4-bromobenzaldehyde was added drop wise









over about 1 hour, and allowed to achieve room temperature with stirring over night. The

reaction mixture was diluted with brine and extracted with three 100 mL portions of

benzene. The combined organic layers were dried with magnesium sulfate, and the

benzene was removed by roto-evaporation yielding an oily semi-solid. The oil was

dissolved in diethyl ether (50 mL) and the triphenylphosphonium oxide was filtered out.

After removal of the diethyl ether, the oil was purified by column chromatography using

hexanes as the mobile phase. The title compound was obtained as a colorless oil in 92%

yield: 1HNMR (CDC13, TMS), 8 7.37-7.44 (m, 2H), 7.14-7.20 (m,2H), [6.24-6.35 (m) +

5.82 (m)] (2H), 1.87 (m, 3H). 73

4-( P-methyl)vinylbenzoic acid

A 250 mL round bottom flask was equipped with a stir bar, and condenser with nitrogen

inlet. 4-bromo-P-methylstyrene (2.9g, 14.6 mmol) was dissolved in 70 mL of THF and

cooled to -78 C. The t-BuLi (1.7 M in pentane, 17.2 mL, 29.3 mmol) was slowly added

to the stirred solution via a syringe. The resulting dark green solution was stirred for 2

hours at -78 C. CO2 gas was then bubbled into the solution to saturation via a pipette.

The CO2 was generated by adding sodium carbonate to hydrochloric acid which was

dried by passing the gas through concentrated sulfuric acid and calcium sulfate. Upon

addition of the C02, the green color changed to a light brown, staw color. The solution

was allowed to achieve room temperature and stirred over night. The reaction mixture

was then acidified to pH = 2 with 10% HC1, and extracted three times with 30 mL

methylene chloride. The combined organic layers were dried with magnesium sulfate,

and the solvent was removed via roto-evaporation to give a white solid. The white solid

was recrystallized in ethyl acetate to give a 94% yield of the title acid: 1H NMR









(acetone-d6), 6 8.12-8.21 (m, 2H), 7.59-7.66 (m,2H), [6.54-6.65 (m) + 6.02 (m)] (2H),

2.02 (m,3H)73

Sodium 4-(p-methyl)vinylbenzoate (2)

4-( P-methyl)vinylbenzoic acid (1.0g, 6.17 mmol) was dissolved in 8 mL of methanol in a

1 neck round bottom flask. NaOH (1 M in methanol) was added until a pH of 7 was

obtained. The methanol was removed by roto-evaporation, and the resulting crystals

were washed and dried with diethyl ether. Compound 2 was obtained in 62% yield: 1H

NMR (D20), 6 8.00-8.11 (m, 2H), 7.45-7.56 (m, 2H), [6.41-6.49 (m)+ 5.93 (m)] (2H),

1.94 (m, 3H) 73

2.5.3 Sodium 5-H-3-oxaoctafluoropentanesulfonate (3)

ICF2CF20CF2CF2SO3Na-H20 (0.35g, .75 mmol) was added to a pyrex reaction vessel

along with 50 mL of THF. The solution was degassed by bubbling nitrogen for 30

minutes. The solution was then irradiated with UV for 24 hours. 19F NMR showed that

the radical precursor had disappeared. The excess THF was removed via roto-

evaporation to give a white solid. The white solid was washed with hexanes, then diethyl

ether, and dried under reduced pressure to give the title compound in 81% yield: 1H

NMR (acetone-d6), 6 6.48 (tt, 1H, J1 = 3.4 Hz, J2 = 52 Hz); 19F NMR (acetone-d6,

CFC13), 6 -81.6 (m, 2F), -88.7 (s, 2F), -117.6 (s, 2F), -138.2 (dt, 2F, J1 = 4.3 Hz, J2 = 51

Hz); HRMS 90 (FAB), (M + Na): calcd 342. 9263; found 342.9256. CHN 90

C4FsHNaO4S-H20: calcd C 14.21, H 0.89; found C 14.20, H 0.61%.

2.5.4 Kinetic Measurements by Time-Resolved Laser Flash Photolysis

The apparatus and procedures have been described elsewhere. 73,92 The radical, -RfSO3

was generated instantaneously by 308 nm LFP of aqueous solutions of the parent iodide

(1) at ambient temperature. 91









2.5.5 Verification of Probe Addition Rate Constant

The rate constant for addition, kadd, to the spectroscopic probe, 2, was obtained (duplicate

runs) in the usual manner to give values of (3.9 0.5) x 107 and (4.0 1.0) x 107 M-1 s1,

mean 3.95 x 107 M1 s-1, with a value of (3.3 0.3) x 107 M-1 s-1 reported previously. 73 In

any set of experiments, the probe's concentration was kept constant (Table 2-26) and

grow in of the absorption at 320 nm was monitored. 91

2.5.6 Laser Flash Photolysis Probe Experiments

The procedure has been described in detail previously. 48,79 1.5 mL of aqueous solutions

(0.027 M) of IRfSO3Na, 1, in quartz cuvettes (8 x 8 mm) sealed with rubber septa were

deaerated by flushing with N2 for 20 minutes, then the various amount (50-400 IL) of

deaerated THF or isopropanol and the volume of the sample was made up (when

necessary) to 2.0 mL. After addition of 100 [L of a stock solution (32.9 to 35.7 mM) of

2, the mixture was vortexed for 20 seconds and purged with nitrogen for a further 2-5

minutes. The growths of the optical density at 320 nm following each of 6 to 9 pulses of

308 nm laser were recorded for each concentration of H-atom donor. These growth

traces of the radical were analyzed by least squares fitting on the basis of psuedo-first-

order kinetics to obtain experimental rate constants, kexp. As described in the results, the

experimental rate constant is the sum of the rate constants for all competitive processes.79'

91

2.5.7 General Procedure for Kinetic Competition Studies

The kinetic studies were run in pyrex NMR tubes containing a sealed capillary tube

(CFC13 in C6D6) as the internal standard. For each kinetic study, a group of samples were

prepared at the same time. The NMR tubes were capped with rubber septa and wrapped

with Teflon tape before chemicals were added. The IRfSO3Na was used as a stock









solution (17.8% by weight) and added to the NMR tubes with a micro-syringe. All liquid

chemicals were added with syringes and weighed on a balance. The samples were

degassed by three freeze-pump-thaw cycles. After 19F NMR spectra were taken, the

samples were irradiated using a RPR-204 Rayonet photochemical reactor (254 nm). The

19F NMR were taken again after 24 hours. The NMR acquisition time was at least 15

minutes to assure accurate integration. The product ratios were obtained from the ratios

of integration of the CF2H and CF2D signals (see appendix). The conversion and yield

were obtained from the integration of the CF2I peak in the starting material and the

reduced product peaks relative to the internal standard. Tables and plots of kinetic data

are given in section 2.5.8.










2.5.8 Tables of Kinetic Data and Plots

Table 2-5. Rate data for THF/THF-d8 competition
[IRfSO3Na] [THF-ds] [THF]/[THF-d] [3H]/[3D] a

(mol L1) (mol L1)

0.013 1.29 0.204 1.67

0.013 1.28 0.415 3.47

0.013 1.28 0.605 5.03

0.013 1.28 0.809 6.68

0.013 1.30 0.990 7.40

0.013 1.28 1.22 9.99

a. all yields over 98%


THF vs THF-d8


y = 7.8714x + 0.1403
R2 = 0.9909


0 0.2 0.4 0.6 0.8
[THF]/[THF-d8]


1 1.2 1.4


Figure 2-9. Plot of [3H]/[3D] vs. [THF]/[THF-ds]

kHkD THF-d8 = Slope = 7.87 ( 0.38)

Intercept = 0.140 (0.296)

R2 = 0.991







42


Table 2-6. Rate data for CH30HTHF-d8 competition
[IRfSO3Na] [THF-ds] [CH30H]/[THF-ds] [3H]/3D a

(mol L-) (mol L1)

0.012 1.19 2.40 1.23

0.012 1.19 4.55 2.13

0.012 1.18 5.60 2.58

0.012 1.20 6.56 3.05

a. all yields over 98%


CH30H vs THF-d8


y = 0.4342x + 0.1733
R2 = 0.9989


0.5


0 -
1.5 2.5 3.5 4.5 5.5 6.5 7.5
[CH30H]/[THF-d8]



Figure 2-10. Plot of [3H]/[3D] VS. [CH30H]/[THF-ds]


kH/kD THF-d8


Slope = 0.434 (+ 0.010)


Intercept = 0.173 (0.051)


R2 = 0.999











Table 2-7. Rate data for CH3CH20H/THF-d8 competition
[IRfSO3Na] [CH3CH2OH]/ [CH3CH2OH]/[THF-ds] [3H]/[3D] a

(mol L1) (mol L1)


0.0108 .807 .735 2.54


0.0108 1.11 1.02 3.45


0.0108 1.57 1.44 4.72


0.0108 1.87 1.72 5.29


0.0108 2.15 1.95 6.00


0.0108 2.46 2.25 6.86


a. all yields over 98%


Ethanol vs THF-d8


75


65


55

5.o
-45


35


25


15
05 07 09 11 13 15 17 19
[EtOH]/[THF-d8]

Figure 2-11. Plot of [3H]/[3D] vs.[CH3CH2OH]/[THF-d8]

kH/kD = Slope = 2.81 (.069)

Intercept = .549 (.111)

R2 = .998


21 23 25


y=2805x+05487
R2 =0 9976










Table 2-8. Rate data for (CH3)2CHOH/THF-d8 competition
[IRfSO3Na] [(CH3)2CHOH] [(CH3)2CHOH]/ [3H]/3D] a

(mol L1) (mol L-1) [THF-ds]

0.0108 .138 .127 1.60

0.0108 .253 .229 2.94

0.0108 .356 .322 4.04

0.0108 .595 .541 6.43

0.0108 .706 .649 7.74

0.0108 .825 .753 8.78

a. all yields over 98%


Isopropanol vs THF-dS


0 01 2 03 04 05 D
IloptopanMijTHF-a l

Figure 2-12. Plot of [3H]/[3D] VS. [(CH3)2CHOH]/[THF-d8]

kH/kD = Slope = 11.4 (0.2)

Intercept = .270 (.086)

R2 = .999


y= 11 412x* 2699










Table 2-9. Rate data for ethylene glycol/THF-d8 competition
[IRfSO3Na] [THF-ds] [ethylene glycol]/ [3H]/[3D] a

(mol L1) (mol L-) [THF-ds]

0.012 1.20 0.313 0.557

0.012 1.22 0.607 0.963

0.012 1.20 0.913 1.38

0.012 1.19 1.33 1.97

0.012 1.19 1.76 2.47

0.012 1.19 2.35 3.16

a. all yields over 98%


Ethylene Glycol vs THF-d8


3.5
3
2.5
2
1.5
1
0.5
0


0 0.5 1 1.5
[Ethylene Glycol]l[THF-d8]


y= 1.2825x + 0.1954
R2 = 0.998


2 2.5


Figure 2-13. Plot of [3H]/[3D] VS. [ethylene glycol]/[THF-ds]

kH/kD THF-d8 = Slope = 1.28 ( 0.03)

Intercept = 0.195 (0.040)

R2 = 0.998










Table 2-10. Rate data for 2,3-butanediol/THF-d8 competition
[IRfSO3Na] [THF-ds] [2,3-butanediol]/ [3H]/[3D] a

(mol L-) (mol L-) [THF-ds]

0.013 1.33 0.162 1.23

0.013 1.33 0.348 2.36

0.013 1.33 0.524 3.42

0.013 1.33 0.696 4.58

0.013 1.33 0.870 5.21

0.013 1.32 1.05 6.14

a. all yields over 98%


2,3-Butanediol vs THF-d8


y = 5.5469x + 0.449
R2 = 0.9933


0 0.2 0.4 0.6 0.8
[2,3-Butanediol]/[THF-d8]


1 1.2


Figure 2-14. Plot of [3H]/[3D] vs. [2,3-butanediol]/[THF-ds]

kH/kD THF-d8 = Slope = 5.55 ( 0.23)

Intercept = 0.449 (0.155)

R2 = 0.993










Table 2-11. Rate data for methyl glycolate/THF-ds competition
[IRfSO3Na] [THF-ds] [methyl glycolate]/ [3H]/[3D] a

(mol L-) (mol L-) [THF-ds]

0.011 1.19 0.405 0.450

0.011 1.20 0.816 0.804

0.011 1.21 1.24 1.15

0.011 1.19 2.09 1.66

0.011 1.17 3.04 2.14

0.011 1.17 4.33 2.83

a. all yields over 98%


Methyl Glycolate vs THF-d8


3.5
3
2.5
S2
I
1.5
1
0.5
0


1 2 3 4
[Methyl Glycolate]/[THF-d8]


Figure 2-15. Plot of [3H]/[3D] VS. [methyl glycolate]/[THF-ds]

kH/kD THF-d8 = Slope = 0.593 ( 0.028)

Intercept = 0.328 (0.067)

R2 = 0.991


y = 0.5927x + 0.328
R2 = 0.9912










Table 2-12. Rate data for CF3CH20H/THF-d8 competition
[IRfSO3Na] [THF-ds] [ CF3CH20H] [3H]/3D a

(mol L-1) (mol L-1) [THF-ds]

0.011 0.232 4.27 0.158

0.011 0.223 6.69 0.203

0.011 0.223 8.82 0.260

0.011 0.221 11.1 0.286

0.011 0.218 14.6 0.348

0.011 0.218 17.9 0.421

a. all yields over 98%


CF3CH20H vs THF-d8


0.45
0.4
0.35
S0.3
, 0.25
0.2
0.15
0.1


13
[CF3CH20H]I[THF-8]


Figure 2-16. Plot of [3H]/[3D] vs. [CF3CH2OH]/[THF-ds]

kHkD THF-d8 = Slope = 0.0188 ( 0.0007)

Intercept = 0.0803 (0.0085)

R2 = 0.994


y = 0.0188x + 0.0803
R2 = 0.9939










Table 2-13. Rate data for (CF3)2CHOH/CD30D competition
[IRfSO3Na] [CD30D] [(CF3)2CHOH]/ [3H]/[3D a

(mol L1) (mol L-) [CD30D]

0.011 2.20 0.314 0.121

0.011 2.16 0.473 0.472

0.011 2.20 0.617 0.872

0.011 2.18 0.779 1.30

0.011 2.19 0.971 1.87

0.011 2.19 1.16 2.11

a. all yields over 98%


(CF3)2CHOH vs CD30D


2.5

2

S1.5

2. 1

0.5

0


0.2 0.4 0.6 0.8 1 1.2 1.4
[(CF3)2CHOH]/[CD30D]



Figure 2-17. Plot of [3H]/[3D] VS. [(CF3)2CHOH]/[CD30D]

kH/kD CD30D = Slope = 2.47 ( 0.12)

Intercept = -0.651 (0.093)

R2 = 0.991


y = 2.4685x 0.6507
R2 = 0.9906










Table 2-14. Rate data for CH30CH2CH2OCH3/THF-d8 competition
[IRfSO3Na] [THF-d8] [(CH30CH2)2]/ [3H]/[3D a

(mol L1) (mol L1) [THF-d8]

0.011 1.07 0.414 0.792

0.011 1.06 0.807 1.35

0.011 1.07 1.18 1.88

0.011 1.07 1.58 2.35

0.011 1.07 1.95 2.82

0.011 1.06 2.34 3.35

a. all yields over 98%


CH30CH2CH20CH3 vs THF-d8


4
3.5
3
2.5
S2
1.5
1
0.5
0


y = 1.3128x + 0.2806
R2 = 0.9991


0 0.5 1 1.5 2
[CH30CH2CH20CH3]I[THF-d8]


Figure 2-18. Plot of [3H]/[3D] vs. [CH3OCH2CH20CH3]/[THF-ds]

kH/kD THF-d8 = Slope = 1.31 (0.02)

Intercept = 0.280 (0.030)

R2 = 0.999










Table 2-15. Rate data for (CH3)2CO/THF-d8 competition
[IRfSO3Na] [THF-ds] [(CH3)2CO]/ [3H]/[3D a

(mol L1) (mol L-) [THF-ds]

0.012 1.19 2.39 0.0953

0.012 1.19 3.57 0.117

0.012 1.19 4.46 0.126

0.012 1.19 5.65 0.144

a. all yields over 98%


Acetone vs THF-d8


0.15
0.14
0.13
S0.12
S0.11
0.1
0.09
0.08


y = 0.0146x + 0.0619
R2 = 0.99


3 4 5
[Acetone]/[THF-d8]


Figure 2-19. Plot of [3H]/[3D] vs. [(CH3)2CO]/[THF-d8]

kH/kD THF-d8 = Slope = 0.0146 ( 0.0010)

Intercept = 0.0619 (0.0043)

R2 = 0.990










Table 2-16. Rate data for CH3COOH/THF-d8 competition
[IRfSO3Na] [THF-ds] [Acetic Acid]/ [3H]/[3D] a

(mol L1) (mol L-) [THF-ds]

0.012 1.18 3.10 0.0542

0.012 1.19 4.45 0.0589

0.012 1.20 5.76 0.0676

0.012 1.19 7.23 0.0685

0.012 1.19 8.60 0.0756

0.012 1.18 10.0 0.0881

a. all yields over 98%


Acetic Acid vs THF-d8


0.1

0.09

0.08

S0.07

0.06

0.05

0.04


y = 0.0046x + 0.0391
R2 = 0.9483


2 4 6 8
[Acetic Acid]/[THF-d8]


10 12


Figure 2-20. Plot of [3H]/[3D] vs. [CH3COOH]/[THF-ds]

kH/kD THF-d8= Slope = 0.00455 ( 0.00053)

Intercept = 0.0391 (0.0037)

R2 = 0.948










Table 2-17. Rate data for CH3COONa/THF-ds competition
[IRfSO3Na] [THF-ds] [CH3COONa]/ [3H]/[3D] a

(mol L1) (mol L1) [THF-d8]

0.011 0.214 3.53 0.182

0.011 0.217 4.62 0.225

0.011 0.217 5.78 0.277

0.011 0.217 6.94 0.308

0.011 0.214 9.70 0.381

0.011 0.212 12.2 0.431

a. all yields over 98%


CH3COONa vs THF-d8


0.5
0.45
0.4
S0.35
S0.3
0.25
0.2
0.15
0.1


2 4 6 8 10
[CH3COONa]/[THF-d8]


y = 0.0284x + 0.0985
R2 = 0.9793


12 14


Figure 2-21. Plot of [3H]/[3D] VS. [CH3COONa]/[THF-ds]

kH/kD THF-d8 = Slope = 0.0284 ( 0.0020)

Intercept = 0.0985 (0.0159)

R2 = 0.979










Table 2-18. Rate data for CH3CH2COOH/THF-d8 competition
[IRfSO3Na] [THF-ds] [CH3CH2COOH]/ [3H]/[3D] a

(mol L1) (mol L-) [THF-ds]

0.012 1.20 1.48 0.382

0.012 1.20 2.55 0.534

0.012 1.20 3.61 0.749

0.012 1.20 4.66 0.923

0.012 1.19 5.82 1.16

a. all yields over 98%


CH3CH2COOH vs THF-d8


1.4

1.2

1

0.8
I
0.6

0.4

0.2


y = 0.1804x + 0.0959
R2 = 0.9968


1 2 3 4 5
[CH3CH2COOH]/[THF-d8]


6 7


Figure 2-22. Plot of [3H]/[3D] vs. [CH3CH2COOH]/[THF-ds]

kH/kD THF-d8 = Slope = 0.180 ( 0.006)

Intercept = 0.0959 (0.0234)

R2 = 0.997











Table 2-19. Rate data for CH3CH2COONa/THF-d8 competition
[IRfSO3Na] [THF-ds] [CH3CH2COONa]/ [3H]/[3D] a

(mol L1) (mol L1) [THF-ds]

0.013 1.28 0.288 0.181

0.013 1.29 0.484 0.265

0.013 1.29 0.778 0.373

0.013 1.29 1.13 0.464

0.013 1.28 1.42 0.610

a. all yields over 98%


CH3CH2COONa vs THF-d8


0.7
0.6
0.5
S0.4-
S0.3
0.2
0.1
0
0


y = 0.3617x + 0.082
R2 = 0.9902


0.5 1
[CH3CH2COONa]/[THF-d8]


Figure 2-23. Plot of [3H]/[3D] VS. [CH3CH2COONa]/[THF-ds]

kH/kDoTHF-d8 = Slope = 0.362 ( 0.021)

Intercept = 0.0820 (0.0190)

R2 = 0.990










Table 2-20. Rate data for HSCH2CH2SO3Na/THF-d8 competition
[IRfSO3Na] [THF-ds] [HSCH2CH2SO3Na]/ [3H]/[3D] a

(mol L1) (mol L1) [THF-ds]

0.011 0.677 0.174 20.1

0.011 0.677 0.232 27.3

0.011 0.675 0.291 29.1

0.011 0.673 0.349 38.9

0.011 0.675 0.408 41.0

0.011 0.682 0.460 48.7

a. all yields over 98%


HSCH2CH2SO3Na vs. THF-d8


55
50
45
40
35
30
25
20
15
10
0.13


y = 96.045x + 3.5449
R2 = 0.9723


0.23 0.33 0.43
[HSCH2CH2SO3Na]/[THF-d8]


0.53


Figure 2-24. Plot of [3H]/[3D] vs. [HSCH2CH2SO3Na]/[THF-ds]

kH/kD THF-d8 = Slope = 96.0 ( 8.1)

Intercept = 3.54 (2.70)

R2 = 0.972











Table 2-21. Rate data for (HOCH2CH2CH2)3SiH/THF-d8 competition
[IRfSO3Na] [THF-ds] [Silane]/ [3H]/[3D] a

(mol L-) (mol L1) [THF-d] b

0.0079 0.487 0.131 3.46


0.0079 0.479 0.160 4.04

0.0079 0.483 0.185 5.12

0.0079 0.485 0.211 5.74

0.0079 0.489 0.261 7.02

a. all yields over 98%; b. reference 90


(HOCH2CH2CH2)3SiH vs THF-d8


7.5
7
6.5
6
" 5.5
S5
. 4.5
4
3.5
3
2.5-
0.1


y = 28.135x 0.2583
R2 = 0.9898


0.15 0.2 0.25
[(HOCH2CH2CH2)3SiH]/[THF-d8]


Figure 2-25. Plot of [3H]/[3D] VS. [(HOCH2CH2CH2)3SiH]/[THF-ds]

kH/kD THF-d8 = Slope = 28.1 ( 1.6)

Intercept = -0.258 (0.321)

R2 = 0.990










Table 2-22. Rate data for Me3N CH2SiMe2H Br-/THF-d8 competition
[IRfSO3Na] [THF-ds] [Silane]/ [3H]/[3D] a

(mol L1) (mol L1) [THF-ds] b

0.011 0.655 0.0673 1.01

0.011 0.671 0.164 3.05

0.011 0.662 0.333 6.85

0.011 0.672 0.492 9.63

a. all yields over 98%; b. reference 90


BrMe3NCH2SiMe2H vs THF-d8


12

10

8

6

4

2

0


0 0.1 0.2 0.3 0.4 0.5
[BrMe3NCH2SiMe2H]/[THF-d8]

Figure 2-26. Plot of [3H]/[3D] vs. [BrMe3NCH2SiMe2H]/[THF-ds]

kH/kD THF-d8 = Slope = 20.5 ( 0.8)

Intercept = -0.283 (0.245)

R2 = 0.997


y = 20.516x 0.2827
R2 = 0.997










Table 2-23. Rate data for H3PO3/THF-d8 competition
[IRfSO3Na] [THF-d] [H3PO3]/ [3H]/[3D] a

(mol L1) (mol L-) [THF-ds]

0.011 1.08 0.271 1.73

0.011 1.09 0.536 2.79

0.011 1.09 0.804 3.68

0.011 1.09 1.07 4.79

0.011 1.09 1.34 5.46

0.011 1.09 1.61 6.43

a. all yields over 98%


H3P03 vs. THF-d8


y = 3.4796x + 0.8811
R2 = 0.9964


1
[H3PO3]/[THF-d8]


Figure 2-27. Plot of [3H]/[3D] vs. [H3PO3]/[THF-d8]

kH/kD THF-d8 = Slope = 3.48 ( 0.10)

Intercept = 0.881 (0.109)

R2 = 0.996









Table 2-24. Rate constants (kgl) for RfSO3- + 4-(1-propenyl)benzoate Na 2, in water
[2] / M kex [2] kex

/ S-1 / M / s-1

4.43 x 10-3 2.00 x 105 5.89 x 10-3 2.38 x 105

3.64x 10-3 1.38 x 10 4.16 x103 1.81 x 105

2.82 x 10-3 1.15 x 105 3.21 x 103 1.32 x 105

1.94x 10-3 1.09 x105 2.21 x103 1.08 x105

1.38 x 10-3 6.53 x 104 1.68 x 10-3 7.27 x 104

9.99 x 10-4 4.61 x 104


slopea= 3.96 x 107 M1 S1

R2= 0.9313

std err slope = 5.4 x 106

confidence interval b=1.0 x 107


slope a= 3.86 x 107 M^1 -1

R2 = 0.9882

standard err slope = 2.4 x 106

confidence interval b=4.9 x 106


kg = (4.0 1.0) x 107 M1 -1 kl = (3.9 0.5) x 107 M-s1

a. slope of the plot of kex vs. [2], example Figure 2-2 in text. b. 90% confidence level.









Table 2-25. LFP kinetic probe data yielding kH for THF
[THF] kex [2] kex kg [2]

/M /s-1 /M /s-1

Entry 1

0.000 6.23E+04 1.57E-03 2.03E+03

0.184 7.13E+04 1.57E-03 1.10E+04

0.367 8.49E+04 1.57E-03 2.47E+04

0.730 9.56E+04 1.57E-03 3.54E+04

1.470 1.22E+05 1.57E-03 6.12E+04


slope a =3.9E+04

R2 = 0.9800

std err slope= 3.2E+03

confidence interval b = 6.5E+03

kH = (3.9 0.7)x 104 M-ls-









Table 2-25. Continued:

Entry 2

0.000 7.04E+04 1.70E-03 5.10E+03

0.129 7.35E+04 1.70E-03 8.22E+03

0.194 7.96E+04 1.70E-03 1.43E+04

0.290 7.99E+04 1.70E-03 1.47E+04

0.436 8.39E+04 1.70E-03 1.86E+04

0.653 8.96E+04 1.70E-03 2.43E+04

0.980 1.04E+05 1.70E-03 3.85E+04

1.470 1.18E+05 1.70E-03 5.24E+04


slope a= 3.2E+04

R2 = 0.9907

std err slope = 1.3E+03

confidence interval b = 2.4E+03

kH = (3.2 0.2) x 104 M-ls









Table 2-25. Continued:

Entry 3

0.000 8.33E+04 1.68E-03 1.89E+04

0.194 8.93E+04 1.68E-03 2.49E+04

0.290 9.22E+04 1.68E-03 2.78E+04

0.653 9.76E+04 1.68E-03 3.32E+04

0.980 1.14E+05 1.68E-03 5.00E+04

1.470 1.35E+05 1.68E-03 7.06E+04


slope a= 3.45E+04

R2= 0.9707

std err slope = 3.0E+03

confidence interval b = 5.8E+03

kH = (3.5 + 0.6) x 104 M-1s









Table 2-25. Continued:

Entry 4

0.000 6.69E+04 1.62E-03 4.79E+03

0.201 7.66E+04 1.62E-03 1.45E+04

0.301 8.08E+04 1.62E-03 1.87E+04

0.452 8.44E+04 1.62E-03 2.23E+04

0.678 8.93E+04 1.62E-03 2.72E+04

1.016 9.92E+04 1.62E-03 3.71E+04

1.524 1.12E+05 1.62E-03 4.99E+04

2.287 1.39E+05 1.62E-03 7.66E+04

2.940 1.51E+05 1.62E-03 8.86E+04


slope a 2.8E+04

R2= 0.9938

std err slope = 8.5E+02

confidence interval b =1.6E+03

kH = (2.8 0.2) x 104 M-ls-









Table 2-25. Continued:

entry 5

0.000 7.62E+04 1.70E-03 1.10E+04

0.201 7.94E+04 1.70E-03 1.42E+04

0.301 8.70E+04 1.70E-03 2.18E+04

0.452 9.30E+04 1.70E-03 2.78E+04

0.677 9.45E+04 1.70E-03 2.93E+04

1.016 1.13E+05 1.70E-03 4.78E+04

1.524 1.30E+05 1.70E-03 6.48E+04

2.940 1.67E+05 1.70E-03 1.02E+05



slope = 3.2E+04

R2= 0.9876

std err slope = 1.5E+03

confidence interval b = 2.7E+03

kH = (3.2 0.3) x 104 M-ls

a. slope of kexp vs. [THF], an example plot is given in Figure 2-3 in the text.

b. 90% confidence interval.









Table 2-26. LFP kinetic probe data yielding kH for isopropanol
[H-donor] kex [2] kex kg [2]

/M /s-1 /M /s-1

Entry 1

0.000 4.96E+04 1.40E-03 4.39E+03

0.478 6.56E+04 1.40E-03 1.17E+04

0.720 8.26E+04 1.40E-03 2.87E+04

1.080 9.47E+04 1.40E-03 4.07E+04

1.610 1.22E+05 1.40E-03 6.79E+04

2.420 1.46E+05 1.40E-03 9.19E+04

3.110 1.76E+05 1.40E-03 1.22E+05




Entry 2

0.000 7.20E+04 1.76E-03 4.07E+03

0.478 8.82E+04 1.76E-03 2.03E+04

0.720 9.88E+04 1.76E-03 3.09E+04

1.080 1.03E+05 1.76E-03 3.51E+04

1.610 1.22E+05 1.76E-03 5.41E+04

2.420 1.66E+05 1.76E-03 9.81E+04

3.110 1.94E+05 1.76E-03 1.26E+05









Entry 1:

slope a = 4.09E+04

R2 = 0.9945

std err slope = 1.2E+03

confidence interval b = 2.3E+03

kH = (4.1 0.2)x 104 M-ls-

Entry 2:

slope a= 3.95E+04

R2= 0.9839

std err slope = 2.3E+03

confidence interval b = 4.3E+03

kH = (3.9 0.4)x 104 M-ls-


a. slope of kexp vs. isopropanoll], an example plot is given in Figure 2-3 in the text.

b. 90% confidence interval.















CHAPTER 3
RATE CONSTANTS FOR OXYANION ACCELERATED HYDROGEN
ABSTRACTION REACTIONS FROM ALKOXIDES BY A PERFLUOROALKYL
RADICAL IN WATER

3.1 Introduction

Shortly after Evans discovered huge rate accelerations exhibited by anionic oxy-

Cope rearrangements (Figure 3-1), 93,94 it was hypothesized that such accelerations were

related to the bond weakening effect of the anionic alkoxy group on the adjacent C3-C4

bond. 95


HO HO

O Oxy-Cope rearrangement





+-
Mo M

O Anionic oxy-Cope rearrangement




Anionic rate enhancement of 101o1017 !

Figure 3-1. Anionic oxy-Cope rearrangement rate enhancement

This basic conclusion from Goddard's GVB theory work has recently been confirmed

and elaborated on by Houk 96 and Baumann 97 using density functional theory

methodology. Houk has determined that the C-H BDE of methoxide ion is -23 kcal less

than that of methanol. 96 The a-C-H bond weakening effect observed for alkoxides should









provide acceleration to other reactions that involve the breaking of this same bond. Many

such cases have been reported, 98 such as alkoxy accelerated [1.3]-sigmatropic

rearrangements, 99, 100 the Ireland Claisen rearrangement of allyl ester enolates, 101 and

1,5-hydrogen shifts. 102

In chapter two, competition methods using 19F NMR were employed to obtain the

absolute rate constants for hydrogen atom abstraction for many organic hydrogen donors.

As shown in Figure 3-2, isopropanol is fairly reactive towards perfluoroalkyl radicals in

both the non-polar solvent 1,3-bis-trifluoromethylbenzene (BTB) and in water. Modest

rate enhancement is observed in water due to probable hydrogen bonding interactions

between water and the hydroxyl group weakening the C-H BDE.


H OH o OH
/\ / 25 C, solvent /
R + C RfH + C



Rf. Solvent kH

CF3CF2CF2CF2 BTB 1.6 x 104 M-1 -1

03SCF2CF20CF2CF2 H20 4.8 x 104 M-1 s-1


Figure 3-2. Isopropanol reactivities in BTB and water

Although polar, steric, and thermodynamic effects can have dramatic effects on the

H-abstraction rates from organic compounds by fluorinated radicals, when working with

a series of similar compounds, the relative rates of H-abstraction by

03SCF2CF20CF2CF2- (4) correlate well with their relative C-H BDEs, as shown for the

series of alcohols in water. The bond dissociation energies of methanol, ethanol, and

isopropanol in Table 3-1 were estimated by computational methods. 103









Table 3-1. Correlation between rate constant and calculated a-C-H BDEs
Alcohol kH / 103 M-1 s1 krei (Per H) BDE's / kcal mol1

CH30H 1.8 (1) 93

CH3CH20H 12 10 91

(CH3)2CHOH 48 80 89



As a result of the observed importance of BDEs on the abstraction of hydrogen

atoms by perfluoroalkyl radicals and the many reported cases of C-H bond weakening

effects of alkoxides, it was determined that the quantitative impact of the effects of

alkoxide functional groups warranted investigation. The only related previous work

reported is that of Bunnett in which he found that methoxide ion was a good hydrogen

atom donor to aryl radicals, 104, 105 being about 45 times more reactive than methanol for

donation of a hydrogen atom to the p-nitrophenyl radical. 106

An immediate concern which arises in carrying out kinetic studies of hydrogen

abstraction from alkoxides is that the alkoxide substrate must be present in the

competition mixture as a totally homogeneous solute, something that is impossible in

both BTB and the aqueous medium, the latter because the basicities of alkoxides would

preclude their existence in water. However, as part of the investigation into hydrogen

atom abstraction by fluorinated radicals from alcohols in water, the absolute rate

constants for H-atom abstraction from trifluoroethanol and hexafluoroisopropanol have

been determined. Due to the polar and electrostatic influence of fluorine substituents,

these two fluorinated alcohols were many orders of magnitude less reactive than their

hydrocarbon counterparts (Table 3-2).









Table 3-2. Rate constants for hydrogen abstraction from fluorinated and non-fluorinated
alcohols
Alcohol kH/ 103 M^1 s- krel

CH3CH20H 12 hydrocarbon 150 times

CF3CH20H 0.08 more reactive

(CH3)2CHOH 48 hydrocarbon 123 times

(CF3)2CHOH 0.39 more reactive



However slow the kinetics of these fluorinated alcohols may be towards hydrogen

abstraction, they have one property which was extremely propitious in view of the afore

mentioned interest in probing the kinetics of H-atom abstractions from alkoxides.

Mainly, they are much more acidic than their non-fluorinated counter parts, having pKa's

of 12.4 and 9.3 for trifluoroethanol and hexafluoroisopropanol, respectively. 107 Their

conjugate bases, the alkoxides, would therefore be relatively weak, stable, and

homogeneously soluble in water.

3.2 Results and Discussion

3.2.1 Kinetic Results

Relative rate constants (kH/kD) for H-atom abstraction by 03SCF2CF20CF2CF2'

(4) from sodium trifluoroethoxide (TFEO, 5), sodium hexafluoroisopropoxide

(HFIPO, 6), and sodium trifluoroisopropoxide (TFIPO, 7), were first determined by

competition kinetics involving H-transfer from the alkoxide versus D-transfer from

THF-ds (Scheme 3-1). The same general procedure was described in detail previously in

Chapter 2. The relative rate constants were easily converted to absolute rate constants

using the value of THF-ds's known rate constant, kD = 4.2 x 103 M1 s', which was

previously determined using laser flash photolysis. The results obtained demonstrated









that all three alkoxides are not only very much more reactive than their respective

alcohols, but that they are also considerably more reactive than the corresponding non-

fluorinated alcohols (Table 3-3).

exclusively from CF3CH20
5 r
CF3CH20 -
-H- 03SRfH 3H 19FNMR -138.3 ppm(dt)

hv H20
03SRfI hH2 3SR
THF-d8 4
CF3CH20 -~D -03SRfD 3D 19FNMR = -139.0ppm(m)
5 kD
exclusively from THF-d8

Scheme 3-1. Competition scheme showing trifluoroethoxide (5) and THF-ds

Table 3-3. Absolute rate constants for alkoxides and corresponding alcohols
Alkoxide/Alcohol kH / 103 M1 s1 krel

CF3CH20 Na+ (5) 77 alkoxide 963 times

CF3CH20H 0.08 more reactive

(CF3)2CHO Na+ (6) 108 alkoxide 277 times

(CF3)2CHOH 0.39 more reactive

(CF3)(CH3)CHO Na (7) 155 alkoxide 103 times

(CF3)(CH3)CHOH 1.5 more reactive



This high reactivity undoubtedly derives from a combination of the bond-weakening

effect of the alkoxide functional group and the enhanced nucleophilicity of the alkoxide

C-H bond towards the highly electrophilic perfluoro radical.

LFP measurements were used to verify the observed results in the competition

experiments for alkoxides. The LFP measurements of the rate constants for H-atom









abstraction by 03SCF2CF20CF2CF2' from TFEO (5) and HFIPO (6) met with mixed

success. For TFEO the LFP value of kH was 11 x 104 M-1 s1, which is in reasonable

agreement with the 7.7 x 104 M-1 s-1 obtained by competition, as reported in Table 3-3.

However, for HFIPO the observed LFP kH was 50 x 104 M-1 s1, which is 4.5 times

greater than the competition value of 11 x 104 M-1 s1. The reasoning for the

contradiction in rate values for HFIPO may rest in the fact that both H-bonding and ion

pairing (with the metal counterion) are known to cause large variations in alkoxide

accelerated rate constants. 100 Other kinetic results seem to show that alkoxide accelerated

processes are very sensitive to anything which influences the degree of free charge on the

alkoxide. 93 As a result of this contradiction of rate constants for HFIPO, additional

competition experiments were designed to validate the competition method for this

system.

First a direct competition between the two alkoxides using sodium 2-deuterio-

hexafluoroisopropoxide (8) in competition with sodium trifluoroethoxide (TFEO, 5), with

no THF being involved was carried out. (Scheme 3-2).


5 03SRfH 3H
O3SRf. + H20
4
(CF3)2CDO 03SRfD 3D
8

No THF-d8 involved


Scheme 3-2. Competition with no THF-ds

Combining this measured kH/kD value (4.64) with the value of the primary isotope effect

(kH/kD = 5.88) for H- vs. D- abstraction from HFIPO, and using the rate constant of









7.7 x 104 M-1 s-1 for TFEO hydrogen abstraction, yields a rate constant (kH) for HFIPO of

9.8 x 104 M 1 s-1 (Equation 3-1).


kH(TFEO) kH(HFIPO)
= 4.64 = 5.88
kD(HFIPO-d) kD(HFIPO-d)


and kH(TFEO) = 7.7 x 104 M-1s1 ; therefore

7.7 x 104 M-s-1
kD(HFIPO-d) =
4.64

kD(HFIPO-d)= 1.66x 104 M-1s1; andusing 5.88

kH(HFIPO) = 9.8 x 104 M-s-1

Equation 3-1. Calculation of kH (HFIPO) without using THF-ds

Secondly, a "reverse" competition experiment was carried out, using deuterated

HFIPO (8) and undeuterated THF. This gave a kH/kD value of 1.94, which when

combined with the kH value for THF (3.3 x 104 M 1 S-1) and the HFIPO isotope effect

(kH/kD = 5.88) provides a value of kH for HFIPO of 10 x 104 M-1 s-1 (Equation 3-2).

kH(THF) kH(HFIPO)
= 1.94 ; = 5.88
kD(HFIPO-d) kD(HFIPO-d)


and kH(THF) = 3.3 x 104 M-1-1 ; therefore

3.3 x 104 M-is-
kD(HFIPO-d) =
1.94

kD(HFIPO-d)= 1.70x 104 M-1s1; andusing 5.88

kH(HFIPO) = 10.0 x 104 M-1-1
Equation 3-2. Calculation of kH (HFIPO) using a "reverse" competition









There is therefore a self consistency in the values of kH for HFIPO that were obtained

from the three different competition studies (11, 9.8, and 10 x 104 M-1 s-1), and we feel

confident that their average, 10.8 x 104 M-1 S1, can be regarded as a reliable value for the

kH of HFIPO.

Aldehyde hydrates and their monosodium salts are also of interest and relevant to

the present work because they can be regarded as a-hydoxy-substituted alcohols and

alkoxides. Again, in order to study such compounds in water, one must have aldehyde

hydrates that exist virtually 100% in the hydrate form when in water, and are acidic

enough that their monobasic forms are stable in water. Chloral and fluoral hydrate meet

these requirements nicely because the presence of the three 0-chlorines or fluorines

insures that the hydrates are exclusively present in water, and that they are sufficiently

acidic enough to cleanly form their monosodium salts upon treatment with one equivalent

of NaH (Scheme 3-3).

O Na+


CC13CH(OH)2 + 1.0 eq. NaH die l C OH

pKas8 = 10.1 C H

diethyl ether o Na
CF3CH(OH)2 + 1.0 eq. NaH 1
o __ 10
pKa108 = 10.2 C F3C OH

H

Scheme 3-3. Preparation of the monobasic sodium salts

In fact the pKa's of chloral and fluoral hydrate have been estimated to be 10.1 and 10.2,

respectively. 108 Because the inductive effect of the three P-halogens destabilizes the

transition state, these hydrates, like fluorinated alcohols, should be poor H-atom donors










to 03SCF2CF20CF2CF2-. This is the case as shown in Table 3-4, which shows that

chloral hydrate is slightly more reactive than fluoral hydrate, which slightly more reactive

than trifluoroethanol, results which are consistent with stabilization of the carbon

centered radicals formed from the hydrates by the extra a-hydroxy group. More

significantly, the monosodium salt of fluoral hydrate exhibits the largest enhancement,

relative to its non-alkoxy counterpart (kre = 1315), as well as the largest rate constant that

has yet to be observed for H-atom abstraction from carbon to the fluorinated radical,

O3SCF2CF20CF2CF2- (kH = 1.7 x 105 M-1 s-1).

Table 3-4. Absolute rate constants of hydrates and monobasic hydrate anions
Hydrate /

Hydrate monoanion kH / 103 M-1 s-1 krel

CCl3CH(OH)2 0.83



oNa+ 157 189

C13C-- OH 9

H

CF3CH(OH)2 0.13



0Na 171 1315

F3C- OH 10

H

CF3CH20H 0.08









3.2.2 Possible Synthetic Applications

As mentioned in the introduction to chapter one, chemists have been interested in

developing synthetically useful free radical reactions. However, there has not been much

attention paid to utilizing fluorinated free radical intermediates in synthesis. Such

synthetic efforts so far have been reported by Paleta. 109 He has shown that by taking

advantage of low BDEs of mainly alcohols and ethers, one can initiate nucleophilic

radical additions by UV irradiation and further improve yields through the use of a photo-

sensitized process involving acetone (Figure 3-3) 109


0__ CH2CH2-C6F13
hv OH CH3
acetone
CH3CHCH3 CH3CCH2-CH2-C6F13

CH2=CH-C6Fi3 OH
OH
CH3CH20H
hv r-\ CH2-C-CH2CH-C6F13
acetone 0O CH2CH2C 6F13
00


Figure 3-3. Photo-sensitized addition of alcohols and cyclic ethers

The yields for the reactions in Figure 3-3 are all 90-97%, which indicates a very good

chain process. It is worth noting that all of Paleta's additions are to electron deficient

olefins, probably to better match the SOMO-LUMO energy gap.

We found the possibility of using CF3CH(OH)O (10) in Paleta's radical chain

process intriguing because adding CF3 groups via alkene addition would be synthetically

useful. The reactivity of CF3CH(OH)O (10) should be much greater than THF

according to the kinetic data showing that 10 is 5 times more reactive than THF towards









hydrogen atom abstraction by the water soluble fluoroalkyl radical. With this goal in

mind, many addition experiments were attempted in which 10 was added with different

alkenes in different solvent systems. In addition, many initiation methods were attempted

including the method developed by Paleta (Scheme 3-4).

Na
0 Na-0 OH

F3 10 hv, acetone N CH2CH2CH2CH2COO
F3C OH
H20 _
H C2 +Na F3C


2

Scheme 3-4. Attempted alkene addition of 10

The results of many experiments are given in Table 3-5, and show that we were not

successful in propagating a chain process. The general procedure for all of these

reactions involves dissolving the alkoxide hydrate in the suitable solvent and adding the

appropriate alkene. 5 mol% of the initiator was added and the reaction mixture was

heated in cases where heating was required for initiation. 19F NMR was monitored for

indications that an addition had occurred, but from the results in Table 3-5, this was never

the case. It is hard to imagine that the labile hydrogen atom of CF3CH(OH)O was not

abstracted by one of these initiation methods, therefore, the probability is high that the

resulting radical does not add to any of the alkenes studied. One possibility for the

seemingly unreactive carbon centered radical is that it may too stable to add to any

alkene. It is not difficult to envision a "capto-dative" scenario in which the CF3 group

acts as the capto portion and the oxygen anion as the dative portion. Such stabilization of

radicals is well known to exist for similar electronic situations.







79


Table 3-5. Summary of attempted chain propagation reactions with 10
Alkene Initiation Acetonitrile a DMF a D20 a

AIBN x x

Bz202 x x

1-octene hv x x

hv, acetone x x

hv, Bz202 x x

AIBN x x

Bz202 x x

CN hv x x

hv, acetone x x

hv, Bz202 x x

AIBN x x

Bz202 x x

styrene hv x x

hv, acetone x x

hv, Bz202 x x

hv, acetone x

ACVAb x

\ hv, acetone x

o2c ACVA x

a. x indicates no reaction; b. 4,4'-azobis(4-cyanovaleric acid)







80


Another possibility to take advantage of the low BDEs of 0-trifluoromethyl

alkoxides was afforded by compound 11 (Scheme 3-5).


A

or hv
CF3

11



Scheme 3-5. Dissociation of compound 11



MgCI -78 C
+
F30 OEt diethyl ether


;F3
20% HC1 Ph
diethyl ether

kH
0


.CF3
NaH
diethyl ether


85%


O
S+ <

CF3


60%0 H2NN(Me)2
ethanol
cat. acetic acid


1. n-BuLi Ph CF3
Ph-------IIP
2. Mel
STHF N

80%


Scheme 3-6. Synthesis of compound 11

Compound 11 was synthesized as shown in Scheme 3-6, and was envisioned as a thermal

or photochemical free radical initiator for polymerizations. Compound 11 should be

susceptible to homolytic bond cleavage, as shown in Scheme 3-5, due to the stabilizing


96% OH









effect that the CF3 and O have on the formed radical. Known compound 11 was

synthesized by methods reported in recent literature. 110 Upon its synthesis, compound 11

was dissolved in DMF and subjected to UV light (254 nm). There was some evidence of

bond scrambling because 11 exists as a diasteriomeric mixture, (9:1) and photolysis

resulted in the ratio changing to 6:4 after only a few hours. Encouraged by these results,

styrene was added into the reaction cylinder but resulted in no observed polymerization.

From a pyrolysis point of view, 11 did not seem to undergo bond scrambling even though

it was subjected to temperatures of 180 C. After these discouraging results, 11 was no

longer studied as a possible free radical initiator.

3.3 Conclusions

The alkoxide functionality has long been known to provide acceleration to

sigmatropic processes where a bond to the carbon bearing the alkoxy group is broken.

Absolute rate data now demonstrate that an a-alkoxide also dramatically enhances

homolytic hydrogen atom abstractions by highly electrophilic perfluoro radicals.

Therefore, 0-fluorinated alkoxides exhibit bimolecular rate constants for H-abstraction by

a fluorinated radical in the 105 M-1 s-1 range, such rates representing enhancements

relative to their respective alcohols of between 100 and 1000-fold, depending on the

reactivity of the alkoxide. The monobasic sodium salts of chloral and floral hydrate

exhibit similar rate enhancements, relative to their respective hydrates. The extremely

large absolute rate constant associated with the monobasic sodium salt of fluoral hydrate

(171 x 103 M1 s-1) for H-atom abstraction led to an attempted alkene addition synthetic

application. However, there proved to be a problem associated in the attempted chain

process.









3.4 Experimental

All reagents used were commercially available, and were purchased from CIL,

Aldrich, Fisher, or SynQuest. All reagents were used without further purification, and all

anhydrous solvents were dried according to well known methods. NMR spectra and

kinetic 19F NMR measurements were performed at 282 MHz using a Varian VXR-300

spectrometer. All 1H NMR spectra were performed at 300 MHz on the same instrument.

All chemical shifts are reported downfield in ppm from the internal standards, CFC13 and

TMS, for fluorine and proton NMR, respectively.

3.4.1 Typical Procedure for Preparation of Alkoxide Sodium Salts

Hexafluoroisopropoxide, sodium salt (6):

NaH (0.534 g, 22 x 10-3 mol) was suspended in 30 mL of anhydrous diethyl ether under

nitrogen. The suspension was stirred and cooled to ice bath temperature.

Hexafluoroisopropanol (3.1 g, 31 x 10-3 mol) was added to 15 mL of anhydrous diethyl

ether and then added dropwise via an equalizing addition funnel to the NaH suspension.

The solution was allowed to stir for 3 hours during which time it reached room

temperature. The ether was removed by roto-evaporation and the resulting white solid

was dried via vacuum pump overnight to obtain hexafluoroisopropoxide, sodium salt

(2.66 g, 98.2% yield): 1H NMR (300 MHz, D20) 6 4.42 (hept, JHF = 6.9 Hz, 1H); 19F

NMR (282 MHz, D20) 6 -76.58 (d, JFH = 6.5 Hz, 6F).

Trifluoroethoxide, sodium salt (5):

White solid was obtained following the same general procedure (96% yield): 1H NMR

(300 MHz, D20) 6 3.93 (m, 2H); 19F NMR (282 MHz, D20) 6 -77.16 (m, 3F).

Trifluoroisopropoxide, sodium salt (7):




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HYDROGEN ATOM ABSTRACTION REACTIVITY OF A PRIMARY FLUOROALKYL RADICAL IN WATER By JOSEPH AARON CRADLEBAUGH A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2005

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This work is dedicated to my parents, Charles and Jo, who have always loved and supported me through the course of my life.

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iii ACKNOWLEDGMENTS Through the course of my graduate studies he re at the University of Florida I have been blessed with the opportunity to befrie nd some wonderful people. I can honestly say that graduate school has been some of the best years of my life, and I would like to express my appreciation to some special people who have aided in my education. My respect and gratitude go out to my gra duate research advisor, Dr. William R. Dolbier, Jr., for guiding me in my development as a researcher. I am especially grateful for his insightful discussions and encourag ement during my time at the University of Florida. I would also like to thank the members of my supervisory committee for their advice, and making time in their busy schedules to serve on my committee. They are Dr. Kenneth Wagener, Dr. Ronald Castel lano, Dr. Daniel Talham, and Dr. Anthony Brennan. I would also like to thank Dr. Ion Ghiviriga for helping me with NMR spectra interpretation, and inst rumental problems. It has been a pleasure working in the Do lbier research group, and the experience will never be forgotten. I w ould like to thank Dr. Li Zha ng, Dr. John Marshall Baker, Dr. Yian Zhai, and Dr. Bob Shelton, for their fr iendship and helpful discussions. I would especially like to thank Dr. Tyler Schertz and Dr. Chaya Pooput for their constant words of encouragement and support. Finally, I would like thank all of the Dolbier group members, both past and present.

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iv The North Central Soccer Officials Associa tion has been a major source of contact with people from many different fields and b ackgrounds. I have enjoyed officiating with all of the members, and wish them many fun-filled days on the pitch. Finally, I would like to expre ss my appreciation and love for my parents who have always supported me.

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v TABLE OF CONTENTS page ACKNOWLEDGMENTS..................................................................................................iii LIST OF TABLES...........................................................................................................viii LIST OF FIGURES...........................................................................................................xii LIST OF SCHEMES..........................................................................................................xv LIST OF EQUATIONS....................................................................................................xvi ABSTRACT....................................................................................................................xvii CHAPTER 1 GENERAL INTRODUCTION TO RADICAL CHEMISTRY.................................1 1.1 General Introduction............................................................................................1 1.2 Fluorine Substituent Effects.................................................................................2 1.3 Structure of Fluorinated Radicals.........................................................................3 1.4 Thermodynamic Properties of Fluorinated Radicals............................................4 1.5 Alkene Addition Reactions..................................................................................6 1.6 Hydrogen Atom Abstractions...............................................................................9 1.7 Fluorinated Free Radical Chemistry in Aqueous Solutions...............................13 2 ABSOLUTE RATE CONSTANTS FOR HYDROGEN ATOM ABSTRACTION REACTIONS BY A PRIMARY FL UOROALKYL RADICAL IN WATER.........16 2.1 Introduction........................................................................................................16 2.2 Results................................................................................................................19 2.2.1 LFP Determination of the Rate Constant for Addition of RfSO3 to 2 ..........................................................................................20 2.2.2 LFP Probe Experiments.........................................................................22 2.2.3 Competition Experiment to Determine kD for THF-d8..........................24 2.2.4 Obtaining Relative and Absolu te H-Atom Abstraction Rate Constants.............................................................................................26 2.3 Discussion of the Kinetic Data...........................................................................30 2.3.1 Rate Constants for H-Atom Ab stractions in Water by Primary Fluoroalkyl Radicals............................................................................31

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vi2.3.2 Comparison of Rate Constants fo r H-atom Abstraction by Primary Fluoroalkyl Radicals in Water and in BTB..........................................32 2.4 Conclusions........................................................................................................35 2.5 Experimental......................................................................................................35 2.5.1 Sodium 5-iodo-3-oxaocta fluoropentanesulfonate ( 1 )............................36 2.5.2 Sodium 4-( -methyl)vinylbenzoate ( 2 ).................................................36 2.5.3 Sodium 5-H-3-oxaoctafluoropentanesulfonate ( 3H)..............................38 2.5.4 Kinetic Measurements by Time-R esolved Laser Flash Photolysis.......38 2.5.5 Verification of Probe Addition Rate Constant.......................................39 2.5.6 Laser Flash Photolysis Probe Experiments............................................39 2.5.7 General Procedure for Ki netic Competition Studies.............................39 2.5.8 Tables of Kinetic Data and Plots...........................................................41 3 RATE CONSTANTS FOR OXYANI ON ACCELERATED HYDROGEN ABSTRACTION REACTIONS FROM ALKOXIDES BY A PERFLUOROALKYL RADICAL IN WATER......................................................68 3.1 Introduction........................................................................................................68 3.2 Results and Discussion.......................................................................................71 3.2.1 Kinetic Results.......................................................................................71 3.2.2 Possible Synthetic Applications............................................................77 3.3 Conclusions........................................................................................................81 3.4 Experimental......................................................................................................82 3.4.1 Typical Procedure for Preparat ion of Alkoxide Sodium Salts..............82 3.4.2 Preparation of 2-deuteriohexa fluoroisopropoxide, sodium salt ( 8 ).......83 3.4.3 Typical Procedure for the Preparat ion of Monobasic Sodium Salts of Hydrates...............................................................................................83 3.4.4 General Procedure for 19F NMR Kinetic Experiments..........................84 3.4.5 Kinetic Measurements by Time-R esolved Laser Flash Photolysis.......85 3.4.6 Preparation of Compound 11 .................................................................85 3.4.7 Tables of Kinetic Data and Plots...........................................................88 4 LARGE PRIMARY KINETIC ISOTOPE EF FECTS IN THE ABSTRACTION OF HYDROGEN FROM ORGANIC COMP OUNDS BY A FLUORINATED RADICAL IN WATER..........................................................................................102 4.1 Introduction......................................................................................................102 4.2 Results..............................................................................................................104 4.2.1 Secondary Deuteriu m Isotope Effects.................................................107 4.2.2 Primary Deuterium Isotope Effects.....................................................111 4.3 Discussion........................................................................................................112 4.4 Conclusion........................................................................................................116 4.5 Experimental....................................................................................................116 4.5.1 General Procedure for Co mpetition Kinetic Studies...........................117 4.5.2 Correction for the Diethyl Ether Impurity in CH3CHDOH.................117 4.5.3 Procedure for Measurement of th e Intramolecular Isotope Effects.....118

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vii4.5.4 Preparation of CH3CHDOH................................................................119 4.5.5 General Procedure for the Acetone Arrhenius Data............................119 4.5.6 Tables of Kinetic Data and Plots.........................................................121 APPENDIX SELECTED NMR SPECTRA..................................................................133 LIST OF REFERENCES.................................................................................................139 BIOGRAPHICAL SKETCH............................................................................................146

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viii LIST OF TABLES Table page 1-1. Hyperfine splitting constants.......................................................................................4 1-2. BDEs for various hydrocarbons..................................................................................5 1-3. BDEs for fluorinated methanes and ethanes................................................................5 1-4. Rho ( ) parameters of radical reactions.......................................................................6 1-5. Relative rates of radical addition to CF2=CF2/CH2=CH2............................................7 1-6. Relative rate of addition of CF3 to alkenes.................................................................7 1-7. Absolute rate constant s for alkene additions at 25 C in Freon 113............................8 1-8. Hydrogen atom abstractions by n -C7F15 and R-CH2 in C6D6 at 30 C.......................9 1-9. Absolute rate constant s for H-atom abstraction by n -C4F9 at 25 C.........................12 1-10. Absolute rate constants for RfSO3 addition in water and comparison to F113.....14 2-1. Pseudo 1st order rate constant for probe addition......................................................21 2-2. Determination of kH for THF via probe competition.................................................23 2-3. Rate data for THF/THF-d8 competition towards RfSO3Na Radical.........................28 2-4. Rate constants fo r H-atom abstractions.....................................................................29 2-5. Rate data for THF/THF-d8 competition.....................................................................41 2-6. Rate data for CH3OH/THF-d8 competition...............................................................42 2-7. Rate data for CH3CH2OH/THF-d8 competition.........................................................43 2-8. Rate data for (CH3)2CHOH/THF-d8 competition......................................................44 2-9. Rate data for ethylene glycol/THF-d8 competition....................................................45 2-10. Rate data for 2,3-butanediol/THF-d8 competition...................................................46

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ix 2-11. Rate data for me thyl glycolate/THF-d8 competition...............................................47 2-12. Rate data for CF3CH2OH/THF-d8 competition.......................................................48 2-13. Rate data for (CF3)2CHOH/CD3OD competition....................................................49 2-14. Rate data for CH3OCH2CH2OCH3/THF-d8 competition.........................................50 2-15. Rate data for (CH3)2CO/THF-d8 competition..........................................................51 2-16. Rate data for CH3COOH/THF-d8 competition........................................................52 2-17. Rate data for CH3COONa/THF-d8 competition......................................................53 2-18. Rate data for CH3CH2COOH/THF-d8 competition.................................................54 2-19. Rate data for CH3CH2COONa/THF-d8 competition...............................................55 2-20. Rate data for HSCH2CH2SO3Na/THF-d8 competition............................................56 2-21. Rate data for (HOCH2CH2CH2)3SiH/THF-d8 competition.....................................57 2-22. Rate data for Me3N+CH2SiMe2H Br-/THF-d8 competition.....................................58 2-23. Rate data for H3PO3/THF-d8 competition...............................................................59 2-24. Rate constants (kgl) for RfSO3 + 4-(1-propenyl)benzoate Na+, 2 in water..........60 2-25. LFP kinetic probe data yielding kH for THF...........................................................61 2-26. LFP kinetic probe data yielding kH for isopropanol................................................66 3-1. Correlation between rate constant and calculated -C-H BDEs...............................70 3-2. Rate constants for hydrogen abstrac tion from fluorinated and non-fluorinated alcohols.....................................................................................................................71 3-3. Absolute rate constants for alkoxides and corre sponding alcohols...........................72 3-4. Absolute rate constants of hydrates and monobasic hydrate anions.........................76 3-5. Summary of attempted chain propagation reactions with 10 ....................................79 3-6. Rate data for sodium hexafluoroisopropoxide/THF-d8 competition.........................88 3-7. Rate data for THF/sodium hexafluoroisopropoxide-D competition..........................89 3-8. Rate data for sodium trifluoroethoxide/THF-d8 competition....................................90

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x 3-9. Rate data for sodium hexafluoroi sopropoxide/sodium hexafluoroisopropoxide-D competition...............................................................................................................91 3-10. Rate data for sodium trifluoroe thoxide/sodium hexafluoroisopropoxide-D competition...............................................................................................................92 3-11. Rate data for sodium trifluoroisopropoxide/THF-d8 competition...........................93 3-12. Rate data for he xafluoroisopropanol/MeOD-d4 competition..................................94 3-13. Rate data for Cl3CCH(OH)2/THF-d8 competition...................................................95 3-14. Rate data for Cl3CCH(OH)ONa/THF-d8 competition.............................................96 3-15. Rate data for F3CCH(OH)2/THF-d8 competition.....................................................97 3-16. Rate data for F3CCH(OH)ONa/THF-d8 competition..............................................98 3-17. Rate data for H-atom abstracti on from sodium trifluoroethoxide by RfSO3Na in water.........................................................................................................................99 3-18. Rate data for H-atom abstracti on from sodium trifluoroisopropoxide by RfSO3Na in water...................................................................................................................101 4-1. Observed kinetic isotope e ffects for several organic compounds...........................107 4-2. Data used to calculate sec ondary deuterium isotope effects...................................109 4-3. Corrected primary isotope effects............................................................................112 4-4. Arrhenius data for acetone at 24 C.........................................................................121 4-5. Arrhenius data for acetone at 56 C.........................................................................122 4-6. Arrhenius data for acetone at 80 C.........................................................................123 4-7. Rate data for CH3OH/CD3OD competition.............................................................124 4-8. Rate data for THF/THF-d8 competition...................................................................125 4-9. Rate data for (CH3)2CHOH/(CD3)2CDOD competition..........................................126 4-10. Rate data for CH3CH2OH/CD3CD2OD competition.............................................127 4-11. Rate data for CH3CH2OH/CH3CD2OD competition.............................................128 4-12. Rate data for (CH3)2CO/(CD3)2CO competition...................................................129 4-13. Rate data for CH3COOH/CD3COOD competition................................................130

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xi 4-14. Rate data for hexafluoroisopropoxi de/hexafluoroisopropoxide-d competition.....131 4-15. Rate data for he xadeuteroisopropanol/THF-d8 competition..................................132

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xii LIST OF FIGURES Figure page 1-1. Fluorinated radical pyramidalization...........................................................................3 1-2. Polar transition state for alkene additions of perfluoroalkyl radicals..........................8 1-3. Polar transition states.................................................................................................10 2-1. Polar transition state for an H-atom abstraction........................................................17 2-2. Plot of Pseudo 1st order rates vs. concentration of 2 .................................................21 2-3. Plot of kexp vs. [THF].................................................................................................24 2-4. 19F NMR spectra of hydrogen and deuterium reduced products...............................25 2-5. Plot of [ 3H]/[ 3D] vs. [THF]/[THF-d8]........................................................................28 2-6. Charge separated polar transition state for addition to C=C double bonds...............33 2-7. Competing H-atom abstraction and -scission pathways..........................................34 2-8. Hydrogen bonding of an alcohol to a water molecule...............................................35 2-9. Plot of [ 3H]/[ 3D] vs. [THF]/[THF-d8]........................................................................41 2-10. Plot of [ 3H]/[ 3D] vs. [CH3OH]/[THF-d8].................................................................42 2-11. Plot of [ 3H]/[ 3D] vs.[CH3CH2OH]/[THF-d8]...........................................................43 2-12. Plot of [ 3H]/[ 3D] vs. [(CH3)2CHOH]/[THF-d8]........................................................44 2-13. Plot of [ 3H]/[ 3D] vs. [ethylene glycol]/[THF-d8].....................................................45 2-14. Plot of [ 3H]/[ 3D] vs. [2,3-butanediol]/[THF-d8].......................................................46 2-15. Plot of [ 3H]/[ 3D] vs. [methyl glycolate]/[THF-d8]...................................................47 2-16. Plot of [ 3H]/[ 3D] vs. [CF3CH2OH]/[THF-d8]...........................................................48 2-17. Plot of [ 3H]/[ 3D] vs. [(CF3)2CHOH]/[CD3OD]........................................................49

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xiii 2-18. Plot of [ 3H]/[ 3D] vs. [CH3OCH2CH2OCH3]/[THF-d8].............................................50 2-19. Plot of [ 3H]/[ 3D] vs. [(CH3)2CO]/[THF-d8].............................................................51 2-20. Plot of [ 3H]/[ 3D] vs. [CH3COOH]/[THF-d8]............................................................52 2-21. Plot of [ 3H]/[ 3D] vs. [CH3COONa]/[THF-d8]..........................................................53 2-22. Plot of [ 3H]/[ 3D] vs. [CH3CH2COOH]/[THF-d8].....................................................54 2-23. Plot of [ 3H]/[ 3D] vs. [CH3CH2COONa]/[THF-d8]...................................................55 2-24. Plot of [ 3H]/[ 3D] vs. [HSCH2CH2SO3Na]/[THF-d8]................................................56 2-25. Plot of [ 3H]/[ 3D] vs. [(HOCH2CH2CH2)3SiH]/[THF-d8].........................................57 2-26. Plot of [ 3H]/[ 3D] vs. [BrMe3NCH2SiMe2H]/[THF-d8].............................................58 2-27. Plot of [ 3H]/[ 3D] vs. [H3PO3]/[THF-d8]...................................................................59 3-1. Anionic oxy-Cope rearrangement rate enhancement................................................68 3-2. Isopropanol reactivities in BTB and water................................................................69 3-3. Photo-sensitized addition of alcohols and cyclic ethers............................................77 3-4. Plot of [ 3H]/[ 3D] vs. [sodium hexafluoroisopropoxide]/[THF-d8].............................88 3-5. Plot of [ 3H]/[ 3D] vs. [THF]/[sodium he xafluoroisopropoxide-D].............................89 3-6. Plot of [ 3H]/[ 3D] vs. [sodium trifluoroethoxide]/[THF-d8]........................................90 3-7. Plot of [ 3H]/[ 3D] vs. [sodium hexafluor oisopropoxide]/[sodium hexafluoroisopropoxide-D]......................................................................................91 3-8. Plot of [ 3H]/[ 3D] vs. [sodium trifluoroethoxide]/ [sodium hexafluoroisopropoxide-D]........................................................................92 3-9. Plot of [ 3H]/[ 3D] vs. [sodium trifluoroisopropoxide]/[THF-d8].................................93 3-10. Plot of [ 3H]/[ 3D] vs. [hexafluoroisopropanol]/[MeOH-d4]......................................94 3-11. Plot of [ 3H]/[ 3D] vs. [Cl3CCH(OH)2]/[THF-d8].......................................................95 3-12. Plot of [ 3H]/[ 3D] vs. [Cl3CCH(OH)ONa]/[THF-d8].................................................96 3-13. Plot of [ 3H]/[ 3D] vs. [F3CCH(OH)2]/[THF-d8]........................................................97 3-14. Plot of [ 3H]/[ 3D] vs. [F3CCH(OH)ONa]/[THF-d8]..................................................98

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xiv 4-1. Rate constants for H-abstractio n from isopropanol in BTB and water...................102 4-2. Typical competition experiment..............................................................................103 4-3. Competition between acet one and deuterated acetone............................................105 4-4. Plot of the kinetic data for acetone..........................................................................106 4-5. Transition state for D-abstractio n from pentadeuteroethanol showing and secondary deuteriums.............................................................................................108 4-6. Secondary deuterium isotope eff ects for a radical forming reaction.......................111 4-7. Temperature profile for acetone, ln(kH/kD) vs. 1/T.................................................115 4-8. Plot of Arrhenius data for acetone at 24 C.............................................................121 4-9. Plot of Arrhenius data for acetone at 56 C.............................................................122 4-10. Plot of Arrhenius data for acetone at 80 C...........................................................123 4-11. Plot of [ 3H]/[ 3D] vs. [CH3OH]/[CD3OD]...............................................................124 4-12. Plot of [ 3H]/[ 3D] vs. [THF]/[THF-d8]....................................................................125 4-13. Plot of [ 3H]/[ 3D] vs. [(CH3)2CHOH]/[(CD3)2CDOD]............................................126 4-14. Plot of [ 3H]/[ 3D] vs. [CH3CH2OH]/[CD3CD2OD].................................................127 4-15. Plot of [ 3H]/[ 3D] vs. [CH3CH2OH]/[CHCD2OD]..................................................128 4-16. Plot of [ 3H]/[ 3D] vs. [(CH3)2CO]/[(CD3)2CO].......................................................129 4-17. Plot of [ 3H]/[ 3D] vs. [CH3COOH]/[CD3COOD]....................................................130 4-18. Plot of [ 3H]/[ 3D] vs. [(CF3)2CHO]/[CF3)2CDO].................................................131 4-19. Plot of [ 3H]/[ 3D] vs. [(CD3)2CHOH]/[THF-d8]......................................................132

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xv LIST OF SCHEMES Scheme page 1-1. Photo initiated chain reaction....................................................................................11 2-1. Chain reaction involving a hydrogen atom abstraction.............................................16 2-2. Synthesis of compound 1 ...........................................................................................18 2-3. Radical generation and addition to sodium 4-(1-propenyl)benzoate.........................20 2-4. Synthesis of sodium 4-( -methyl)vinylbenzoate ( 2) .................................................22 2-5. Formation of hydrogen reduced product....................................................................24 2-6. Competition experiment............................................................................................27 2-7. Possible electron transfer mechanism........................................................................30 3-1. Competition scheme showing trifluoroethoxide ( 5 ) and THF-d8..............................72 3-2. Competition with no THF-d8.....................................................................................73 3-3. Preparation of the monobasic sodium salts...............................................................75 3-4. Attempted alkene addition of 10 ...............................................................................78 3-5. Dissociation of compound 11 ....................................................................................80 3-6. Synthesis of compound 11 .........................................................................................80

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xvi LIST OF EQUATIONS Equations page 2-1. Global rate c onstant calculation................................................................................21 2-2. Kinetic probe expression...........................................................................................22 2-3. Simplified kinetic probe expression..........................................................................23 2-4. Competition expression for THF/THF-d8..................................................................26 2-5. Competition methodology.........................................................................................26 3-1. Calculation of kH (HFIPO) without using THF-d8....................................................74 3-2. Calculation of kH (HFIPO) using a reverse competition........................................74 4-1. Calculation of isotope effects for t -BuMe2SiH and THF........................................104 4-2. Calculation of the -secondary deuterium isotope effect for CH3CHDOH............109 4-3. Calculation of the -secondary deuterium isotope effect for CHD2OH..................110

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xvii Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy HYDROGEN ATOM ABSTRACTION REACTIVITY OF A PRIMARY FLUOROALKYL RADICAL IN WATER By Joseph Aaron Cradlebaugh December 2005 Chair: William R. Dolbier, Jr. Major Department: Chemistry A combination of laser flash photolysis a nd competitive kinetic methods has been used to measure the absolute bimolecular rate constants for hydrogen atom abstraction in water from a variety of organic substrates including alcohols, ethers, carboxylic acids, fluorinated alkoxides, aldehyde hydrates, and the monobasic sodium salts of aldehyde hydrates by the perfluor oalkyl radical, CF2CF2OCF2CF2SO3 Na+. Comparison, where possible, of these rate consta nts with those previously meas ured for analogous reactions in the non-polar organic solven t, 1,3-bis(trifluoromethyl)ben zene show that the alcohols are 2-5 times more reactive in the water solvent and that the ethers react at the same rate in both solvents. A transition state for hydrogen abstraction th at is more reminiscent of an intimate ion pair than a solvent separate d state ion pair is i nvoked to explain these modest solvent effects. The bimolecular rate constants observed for the -fluorinated alkoxides were in the 105 M-1 s-1 range, such rates representing enhancem ents over their respective alcohols of

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xviii between 100 and almost 1000-fold, depending on the reactivity of the alkoxide. Likewise, the monobasic sodium salts of chlora l and floral hydrate exhibit similar rate enhancements, relative to their respective hyd rates. In addition, the largest bimolecular rate constant ever observed for hydrogen atom abstraction by this radical is determined for the monobasic sodium salt of fluoral hydrate. Kinetic isotope effects have also been de termined for the abstraction of hydrogen from a series of organic s ubstrates. Both primary and secondary deuterium isotope effects were measured, with the primary is otope effects ranging in value from 4.5 for isopropanol to 21.1 for acetic acid. The values for the and -secondary deuterium isotope effects were 1.06 and 1.035 respectiv ely. It was concluded that tunneling contributes significantly to th e production of the observed, la rge primary kinetic isotope effects in these C-H abstraction reactions.

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1 CHAPTER 1 GENERAL INTRODUCTION TO RADICAL CHEMISTRY 1.1 General Introduction Organic synthesis involving fr ee radicals as reactive intermediates has advanced immensely over the past century. 1-3 The beginning of radical chemistry can be traced back to work presented by Gomberg in 1900 on Triphenylmethyl: An Instance of Trivalent Carbon. 4 However, a true understanding of the mechanistic implications of radical chemistry had to wait until the 1930s when a review by Walters and Hey demonstrated that radical mechanisms we re viable for a number of known reactions. 5 Despite the early advances in radical chem istry, carbon-based free radical chemistry was not viewed as feasible for organic synthe sis, and thus, lay largely dormant for many years. This view is perhaps best exemp lified in Wallings 1985 pe rspective, radical chemistry remained essentially mysterious to synthetic chemists. 6 As the synthetic community toiled with an understanding of carbon-based free radical chemistry, important progress had al ready been made in the area of polymer chemistry. Flory established the practicability of utilizing carbon-ba sed free radical chain processes of olefins to yield co mmercially valuable polymers. 7, 8 Free radical polymerization is of paramount importance today both in indust rial and laboratory preparations of remarkable materials, such as TEFLON. 9, 10 Free radical chemistry made headway in synthesis in the mid 1980s. Hart successfully showed in the synthesis of pyrrolizidines that radical chemistry could provide easy access to families of natural products. 11 Stork demonstrated that radical reacti ons were capable of a high degree of

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2 regioand stereoselectivity. 12 This progress in synthetic ra dical chemistry has led to an explosion in the use of free radical intermediates in chemistry today. 13-16 Even with the plethora of advances in the field of radical chemistry, very few results have been reported studying fluorin ated radicals in aqueous media. The fluoropolymer industry is unique in this aspect with the ma in thrust of its production methods utilizing fluoroalkyl radicals in aqueous solution. However, no kinetic data on hydrogen atom abstraction by fluoroalkyl radi cals from organic donors have ever been published. The manufacture of industrial fluoropolymers typi cally requires the use of Htransfer agents to control molecular wei ght and molecular wei ght distributions under aqueous dispersion, suspension, or emulsion polymerization conditions. 17-19 Common chain transfer agents include chloro form, hydrocarbons, alcohols, and ethers. 20, 21 But the recipes for their use are entirely empirical a nd there have been no systematic, quantitative kinetic data on their reactivity toward model propagating fluorinated radicals in aqueous media to guide their use, or the design of improved chain transfer agents. 1.2 Fluorine Substituent Effects Most of the influence fluorine, as a substituent, exhibits on radical structure and reactivity is a direct result of the ex treme electronic nature of fluorine. 22 There are generally two types of substituent effects: steric effects and polar (electronic) effects. Polar effects can be divided further into inductive and conjugative (resonance) effects. Due to fluorines small size, steric effects in the transition states of fluorinated free radical reactions do not play an integral role in their reac tivity. As a consequence of fluorine being the most electronega tive atom, fluorine is a strong inductive electron withdrawing group in all cases. However, bound fluorine atoms have 3 lone pairs of electrons in sp3 orbitals which may act as a very good electron donor to other

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3 systems. In relation to fluorinated free radicals, fluorines lone pair participates in orbital overlap with the semi-occupied molecular orbi tal (SOMO) of the radical center. The key to understanding substituent effects is to separate the resonance effects from the inductive effects, which is impossible for a subs tituent such as fluorine. The interplay of these contrasting polar effects makes fo r a complicated electronic picture. 1.3 Structure of Fluorinated Radicals Unlike the complex situation surrounding electronic effects, fluorine substitution has definite ramifications on the structure of radicals. For instance, the methyl radical has been shown by ESR spectroscopy to exist in a planar conformation. 23 Conversely, the outcome of fluorine substitution on the radicals conformation is a tendency to become pyramidal (Figure 1-1). 23-25 Figure 1-1. Fluorinated radical pyramidalization As mentioned before, ESR spectroscopy is the best method for determining the geometry of a radical. Nonplanarity brings about more s character in the SOMO which contains an unpaired electron. In terms of ESR spectroscopy, the increased s character is manifested by a greater ESR a13C hyperfine (hfs) splitting cons tant. The methyl radical has an a13C value of 38 G, which indicates a planar geometry. Upon fluorine substitution of the radical, it is not surprising that the a13C values increase greatly, with the trifluoromethyl radical having a valu e of 272 G, which indicates an sp3 hybridization. (Table 1-1). 23 H F H F H F Planar Methyl Radical Tetra h edralTrifluoro m et h y l Radical

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4 Table 1-1. Hyperfine splitting constants HFS CH3 CH2F CHF2 CF3 a (13C) 38.5 54.8 148.8 272 The electronegativity of fluorine is the primary cause of the observed structural changes upon fluorine substitution. Bents rule states, Atomic p character concentrates in orbitals directed toward electronega tive substituents, which permits more electronegative atoms a great er share of bonding electrons. 26 In addition, the unpaired electron in the SOMO would be thermodynami cally more stable because the SOMO will take on more s character as the number of fl uorines is increased. Conjugative effects may also contribute to the observed pyramidali zation, but work has been done showing that fluorines predominant influence is due to its strong inductive withdrawing effect. 27 1.4 Thermodynamic Properties of Fluorinated Radicals The ability of fluorine substituents to st abilize alkyl radicals centers on the same interaction between inductive and resonance effects which determines their structure. Substituents which are electronegative and bear lone pairs of electrons are expected to destabilize the radical via their withdrawing ability, and stabilize by their donation to the extent that the single elec tron is delocalized. Bond dissoci ation energies (BDEs) have historically been used as a measure of radical stabili ty. C-H BDEs for various hydrocarbon radicals are given in Table 1-2 a nd show that there is a direct correlation between radical stability and increased substitution. 28, 29 The same type of stabilization is observed for carbocations (3 > 2 > 1 > CH3) and can be attributed to hyperconjugative effects. The C-H BDEs of fluorinated meth anes and ethanes are gi ven in Table 1-3, and show quite different stabilization e ffects than their hydrocarbon analogues.

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5 Table 1-2. BDEs for various hydrocarbons (CH3)3C-H (CH3)2CH-H CH3CH2-H CH3-H BDE, kcal/mol 96.4 98.6 101.1 104.8 From the data it can be determined that one or two -fluorines provides slight stabilization, albeit destabilization is observed for the tr ifluoromethyl case. 28, 29 Table 1-3. BDEs for fluorin ated methanes and ethanes BDE, kcal/mol CH3-H 104.8 CH2F-H 101.2 CHF2-H 103.2 CF3-H 106.7 CH3CH2-H 101.1 CF3CH2-H 106.7 CH3CF2-H 99.5 CF3CF2-H 102.7 Although the experimental data for the etha ne series are limited, it does appear that -fluorine substitution results in radical de stabilization. It has been suggested by computational efforts that the inductive eff ect of a single fluorine atom adequately destabilizes an ethyl radical. 30

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6 1.5 Alkene Addition Reactions To obtain an understanding of fluoroalkyl radical reactivit y, the philicity of such radicals must be ascertained. Free radicals are classified as ei ther nucleophilic or electrophilic depending on their reactivity char acteristics in situations of differing electronic demand. Various Hammett studies have been performed to determine the electrophilicity or nu cleophilicity of radicals, wh ich are reflected by the rho ( ) parameters. Table 1-4 lists rho ( ) parameters for additions to substituted styrenes and the H-atom abstractions of radicals from substituted toluenes. Table 1-4. Rho ( ) parameters of radical reactions H-Atom Abstraction fromTo luene Addition to Styrene Radical a + + CH3 -0.1 -0.12 (CH3)C 0.49 1.1 c-C6H11 0.68 n-C6H13 0.45 n-C11H23 0.45 (CH3)3CO -0.32 -0.36 -0.27 -0.31 CCl3 -1.46 -1.46 -0.42 -0.43 n-C8F17 -0.53 a. references 31-41 From the parameters it is obvious that hydroca rbon radicals have nuc leophilic character and the halogenated and oxygen-centered radi cals have electrophilic character. 31-33, 42 The importance of philicity is also observed in the relative rate of addition of increasingly electrophilic radicals to ethyl ene and tetrafluoroethylene. Table 1-5 illustrates that

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7 increasing the electrophilicity of radicals lead s to slower addition rates to the electron poor alkene. 43-45 Table 1-5. Relative rates of radical addition to CF2=CF2/CH2=CH2 Radical kCF2=CF2 / kCH2=CH2 CH3 9.5 CH2F 3.4 CHF2 1.1 CF3 0.1 Szwarc also demonstrated how the electrophilicity of CF3 affects overall addition rates to various alkenes. As shown in Table 1-6, the rate of radical addition increases for the more electron rich alkenes. 46 Table 1-6. Relative ra te of addition of CF3 to alkenes Alkene krel 3.7 1.4 1 F F F F 0.15 Having established the fact that electrophilic fluorinate d radicals add to electron rich olefins at an accelerated rate over electron poor olef ins, it becomes necessary to compare the rates of addition of fluorinated radicals and their hydrocarbon analogues. One would predict the r eactivity of fluoroalkyl radicals to differ significantly from their hydrocarbon counterparts. The la tter are planar, electron rich -radicals, whereas

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8 fluoroalkyl radicals have been s hown to be pyramidal, electron poor -radicals. Absolute rate data for the addition of perfluoroalkyl radicals to va rious alkenes in solution have been obtained by laser flash photolysis (LFP). 47, 48 Table 1-7 shows the absolute rate constants, kadd, for perfluoroalkyl radi cal additions to severa l alkenes in Freon 113. Table 1-7. Absolute rate consta nts for alkene additions at 25 C in Freon 113 kadd(106M-1 s-1) Alkenes n -C3F7 n -C7F15 C2F5 CF3 RCH2 -methylstyrene 78 89 94 87 a 0.059 b -methylstyrene 3.8 3.7 7 17 c styrene 43 46 79 c 53 a 0.12 d pentafluorostyrene 13 23 c 26 a 0.31 a 1-hexene 6.2 7.9 16 2 x 10-4 e 1,4-dimethylenecyclohexane41 1 x 10-4 e a. Reference 49; b. Reference 50; c. Reference 51; d. Reference 52; e. Reference 53 It is apparent that fluoroalkyl radicals exhibit much more reactivity than their hydrocarbon analogues, with n -C3F7 adding 30,000 times faster to 1-hexene and 1,300 times faster to -methylstyrene than the alkyl radical. The high electrophilicities of perfluoroalkyl radicals appears to be the dominant factor which gives rise to th eir great reactivities in relation to their alkyl counterparts. 48 Figure 1-2. Polar transition state for alkene additions of perfluoroalkyl radicals R H H H CF3CF2CF2

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9 Polarization of the type shown in Figure 1-2 will stabilize th e charge separated transition state in which only a small amount of radica l character is conveyed to the alkene. 1.6 Hydrogen Atom Abstractions The rates of hydrogen atom abstractions by radicals are governed by the same factors which influence the rates of alkene additions. 54 Polar effects and thermodynamic considerations are extremely important in understanding rates of hydrogen abstraction. As might be expected, the BDE of the co mpound in which the hydrogen atom is being abstracted plays an apparent role. Table 1-8 gives absolute rate constants for the hydrogen atom abstraction reactions for both an n -alkyl and perfluor oalkyl radical (Rf) from electropositive donor atoms with benzenethiol (electronegative) being the exception, and correlates the BDE of the donors to the observed absolute rate constants. 55-57 All rate constants were determin ed via a combination of LFP and competition techniques. The BDEs simply reflect that the lower the bond dissociation energy for the electropositive donors, the faster the hydrogen atom abstraction for the two radicals since in all cases the new bond being formed is C-H. Table 1-8. Hydrogen atom abstractions by n -C7F15 and R-CH2 in C6D6 at 30 C kH / 106 M-1 s-1 Radical Et3SiH (TMS)2SiMeH(TMS)3SiH n -Bu3SnH PhSH n -C7F15 0.75 16.3 51 203 0.28 R-CH2 0.0007 0.037 0.46 2.7 150 BDE, kcal/mol 90.1 a 85.3 a 79.0 a 73.6 b a. Reference 58; b. Reference 59 In comparing the reactivity of the two primary radicals, n -C7F15 abstracts hydrogen from n -Bu3Sn-H ~75 times greater than the n -alkyl radical in deut erated benzene at 30 C.

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10 (TMS)3SiH showed an increased reactivity for n -C7F15 over R-CH2 of ~111 times, and (TMS)2SiMeH was ~441 times greater for th e perfluoroalkyl radical. The Et3SiH proved to be the poorest hydrogen donor of the electropositive donors, but showed the largest difference in reactivity of ~1000 times. For all the electropositiv e hydrogen donors, clearly th e rates of hydrogen atom abstractions are significantly greater with th e fluoroalkyl radical. McMillen and Golden have calculated that the BDE of Rf-H is approximately 9 kcal/mol greater than R-H. 60 Therefore, the increased exothermicity of hydr ogen atom abstractions to perfluoroalkyl radicals is likely the main cause of their gr eater reactivity over the alkyl counterparts. Another possible factor cont rolling the reactivity of hydrogen atom abstractions is evident in close examination of the rate data associated with benzenet hiol. In fact PhSH is the only instance given in which the rate of hydrogen atom abst raction is actually larger for the alkyl radical. The reason that the alkyl ra dical abstracts hydrogen atoms 536 times faster than the perfluoroalkyl radi cal is apparent when polar factors in the transition states are examined. Figure 1-3 shows that for electropositive atoms such as silanes and stannanes, a favorab le polarity is achieved in the transition state when they are reacted with electro philic perfluoroalkyl (Rf) radicals. Figure 1-3. Polar transition states However, benzenethiol is an electronegativ e hydrogen atom donor and prefers to react with nucleophilic al kyl radicals. RfH MR3 R H SPh Perfluoroalkyl radical preferred Alkyl radical preferred

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11 Until this point all hydrogen atom abstrac tions mentioned have involved the use of metal hydride donors, or benzenethiol. Due to their extreme electrophilicity, perfluoroalkyl radicals are able to rapidl y abstract hydrogen atoms from some organic compounds, whereas alkyl radicals can not sufficiently abstract hydrogen atoms to continue chain processes for synthetically usef ul reactions. Paleta has shown that clean chain processes occur between fluorinated alkenes and alcohols upon irradiation (Scheme 1-1). 61, 62 Scheme 1-1. Photo initiated chain reaction The absolute rate constants for hydrogen at om abstraction for highly electropositive atoms were in the 106 108 M-1 s-1 range. Due to carbon not be ing as electropositive and the fact that the BDE of C-H bonds are grea ter than that of me tal hydrides, hydrogen atom abstraction from organic compounds is much slower. Prior to the work presented in this dissertation, the only absolute rate cons tants for hydrogen atom abstractions were for perfluoroalkyl radicals in 1,3bis(trifluoromethyl)benzene (1,3 -BTB). The absolute rate constants were obtained through a bimolecular competition using t -BuSiMe2D as a deuterium donor, and a wi de range of organic co mpounds as hydrogen donors. 63 t -BuSiMe2D has a known rate of deuterium abstrac tion by perfluoroalkyl radicals in 1,3BTB (kD = 1.49 x 105 M-1 s-1). 64 Absolute rate constants fo r hydrogen atom abstractions by n -C4F9 in 1,3-BTB at 25 C are given in Table 1-9. 63,64 1,2-dichloroethane had the (CH3)2CHOH + CF2=CFOC2F5 (CH3)2C-CF2CFOC2F5Major productOH H h

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12 slowest rate, whereas tetrahydrothiophen had the fastest rate, which represented a 1000 fold difference in reactivity. Table 1-9. Absolute rate consta nts for H-atom abstraction by n -C4F9 at 25 C Hydrogen Donor kH / 102 M-1 s-1 Hydrogen Donor kH / 102 M-1 s-1 ClCH2CH2Cl 0.6 1,3,5-trioxane 9.7 C6H13Cl 21 1,4-dioxane 31 n -heptane 76 THP 70 cyclohexane 93 CH3OCH2OCH3 19 cyclopentane 104 (CH3OCH2)2 67 CH3OH 9.2 diethyl ether 220 (CH3)2CHOH 163 1,3-dioxolane 140 (CH3CHOH)2 50 THF 310 CH3OCH3 28 tetrahydrothiophene 355 The results listed in Table 1-9 illustrate the importance of steric, thermodynamic, and especially polar effects. For instance, even though an -chlorine is thermodynamically stabilizing, the observed C-H abstraction rate is severely hampered. 1-chlorohexane has been shown to have an overall per hydrogen reactivity which is considerably less than that of n -heptane. 64 Data have been presented that i ndicates that the per hydrogen rate constant for C-H abstracti on from a methyl group of n -heptane is 2.4 times larger than that of the CH2Cl carbon of 1-chlorohexane. 64 Moreover, none of the methyl groups of 1-chlorohexane are as reactive as n -heptanes. Clearly, the el ectron-withdrawing chlorine atom is destabilizing the normal transition st ate polarity associated with hydrogen atom abstraction.

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13 1.7 Fluorinated Free Radical Chemistry in Aqueous Solutions The use of water as a solvent for organi c reactions has been a subject of much review since the 1990s. 65-67 SN1 solvolysis reactions have been shown to be accelerated in aqueous solutions due to strong interacti ons between carbenium ions and water in the transitions state. Also, the use of water as a solvent is believed to be much better than organic solvents with respect to the environment. Literature pertaining to radical chemistr y conducted in water has been practically non-existent thus far. In th e early 1990s, water soluble tin reagents were synthesized for use in aqueous phase radical reactions. 68, 69 Most of the literature involving free radicals in water were viewed from a green ch emistry point of view, until 2000 when the Fujimoto group reported that trie thylborane induced atom transf er radical cyclization was found to proceed much better in wa ter than other organic solvents. 70 As previously mentioned, polymer chemistry has utilized aqueous phase radical chemistry for many years. 71, 72 Many different types of high weight polymers can be synthesized by aqueous phase radical chemistry. The temperature can easily be controlled for these reactions due to the ability of water to tran sfer heat readily. In addition, water has distinct advantages of being neither flammable nor toxic. The Dolbier group published kinetic data for addition to various substituted styrenes by a primary fluorin ated radical in water. 73 A water soluble fluoroalkyl radical (NaO3SCF2CF2OCF2CF2 or RfSO3 ) was generated by LFP and was observed, via UV spectroscopy, adding to water so luble styrenes. As was th e case for alkene addition reactions in organic solven ts, thermodynamic and polar effects were observed to be important factors in understanding the r eactivity. It was al so determined upon comparison of relative rate constants for the sa me series of styrenes in F113, that steric

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14 and thermodynamic factors were independent of the solvent. In addition, rate constants for the series in water were 5-9 times faster than was observed for the same series in F113 (Table 1-10). 73 Table 1-10. Absolute rate constants for RfSO3 addition in water and comparison to F113 Styrene kadd / 107 M-1 s-1 k(H2O) / k(F113) Ph-(p-CO2Na) 23.2 5.4 Ph-(p-CO2Na) 55.3 7.1 Ph-(p-CO2Na) 3.31 8.7 Ph NaO2C 1.88 5.0 Ph-(p-CH2CO2Na) 20.2 4.7 The reasoning given for the rate enhancements in water derived from the more effective stabilization of the polar transition state by the polar solvent, water, over the nonpolar organic solvent, F113 (see figure 1-2). Will the increased polarity of water accelerate hydrogen atom abstractions also? Due to the high value of fluoropolymers, the fluoropolymer industry has by far made the most progress in fluorinated free ra dical chemistry in water. Perfluoroalkenes can only be converted to high molecular weig ht polymers by free ra dical conditions. The polymerization of tetrafluoroe thylene (TFE) is carried out in aqueous media by a couple of different methods to yield polytetrafl uoroethylene (PTFE). Most fluoropolymers are made by aqueous dispersion, suspension, or emulsion techniques, and even though these techniques have stood the test of time, there are stil l problems to be so lved in the field.

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15 Perhaps the most evident problem in fluoropol ymer production is the early termination of chain processes due to hydrogen atom abstra ction by the propagating fluoro-radical. Early termination results in low molecular we ights for the polymer. The manufacture of industrial fluoropolymers typically requires th e use of H-transfer agents to control molecular weight and molecular weight distributions under aqueous dispersion, suspension, or emulsion pol ymerization conditions. 17, 18, 19 Common chain transfer agents include chloroform, hydrocarbons, alcohols, and ethers. 20,21 But the recipes for their use are entirely empirical and there have been no systematic, quantitative kinetic data on their reactivity toward model propaga ting fluorinated radicals in aqueous media to guide their use, or the design of improved chain transfer agents. Therefore, an understanding of structurereactivity relationships and the influence of reaction medium on the kinetics of C-H abst raction by perfluoroalkyl radicals has both scientific and practical re levance. With these fact ors in mind, the hydrogen atom abstraction reactivity of a prim ary fluoroalkyl radical in water will be studied to provide insight on whether solvent polarity and stru ctural changes to various hydrogen atom donors can indeed effect the rates of hydrogen atom abstractions. No kinetic data on hydrogen atom abstraction by fluor oalkyl radicals in water from organic donors have ever been published. The work presented here pr ovides the first set of such data.

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16 CHAPTER 2 ABSOLUTE RATE CONSTANTS FOR HYDROGEN ATOM ABSTRACTION REACTIONS BY A PRIMARY FL UOROALKYL RADICAL IN WATER 2.1 Introduction Perfluoroalkyl radicals exhi bit unusual reactivity char acteristics which derive largely from their great electr ophilicity but also, in part, from their pyramidal geometry at the radical center and the ther modynamics of their reactions. 74, 75 Thus, rate constants for hydrogen atom abstraction by perfluoroalkyl radicals from relatively electropositive atoms such as Sn, Si, and even from carbon ar e much larger than t hose of the analogous alkyl radicals. For example, the rate constants for hydroge n abstraction from n -Bu3SnH and Et3SiH by a primary perfl uoroalkyl radical ( n -Rf) are 85 and 1000 times larger, respectively, than by n -R. 55-57 Although the C-H bonds of simple functiona lized or non-functi onalized aliphatic organic compounds are effec tively inert towards abstra ction by alkyl radicals, perfluoroalkyl radicals are sufficiently reac tive that they can efficiently propagate synthetically useful free radi cal chain reactions, such as the one given in Scheme 2-1. 61 Scheme 2-1. Chain reaction invol ving a hydrogen atom abstraction O O F2C CFCF3 h (94%)CF2CHFCF3

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17 Similarly, and as discussed by Shtarev et al .,63 rate constants for the reactions of the n -octyl radical with THF and diethyl ether at 22 C (4.9 x 102 and 1.2 x 102 M-1 s-1, respectively) 76, 77 are considerably lower than those for the n -C4F9, 3.1 x 104 and 2.2 x 104 M-1 s-1, respectively, in 1,3-bis(trifluor omethyl)benzene (BTB). These and many other rate constants were obtained vi a competition experiments in which the relative rates of H-atom abst raction from the substrates were determined versus deuterium abstraction from t -BuSiMe2D (for which kD = 1.49 x 105 M-1 s-1). 63 Their work indicated that the rate cons tants for H-atom abstraction by the n -C4F9 radical depended on at least thre e factors: (i) the C-H bond dissocia tion enthalpy (BDE) (ii) steric effects and (iii) tran sition state polar effects. With regard to the last factor, it is worth noting that chloroalkane s are less reactive towards n -C4F9 than alkanes despite the fact that a chlorine atom lowers the C-H BD E at the carbon bearing the chlorine relative to the C-H BDE of the corresponding alkane. The electron-withdraw ing chlorine atom clearly destabilizes the normal polarized transition state for C-H abstraction by the electronegative n -C4F9 radical (Figure 2-1). Figure 2-1. Polar transition stat e for an H-atom abstraction Due to high electrophi licities and the ac knowledged importance of transition state polar effects on the reactivities of perfluoron -alkyl radicals in both hydrogen abstractions and alkene additions,74,75 the rates of such reactions might be expected to be strongly influenced by solvent polarity. 78 The only mention in literature pertaining to this C H CF2CF2CF3

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18 matter appeared in a footnote in an earlier publicati on reporting that CF3 and n -C3F7 add to styrene ~3 times and to pentafluorostyrene ~1.5 times more rapidl y in acetonitrile than in 1,1,2-trichloro-1,2,2-trifluoroethane (F113). 49 A broad investigation of absolute rate constants for alkene addition r eactions of fluorinated alkyl ra dicals in water has recently been published. 73 Since the rate constants for alkene additions and hydrogen abstractions in non-polar solvents (F113, C6D6, and BTB) are known,63,75 it should be possible to assess the significance of solvent effects on these reactions. To study perfluoroalkyl radicals in water, a water soluble radical s ource must be acquired. The perfluoroalkyl iodide radical precursors used in no n-polar solvents are not soluble in water. Sodium 5-iodo-3-oxaoctafluor opentanesulfonate 1 (ICF2CF2OCF2CF2SO3Na) proved to be a good water soluble model for the perfl uoroalkyl iodides. Known compound 1 can be easily prepared via hydrolysis of ICF2CF2OCF2CF2SO2F (Scheme 2-2). 73 ICF2CF2OCF2CF2SO2F 2NaOH H2O, 90 C 12 hrs, 90% ICF2CF2OCF2CF2SO3N a 1 Scheme 2-2. Synthesis of compound 1 Elemental analysis indicated that the isolated product is ICF2CF2OCF2CF2SO3NaH2O. Compound 1 will be abbreviated as IRfSO3 from this point forward. IRfSO3 shows a broad absorption ( max = 262 nm) in the UV/Vis. spectrum, which allows for photoinitiation to yield the reactiv e radical intermediate. In th e initial study, absolute rate constants for the addition of the RfSO3 to a series of water soluble alkenes bearing carboxylate ion functionality in aqueous so lution were measured via laser flash photolysis (LFP). 73 As was the case for the related st udies in F113 it was concluded that thermodynamic, polar, and steric effects probably all played some role in the dynamics of

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19 these additions. In particular, rate cons tants in water, althoug h nearing the diffusion limit, were all larger than those reported ear lier for their structural counterparts in F113, with rate enhancements of 3-9 fold. 48 It was concluded that these enhancements in water vs. F113 most probably arose from a more e ffective stabilization of the polar transition state for addition in the more polar solvent. Important for the work presented here in relation to hydrogen atom abstractions, one of the alkenes examined in the earlie r LFP study (sodium 4-(1-propenyl)benzoate) was used as a kinetic probe in further LFP e xperiments to obtain absolute rate constants for H-atom abstraction by th e fluoroalkyl radical (RfSO3 ) from THF and isopropanol in water. 73 2.2 Results To obtain absolute rate constants for hydrogen atom abstraction from organic substrates by the RfSO3 radical in water, it is necessary to determine at least one such rate constant directly. However, there is no known method to direc tly measure the rates of these fast, highly exothermic H-atom ab stractions. Consequently, an indirect competition method was necessary to determine absolute rate constants in water for Hatom abstraction by RfSO3 from a diverse range of substrat es. The course of action was to use an LFP probe experiment in conjunc tion with relative ra te constants obtained from competition experiments to derive absolu te rate constants for H-atom abstraction. The following scheme was devised: A. Determine the global rate constant of the primary fluor oalkyl radical, RfSO3 with sodium 4-( -methyl)vinylbenzoate (CH3CH=CHC6H4CO2Na, 2 ) in water by LFP. B. Use 2 as a kinetic probe to determine th e rate constants for H-abstraction by RfSO3 from THF and isopropanol.

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20 C. Determine the rate constant fo r deuterium abstraction from THF-d8 by RfSO3 via a direct competition between H-atom abst raction from THF and deuterium atom abstraction from THF-d8. D. Determine the relative rate constants for H-atom abstraction from a series of organic substrates vs. D-atom abstraction from THF-d8 via competition experiments and then convert these to absolu te rate constants. 2.2.1 LFP Determination of the Rate Constant for Addition of R f SO 3 to 2 RfSO3 radical is generated instantaneously by 308 nm LFP of the parent iodide in water at ambient temperature (Scheme 2-3). N a O3SCF2CF2OCF2CF2I NaO3SRfI h v H2O Na O3SCF2CF2OCF2CF2 NaO2C NaO2C RfSO3Na kexpmax = 320 nm 2 Be n z y lr a d ic a l Scheme 2-3. Radical generation and a ddition to sodium 4-(1-propenyl)benzoate In the presence of 2 the radical adds to the double bond leading to a benzyl radical transient which can be detected at 320 nm in the UV/Visible spectrum. The grow in of the benzyl radical follows pseudo-first-order-k inetics and the global ra te constant can be calculated from the experimental growth curves measured over a range of concentrations of 2 (Equation 2-1).

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21 k(exp) vs 2y = 3.841E+07x + 1.459E+04 R2 = 9.880E-01 0 50000 100000 150000 200000 250000 300000 00.0010.0020.0030.0040.0050.0060.007 [2]k(exp) Equation 2-1. Global rate constant calculation As discussed previously,48 the global reactions of RfSO3 with an alkene such as 2 are comprised almost entirely of addition, with less than 5% being due to H-abstraction, i.e. kgl kadd. An example of the kinetic data obtaine d for these additions is shown in Table 2-1, and Figure 2-2. Table 2-1. Pseudo 1st order rate constant for probe addition 2 / M kexp / s-1 5.89 x 10-3 2.38 x 105 4.16 x 10-3 1.81 x 105 3.21 x 10-3 1.32 x 105 2.21 x 10-3 1.08 x 105 1.68 x 10-3 7.27 x 104 Figure 2-2. Plot of Pseudo 1st order rates vs. concentration of 2 kexp(320nm)=ko+kgl[ 2 ]

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22 The slope of the plot of kexp values vs. [ 2 ] yields the second order rate constant, kadd = 3.9 x 107 M-1 s-1, as an average for two trials. Known compound 2 was prepared in three steps from p-bromobenzaldehyde (Scheme 2-4). 80 Br CH=CHCH3 Br CH=CHCH3 NaOOC CH=CHCH3 HOOC O H CH3CH2PPh3Br, n -BuLi THF, 92% 1. t -BuLi, THF, -78 C 2. CO2, H+, 95% NaOH, MeOH 72% 2 Scheme 2-4. Synthesis of sodium 4-( -methyl)vinylbenzoate ( 2) The first step involves a Wittig reaction to give p-bromo-methylstyrene, followed by a lithium halogen exchange with t -BuLi and carbonation with CO2. The Sodium salt is obtained upon treatment with NaOH until neutral pH is obtained. 2.2.2 LFP Probe Experiments Although the alkyl radicals derived by H-atom abstraction from THF and isopropanol have insufficient extinction coefficients to be monitored by UV/Vis. spectroscopy, the rate cons tants for the reactions of these H-donors with RfSO3 can be obtained by using 2 as a kinetic probe (equation 2-2). 79 Equation 2-2. Kinetic probe expression kex p (320nm)=ko+k g l [ 2 ]+kH[H-Donor]

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23 The experimental pseudo-first-order rate constant is now the sum of the rate constants for addition to 2 and H-atom abstraction from the H-donor. At constant [ 2 ] Equation 2-2 can be simplified and Equation 2-3 is obtained. Equation 2-3. Simplified kinetic probe expression Plots of kexp vs. [H-Donor] yield stra ight line fits with R2 greater than 0.96 in all cases. The second order rate constants, kH, for H-atom abstraction ar e readily obtained from the slopes of these lines. For THF and isopropanol, kH = 3.3 x 104 and 4.0 x 104 M-1 s-1, respectively, for an average of three or more experiments each. An example of the kinetic data obtained for the ki netic probe experiments is gi ven in Table 2-2 and Figure 2-3 for THF. Both THF and isopropanol were chosen for these kinetic probe experiments because they have similar rate constants to that of probe 2 Table 2-2. Determination of kH for THF via probe competition [THF] / M kexp / s-1 [ 2 ] / M 0.00 7.04 x 104 1.70 x 10-3 0.129 7.35 x 104 1.70 x 10-3 0.194 7.96 x 104 1.70 x 10-3 0.290 7.99 x 104 1.70 x 10-3 0.436 8.39 x 104 1.70 x 10-3 0.653 8.96 x 104 1.70 x 10-3 0.980 1.04 x 105 1.70 x 10-3 1.470 1.18 x 105 1.70 x 10-3 k exp(320 n m )= k o+ k H[ H -Do n or]

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24 Rate of hydogen abstraction from THFy = 32438x + 70527 R2 = 0.9906 0 20000 40000 60000 80000 100000 120000 140000 00.20.40.60.811.21.41.6 [THF]k(exp) Figure 2-3. Plot of kexp vs. [THF] 2.2.3 Competition Experiment to Determine k D for THF-d 8 The reaction of the perfluoroiodide with THF using UV initiation proceeds via a clean, rapid free radical chain pr ocess to give reduced product, 3H, in essentially quantitative yield (Scheme 2-5). Scheme 2-5. Formation of hydrogen reduced product Compound 3H has been characterized and is include d in the experimental section. The ratio of the rate constant for H-atom abstra ction from THF to D-atom abstraction from THF-d8, was determined by using various mixtures of THF and THF-d8 and measuring [NaO3SRfH]/[ NaO3SRfD] ratios. As reported earlier, the 19F NMR signals for NaO3SCF2CF2OCF2CF2I NaO3SCF2CF2OCF2CF2H h R T THF, H2O 3H (NaO3SRfH) quant.

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25 HCF2CF2OCF2CF2SO3 ( 3H) and DCF2CF2OCF2CF2SO3 ( 3D) are well separated and a simple integration of the signals provides the relative concentr ations of these two products (Figure 2-4). 63 Figure 2-4. 19F NMR spectra of hydrogen and deuterium reduced products The hydrogen reduced product appears as a doub let of triplets at -138.3 ppm, and the deuterium reduced product shows up as a multiplet at -139.0 ppm in the 19F NMR. A plot of the [ 3H]/[ 3D] ratios vs. the [THF]/[THF-d8] ratios gives a straight line (Equation 2-4), the slope of which is the kinetic isotope effect, kH/kD = 7.9 0.4 and

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26 since the value of kH is known kD can be calculated. Hence, kD = 3.3 x 104 / 7.9 = 4.2 x 103 M-1 s-1. Equation 2-4. Competition expression for THF/THF-d8 With the rate constant for kD(THFd8) in hand, it now becomes possible to calculate the absolute rate constants for a number of organic H-atom donors. 2.2.4 Obtaining Relative and Absolute H-Atom Abstraction Rate Constants Competition experiments using THF-d8 and an H-donor permitted fast, clean, high yield reactions with virtually all of the organic substrates studied. Many other D-donors were investigated for use in competition experiments, but THF-d8 appears to be superior for our competition experiments. As brie fly mentioned in the previous section, by varying the starting concentr ation of the H-donor a plot of the product ratio (from 19F NMR) versus the ratio of reactant concen trations yields a linear correlation. The competition methodology expression is gi ven for all cases in Equation 2-5. Equation 2-5. Competition methodology The only reason a bimolecular process, as is th e case here, can be expressed with such an equation is that the concentration of hydroge n and deuterium donors ar e in great excess to the radical precursor (at least 15 times for a ll cases). Although pseudo first order kinetic requirements have been met, rate constants for the bimolecular processes are given as second order. Scheme 2-6 gives an accura te picture of the competition experiments. ] d [THF k [THF] k ] [ ] [8 D HD H3 3 Donor] H ][ [ ] d THF ][ [ k k thus, ] d [THF k Donor] [H k ] [ ] [8 D H 8 D H D H D H3 3 3 3

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27 Scheme 2-6. Competition experiment The competition experiments are usually performed using quartz NMR tubes as the reaction vessels. Six samples with varied [H-Donor] concentrations and constant THF-d8 concentrations are added to the NMR tubes al ong with water and the radical precursor. The total volume inside each NMR tube is kept constant through all experiments (565 L). To each NMR tube a capillary containing C6D6 as the lock solvent and CFCl3 as the standard are added. The NMR tubes are degassed via three free-pump-thaw cycles, and allowed to return to room temperat ure. The samples are then placed in a photochemical UV reactor (254 nm) for 12 hours. Upon obtaining 19F NMR spectra for each sample and careful integration of the pr oduct peaks, it is possible to obtain the relative rate constants, kH / kD(THF-d8). Table 2-3 lists a sample of relative rate data. The relative rate constants, kH/kD, are obtained by plotting the ratio of substrate concentrations versus product ra tios. A typical plot of [ 3H]/[ 3D] vs. [H-Donor]/[THF-d8] is shown for THF in Figure 2-5. Values of kH/kD(THFd8) and the values of kH derived from the known value of kD(THFd8) are collected in Table 2-4. O3SRfI Radical Precursor h H2O O3SRf H-Donor kHkDTHF-d8O3SRfH O3SRfD exclusively f r o m H-Dono r exclusively from THF-d81 3H3D

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28 Table 2-3. Rate data for THF/THF-d8 competition towards RfSO3Na Radical [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [THF]/ [THF-d8] [ 3H]/[ 3D] a 0.013 1.29 0.204 1.67 0.013 1.28 0.415 3.47 0.013 1.28 0.605 5.03 0.013 1.28 0.809 6.68 0.013 1.30 0.990 7.40 0.013 1.28 1.22 9.99 a. all yields over 98% Figure 2-5. Plot of [ 3H]/[ 3D] vs. [THF]/[THF-d8] kH/ kD THF-d8 = Slope = 7.87 ( 0.38) Intercept = 0.140 ( 0.296) THF vs THF-d8y = 7.8714x + 0.1403 R2 = 0.9909 0 2 4 6 8 10 12 00.20.40.60.811.21.4 [THF]/[THF-d8][3 H ]/[3 D ]

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29 Table 2-4. Rate constants for H-atom abstractions H-Donor kH/kD in H2O 103 kH/M-1s-1 a in H2O 103 kH/M-1s-1 b n -C4F9 in BTB 63 CH3OH 0.43 1.8 0.92 CH3CH2OH 2.8 12 3.0 (CH3)2CHOH 11.4 48c 16 (CH2OH)2 1.28 5.4 (CH3CHOH)2 5.6 24 5.0 CH3CO2CH2OH 0.59 2.5 CF3CH2OH 0.019 0.08 (CF3)2CHOH 0.094 0.39 THF 7.9 33d 31 (CH3OCH2)2 1.3 5.5 6.7 CH3COCH3 0.015 0.06 CH3CO2H 0.005 0.02 CH3CH2CO2H 0.18 0.76 CH3CO2 Na+ 0.028 0.12 CH3CH2CO2 Na+ 0.36 1.5 HSCH2CH2SO3 Na+ 96 400 (HOCH2CH2CH2)3SiH 28 120 BrMe3N+CH2SiMe2H 20.5 86 H3PO3 3.5 15 a. Based on kD = 4.2 x 103M-1 s-1 b. From reference 55 c. LFP gave kH = 40 x 103 M-1s-1 d. Value determined by LFP probe experiment and upon which all other rates are based

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30 2.3 Discussion of the Kinetic Data Before considering the kH rate constants in Table 2-4 it is imperative to establish that the kH/kD ratios are not influenced by: (i) th e small protic impurity in the (99.5%) THF-d8, nor (ii) proton transfer from the water solven t to the fluoroalkyl radical. With regard to (i), since kH/kD = 7.9 for THF/THF-d8, (Figure 2-5) plots of 3H/3D versus [H-Donor]/[THF-d8] are expected to have a positive in tercept, which will partially derive from the H-content in the THF-d8. In a control experiment with THF-d8 alone, an intercept of 7.9 x 0.5% = 0.04 was expected due simply to the H-content of the THF-d8. This was confirmed when a 3H/3D ratio of 0.04-0.05 was observed. Therefore, non-zero intercepts do not compromise the accuracy of the slopes of these plots, from which kH/kD values are determined. The non-zero intercepts are a result of experi mental error and the small H-content in THF-d8. In regard to (ii), one can at least imagine that some 3D might be replaced by 3H via an electron transfer from THF-d8 to RfSO3 yielding a perfluoroalkyl anion which would be rapidly protonated by water to yield 3H/3D ratios which show a larger H-atom abstraction contribution, and would result in erroneous, large 3H/3D ratios (Scheme 2-7). Scheme 2-7. Possible el ectron transfer mechanism O d8 + Na O3SCF2CF2OCF2CF2 O d8 H2O Na O3SCF2CF2OCF2CF2 + Na O3SCF2CF2OCF2CF2 +H+ Na O3SCF2CF2OCF2CF2H 3H

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31 The electron transfer reactions can be ruled out by the results described in (i) for THF-d8 alone in water yielding only the expected H-im purities. They were more firmly ruled out by showing than no 3D was produced in a reaction carried out with THF in D2O. 2.3.1 Rate Constants for H-Atom Abstractions in Water by Primary Fluoroalkyl Radicals Rate constants for the eight alcohols show the expected response to structural factors in terms both of C-H bond dissociation enthalpies (BDEs) and inductive effects. Thus, the increase in kH along the series CH3OH < CH3CH2OH < (CH3)2CHOH (Table 2-4) can be primarily attributed to a decrease in -C-H BDEs along the series (94, 93, and 91 kcal mol-1, respectively). 81 Comparison of the rate constants for methanol, ethanol, and isopropanol (1.8, 12, and 48 x 103 M-1 s-1, respectively, Table 2-4) with those reported for reaction of the CF3 radical with the same alcohols in water 82 8, 46, and 92 x 103 M-1 s-1, respectively, indicates that pr imary fluoroalkyl radicals are somewhat less reactive than trifluoromethyl radicals in H-atom abstractions, a reactivity difference which has been noticed previ ously for their addi tions to alkenes. 49 Rates of Hatom abstraction from the -CH position in alcohols are reduced by inductive electron withdrawing (EW) neighboring atoms or groups because EW disfavors the polar effects which can stabilize the transition state and, ther efore, enhance the reactivity of a substrate (see Figure 2-1). Thus, (CH2OH)2 and (CH3CHOH)2 are only half as reactive, respectively, as CH3CH2OH and (CH3)2CHOH, despite having twice as many -CH hydrogen atoms. Even larger rate retard ing polar effects ar e seen in the two fluoroalcohols which are only 0.7-0.8% as reactive as their non-fluorinated counterparts (Table 2-4). Rate constants for H-atom abstraction from carbon are also small for compounds containing EW carbonyl, ester, and carboxylic acid groups, some of which are so

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32 unreactive that they may be suitable as solv ents for chain reactions involving fluorinated radicals. The carboxylate anions are more reactive than the corresponding carboxylic acids. This result further sugge sts that polar effects play a ro le in stabilizing/destabilizing the transition state. Mainly, any rate re duction due to coulombic repulsion between the negative charges on the carboxylate anion and th e radicals sulfonate group is more than compensated for by the inductive electron donating ability of the CO2 group ( I = -0.10 vs. I = +0.34 for CO2H). 83 Not surprisingly, H-atom abstractions from ethers occur at rates comparable to the rates of abstraction from alcohols. THF is six times as reactive towards RfSO3 as (CH3OCH2)2. A six fold difference at -60C 84 (dropping to a two fold diff erence at 27 C) 85 has previously been reported for the rates of Hatom abstraction from THF and (CH3CH2)2O by t -butoxyl radicals. The greater r eactivity of THF was attributed to favorable stereoelectronic effects factors in which conjugative electron delocalization stabilizes the oxyalkyl radi cal reaction product and there by decreases the C-H BDE in THF relative to diethyl ether because of th e small dihedral angle between the oxygens lone pair of electrons and the -C-H bonds in THF. The water-soluble thiol and two water-sol uble silanes are sufficiently reactive towards RfSO3 that they may prove useful as chain transfer agents in fluoroalkyl radical chain reactions. 2.3.2 Comparison of Rate Constants for H-at om Abstraction by Primary Fluoroalkyl Radicals in Water and in BTB The four alcohols for which the comparison is possible have kH values 2-5 times greater in water than in BTB but the two ethe rs show no significant solvent effect on their kH values. It has previously been reported that primary fl uoroalkyl radicals add to the

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33 C=C double bonds of styrenes 5-9 times and to 1-alkenes 3 times more rapidly in water than in F113. 48,73 It was concluded that these modest rate enhancements derived from stabilization of the polar tr ansition state for addition of the electrophilic fluorinated radical to alkenes by the polar solvent, water. This is reasonable because the C=C double bond of styrenes and alkenes are readily polarized and the developing negative and positive charges in the transition state are well separated, and therefore can be solvated by water molecules (Figure 2-6). This is no t the case for a H-atom abstraction where any charge separation occurs over a much shorte r distance and the transition state is more reminiscent of an intimate ion pair (Figure 21) than a solvent sepa rated ion pair (Figure 2-6). Figure 2-6. Charge separated polar tran sition state for addition to C=C double bonds The absence of significant solvent eff ects on H-atom abstraction for hydrocarbons by t -butoxyl radicals was first proposed by Wa lling and coworkers in the early 1960s who observed that t -butanol/acetone product ratios, wh ich reflect competition between Hatom abstraction and -scission of the t -butoxyl radical, showed large solvent effects (Figure 2-7). 86-88 R'' r r r R'-CF2-CF2 R' = -O3SCF2CF2O (H2O) = CF3 (F113) R'' = phenyl, n -alkyl r = H, CH3, ect.

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34 Figure 2-7. Competing Hatom abstraction and -scission pathways It was argued that solvent interacti on with the polar transition state for -scission was plausible, but the transition state for H-atom abstraction would be sterically crowded and not allow solvation by the polar solvent. 86 Accordingly, the increased acetone formation in polar solvents was attributed to s olvation of the transition state for the -scission process. 88 This analysis was proven correct 30 y ears later when direct, time resolved, LFP kinetic measurements showed that ther e was no kinetic solvent effect on H-atom abstraction from cyclohexane by t -butoxyl radicals. 89 The absence of a kinetic solvent effect on H-atom abstraction from hydrocarbons by t -butoxyl radicals and its expl anation provides a rationale fo r the rate constants for Hatom abstraction from the two ethers by the fluoroalkyl radical in water and BTB being essentially equal (Table 2-4). However, the alcohols seem to show a m odest 2-5 fold rate enhancement in water vs. BTB for H-atom abstraction (Table 2-4). The observed accelerated rates may be due to hydrogen bond formation between the hydr oxyl group of the alcohol and a water molecule (Figure 2-8). C O R-H kHk C OH O

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35 Figure 2-8. Hydrogen bonding of an alcohol to a water molecule This will increase the electron density on the oxygen atom and stabilize the developing radical center by conjugative electr on delocalization, thus lowering the BDE of the -hydrogens and allowing for more rapid H-atom abstractions. 2.4 Conclusions It was known that the rates of addition of fluorinated primary alkyl radicals to C=C double bonds are larger by a factor of 3-9 in water than in a solvent of low polarity. 73 Now it has been discovered that the rates of H-atom abstraction by these radicals from alcohols are only 2-5 times faster in water than in a low pol arity solvent. Moreover, Hatom abstraction form ethers is unaffected by solvent polarity, a result consistent with earlier work on H-atom ab straction from hydrocarbons by t -butoxyl radicals. 86-89 Other than the success of developing a method to obtain absolute rate constants for H-atom abstractions by water soluble fluoroalkyl radicals, the fi nal conclusion is that the reactivities of these radicals can only be modul ated to a minor extent by solvent polarity. 2.5 Experimental All reagents used (includi ng those of Table 2-4) were commercially available, except for the two silanes 90 in Table 2-4, and were purchas ed from CIL, Adrich, Fisher, or Lancaster. All reagents we re used without further purifi cation and all reaction solvents were dried via known methods. NMR spectra and kinetic 19F NMR measurements were performed at 282 MHz using a Varian VXR-300 spectrometer. All chemical shifts are C H O H OH H

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36 reported in ppm downfield from the internal standard, CFCl3. 1H NMR spectra were performed on the same instrument at 300 MHz, and chemical shifts are reported relative to the internal standard, TM S. Melting points were determined using a Thomas Hoover Capillary melting point apparatus. 2.5.1 Sodium 5-iodo-3-oxaocta fluoropentanesulfonate ( 1 ) A solution of NaOH (2.9850g, 74.63 mmol) in 20 mL of deionized water was prepared and stirred in a 100 mL round bottom flas k equipped with a reflux condenser. Tetrafluoro-2-(tetrafl uoro-2-iodoethoxy)ethanesulfonyl fluoride (ICF2CF2OCF2CF2SO2F, 15.8951g, 37.31 mmol) was added to the round botto m flask. The reaction mixture was allowed to stir for 12 hours at 90C. The water was removed by roto-evaporation, yielding a white solid. Compound 1 (see appendix) was dissolved in absolute ethanol to separate out the insoluble NaF. The etha nol was removed by roto-evaporation, and the title compound was recrystallized from water to give a 90% yield: m.p. 149 C, dec.; 19F NMR (D2O/CFCl3 in C6D6), -67.81 (s, 2F), -82.08 (t, 2F, J = 12.1 Hz), -85.82 (s, 2F), -117.90 (s, 2F). 73 2.5.2 Sodium 4-( -methyl)vinylbenzoate ( 2 ) 4-bromo-methylstyrene A 3-neck round bottom flask was equipped with a pressure equalizing funnel, stir bar, and a reflux condenser with nitrogen inlet. 100 mL of anhydrous THF along with ethyltriphenylphosphonium bromide (13.36g, 36 mmol) were charged to the flask and cooled to -5 C. n -BuLi (2.5 M in hexane, 14.5 mL, 36 mmol) was slowly added to the stirred solution via syringe resulting in a red soluti on which was stirred for 45 minutes. In a flask, 4-bromobenzaldehyde (5.55g, 30 mmol) was dissolved in 50 mL of anhydrous THF and added to the equalizing funnel. 4-bromobenzaldehyde was added drop wise

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37 over about 1 hour, and allowed to achieve room temperature with stirring over night. The reaction mixture was diluted with brine and extracted with three 100 mL portions of benzene. The combined organic layers we re dried with magnesium sulfate, and the benzene was removed by roto-evaporation yiel ding an oily semi-solid. The oil was dissolved in diethyl ether (50 mL) and the triphenylphosphonium oxide was filtered out. After removal of the diethyl ether, the oil was purified by column chromatography using hexanes as the mobile phase. The title co mpound was obtained as a colorless oil in 92% yield: 1H NMR (CDCl3, TMS), 7.37-7.44 (m, 2H), 7.14-7.20 (m,2H), [6.24-6.35 (m) + 5.82 (m)] (2H), 1.87 (m, 3H). 73 4-( -methyl)vinylbenzoic acid A 250 mL round bottom flask was equipped with a stir bar, and condenser with nitrogen inlet. 4-bromo-methylstyrene (2.9g, 14.6 mmol) was dissolved in 70 mL of THF and cooled to -78 C. The t -BuLi (1.7 M in pentane, 17.2 mL 29.3 mmol) was slowly added to the stirred solution via a syringe. The re sulting dark green solution was stirred for 2 hours at -78 C. CO2 gas was then bubbled into the solu tion to saturation via a pipette. The CO2 was generated by adding sodium carbonate to hydrochloric acid which was dried by passing the gas through concentrated sulfuric acid and calci um sulfate. Upon addition of the CO2, the green color changed to a light brown, staw color. The solution was allowed to achieve room temperature a nd stirred over night. The reaction mixture was then acidified to pH = 2 with 10% HC l, and extracted three times with 30 mL methylene chloride. The combined organic la yers were dried with magnesium sulfate, and the solvent was removed vi a roto-evaporation to give a white solid. The white solid was recrystallized in ethyl acetate to give a 94% yield of the title acid: 1H NMR

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38 (acetone-d6), 8.12-8.21 (m, 2H), 7.59-7.66 (m,2H), [6.54-6.65 (m) + 6.02 (m)] (2H), 2.02 (m,3H) 73 Sodium 4-( -methyl)vinylbenzoate ( 2 ) 4-( -methyl)vinylbenzoic acid (1.0g, 6.17 mmol) was dissolved in 8 mL of methanol in a 1 neck round bottom flask. NaOH (1 M in methanol) was added until a pH of 7 was obtained. The methanol was removed by roto -evaporation, and the resulting crystals were washed and dried with diethyl ether. Compound 2 was obtained in 62% yield: 1H NMR (D2O), 8.00-8.11 (m, 2H), 7.45-7.56 (m, 2H), [6.41-6.49 (m) + 5.93 (m)] (2H), 1.94 (m, 3H) 73 2.5.3 Sodium 5-H-3-oxaoctafluoropentanesulfonate ( 3 H ) ICF2CF2OCF2CF2SO3NaH2O (0.35g, .75 mmol) was added to a pyrex reaction vessel along with 50 mL of THF. The solution was degassed by bubbling nitrogen for 30 minutes. The solution was then ir radiated with UV for 24 hours. 19F NMR showed that the radical precursor had disappeared. The excess THF was removed via rotoevaporation to give a white so lid. The white solid was washed with hexanes, then diethyl ether, and dried under reduced pressure to give the title compound in 81% yield: 1H NMR (acetone-d6), 6.48 (tt, 1H, J1 = 3.4 Hz, J2 = 52 Hz); 19F NMR (acetone-d6, CFCl3), -81.6 (m, 2F), -88.7 (s, 2F), -117.6 (s, 2F), -138.2 (dt, 2F, J1 = 4.3 Hz, J2 = 51 Hz); HRMS 90 (FAB), (M + Na): calcd 342. 9263; found 342.9256. CHN 90 C4F8HNaO4SH2O: calcd C 14.21, H 0.89; found C 14.20, H 0.61%. 2.5.4 Kinetic Measurements by Time-R esolved Laser Flash Photolysis The apparatus and procedures ha ve been described elsewhere. 73, 92 The radical, RfSO3 was generated instantaneously by 308 nm LFP of aqueous solutions of the parent iodide ( 1 ) at ambient temperature. 91

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39 2.5.5 Verification of Probe Addition Rate Constant The rate constant for addition, kadd, to the spectr oscopic probe, 2 was obtained (duplicate runs) in the usual manner to give values of (3.9 0.5) x 107 and (4.0 1.0) x 107 M-1 s-1, mean 3.95 x 107 M-1 s-1, with a value of (3.3 0.3) x 107 M-1 s-1 reported previously. 73 In any set of experiments, the probes concentr ation was kept constant (Table 2-26) and grow in of the absorption at 320 nm was monitored. 91 2.5.6 Laser Flash Photolysis Probe Experiments The procedure has been descri bed in detail previously. 48, 79 1.5 mL of aqueous solutions (0.027 M) of IRfSO3Na, 1 in quartz cuvettes (8 x 8 mm) sealed with rubber septa were deaerated by flushing with N2 for 20 minutes, then the various amount (50-400 L) of deaerated THF or isopropanol and the vol ume of the sample was made up (when necessary) to 2.0 mL. After addition of 100 L of a stock solution (32.9 to 35.7 mM) of 2 the mixture was vortexed for 20 seconds a nd purged with nitrogen for a further 2-5 minutes. The growths of the optical density at 320 nm following each of 6 to 9 pulses of 308 nm laser were recorded for each concen tration of H-atom donor. These growth traces of the radical were analyzed by leas t squares fitting on the basis of psuedo-firstorder kinetics to obtain expe rimental rate constants, kexp. As described in the results, the experimental rate constant is the sum of the rate constants for all competitive processes.79, 91 2.5.7 General Procedure for Kinetic Competition Studies The kinetic studies were run in pyrex NMR tubes containing a sealed capillary tube (CFCl3 in C6D6) as the internal standard. For each kinetic study, a group of samples were prepared at the same time. The NMR tube s were capped with rubber septa and wrapped with Teflon tape before ch emicals were added. The IRfSO3Na was used as a stock

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40 solution (17.8% by weight) and added to the NM R tubes with a micro-syringe. All liquid chemicals were added with syringes and weighed on a balance. The samples were degassed by three freeze-pump-thaw cycles. After 19F NMR spectra were taken, the samples were irradiated using a RPR-204 Ra yonet photochemical reactor (254 nm). The 19F NMR were taken again after 24 hours. The NMR acquisition time was at least 15 minutes to assure accurate in tegration. The product ratios we re obtained from the ratios of integration of the CF2H and CF2D signals (see appendix). The conversion and yield were obtained from the integration of the CF2I peak in the starting material and the reduced product peaks relative to the internal standard. Tables and plots of kinetic data are given in section 2.5.8.

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41 2.5.8 Tables of Kinetic Data and Plots Table 2-5. Rate data for THF/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [THF]/[THF-d8] [ 3H]/[ 3D] a 0.013 1.29 0.204 1.67 0.013 1.28 0.415 3.47 0.013 1.28 0.605 5.03 0.013 1.28 0.809 6.68 0.013 1.30 0.990 7.40 0.013 1.28 1.22 9.99 a. all yields over 98% Figure 2-9. Plot of [ 3H]/[ 3D] vs. [THF]/[THF-d8] kH/ kD THF-d8 = Slope = 7.87 ( 0.38) Intercept = 0.140 ( 0.296) R2 = 0.991 THF vs THF-d8y = 7.8714x + 0.1403 R2 = 0.9909 0 2 4 6 8 10 12 00.20.40.60.811.21.4 [THF]/[THF-d8][3 H ]/[3 D ]

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42 CH3OH vs THF-d8y = 0.4342x + 0.1733 R2 = 0.9989 0 0.5 1 1.5 2 2.5 3 3.5 1.52.53.54.55.56.57.5 [CH3OH]/[THF-d8][4 H ]/[4 D ] Table 2-6. Rate data for CH3OH/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [CH3OH]/[THF-d8] [ 3H]/[ 3D] a 0.012 1.19 2.40 1.23 0.012 1.19 4.55 2.13 0.012 1.18 5.60 2.58 0.012 1.20 6.56 3.05 a. all yields over 98% Figure 2-10. Plot of [ 3H]/[ 3D] vs. [CH3OH]/[THF-d8] kH/ kD THF-d8 = Slope = 0.434 ( 0.010) Intercept = 0.173 ( 0.051) R2 = 0.999

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43 Table 2-7. Rate data for CH3CH2OH/THF-d8 competition [IRfSO3Na] (mol L-1) [CH3CH2OH]/ (mol L-1) [CH3CH2OH]/[THF-d8] [ 3H]/[ 3D] a 0.0108 .807 .735 2.54 0.0108 1.11 1.02 3.45 0.0108 1.57 1.44 4.72 0.0108 1.87 1.72 5.29 0.0108 2.15 1.95 6.00 0.0108 2.46 2.25 6.86 a. all yields over 98% Figure 2-11. Plot of [ 3H]/[ 3D] vs.[CH3CH2OH]/[THF-d8] kH/ kD = Slope = 2.81 (.069) Intercept = .549 (.111) R2 = .998 Ethanol vs THF-d8y = 2.805x + 0.5487 R2 = 0.9976 1.5 2.5 3.5 4.5 5.5 6.5 7.5 0.50.70.91.11.31.51.71.92.12.32.5[EtOH]/[THF-d8][3 H ]/[3 D ]

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44 Table 2-8. Rate data for (CH3)2CHOH/THF-d8 competition a. all yields over 98% Figure 2-12. Plot of [ 3H]/[ 3D] vs. [(CH3)2CHOH]/[THF-d8] kH/ kD = Slope = 11.4 (.2) Intercept = .270 (.086) R2 = .999 [IRfSO3Na] (mol L-1) [(CH3)2CHOH] (mol L-1) [(CH3)2CHOH]/ [THF-d8] [ 3H]/[ 3D]a 0.0108 .138 .127 1.60 0.0108 .253 .229 2.94 0.0108 .356 .322 4.04 0.0108 .595 .541 6.43 0.0108 .706 .649 7.74 0.0108 .825 .753 8.78

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45 Table 2-9. Rate data fo r ethylene glycol/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [ethylene glycol]/ [THF-d8] [ 3H]/[ 3D] a 0.012 1.20 0.313 0.557 0.012 1.22 0.607 0.963 0.012 1.20 0.913 1.38 0.012 1.19 1.33 1.97 0.012 1.19 1.76 2.47 0.012 1.19 2.35 3.16 a. all yields over 98% Figure 2-13. Plot of [ 3H]/[ 3D] vs. [ethylene glycol]/[THF-d8] kH/ kD THF-d8 = Slope = 1.28 ( 0.03) Intercept = 0.195 ( 0.040) R2 = 0.998 Ethylene Glycol vs THF-d8y = 1.2825x + 0.1954 R2 = 0.998 0 0.5 1 1.5 2 2.5 3 3.5 00.511.522.5 [Ethylene Glycol]/[THF-d8][3 H ]/[3 D ]

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46 Table 2-10. Rate data for 2,3-butanediol/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [2,3-butanediol]/ [THF-d8] [ 3H]/[ 3D] a 0.013 1.33 0.162 1.23 0.013 1.33 0.348 2.36 0.013 1.33 0.524 3.42 0.013 1.33 0.696 4.58 0.013 1.33 0.870 5.21 0.013 1.32 1.05 6.14 a. all yields over 98% Figure 2-14. Plot of [ 3H]/[ 3D] vs. [2,3-butanediol]/[THF-d8] kH/ kD THF-d8 = Slope = 5.55 ( 0.23) Intercept = 0.449 ( 0.155) R2 = 0.993 2,3-Butanediol vs THF-d8y = 5.5469x + 0.449 R2 = 0.9933 0 1 2 3 4 5 6 7 00.20.40.60.811.2 [2,3-Butanediol]/[THF-d8][3H]/[3D]

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47 Table 2-11. Rate data fo r methyl glycolate/THF-d8 competition a. all yields over 98% Figure 2-15. Plot of [ 3H]/[ 3D] vs. [methyl glycolate]/[THF-d8] kH/ kD THF-d8 = Slope = 0.593 ( 0.028) Intercept = 0.328 ( 0.067) R2 = 0.991 [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [methyl glycolate]/ [THF-d8] [ 3H]/[ 3D]a 0.011 1.19 0.405 0.450 0.011 1.20 0.816 0.804 0.011 1.21 1.24 1.15 0.011 1.19 2.09 1.66 0.011 1.17 3.04 2.14 0.011 1.17 4.33 2.83 Methyl Glycolate vs THF-d8y = 0.5927x + 0.328 R2 = 0.9912 0 0.5 1 1.5 2 2.5 3 3.5 012345 [Methyl Glycolate]/[THF-d8][3H/3D]

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48 Table 2-12. Rate data for CF3CH2OH/THF-d8 competition a. all yields over 98% Figure 2-16. Plot of [ 3H]/[ 3D] vs. [CF3CH2OH]/[THF-d8] kH/ kD THF-d8 = Slope = 0.0188 ( 0.0007) Intercept = 0.0803 ( 0.0085) R2 = 0.994 [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [ CF3CH2OH] [THF-d8] [ 3H]/[ 3D] a 0.011 0.232 4.27 0.158 0.011 0.223 6.69 0.203 0.011 0.223 8.82 0.260 0.011 0.221 11.1 0.286 0.011 0.218 14.6 0.348 0.011 0.218 17.9 0.421 CF3CH2OH vs THF-d8y = 0.0188x + 0.0803 R2 = 0.9939 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 38131823 [CF3CH2OH]/[THF-8][3H/3D]

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49 Table 2-13. Rate data for (CF3)2CHOH/CD3OD competition [IRfSO3Na] (mol L-1) [CD3OD] (mol L-1) [(CF3)2CHOH]/ [CD3OD] [ 3H]/[ 3D] a 0.011 2.20 0.314 0.121 0.011 2.16 0.473 0.472 0.011 2.20 0.617 0.872 0.011 2.18 0.779 1.30 0.011 2.19 0.971 1.87 0.011 2.19 1.16 2.11 a. all yields over 98% Figure 2-17. Plot of [ 3H]/[ 3D] vs. [(CF3)2CHOH]/[CD3OD] kH/ kD CD3OD = Slope = 2.47 ( 0.12) Intercept = -0.651 ( 0.093) R2 = 0.991 (CF3)2CHOH vs CD3ODy = 2.4685x 0.6507 R2 = 0.9906 0 0.5 1 1.5 2 2.5 0.20.40.60.811.21.4 [(CF3)2CHOH]/[CD3OD][3H/3D]

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50 Table 2-14. Rate data for CH3OCH2CH2OCH3/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [(CH3OCH2)2]/ [THF-d8] [ 3H]/[ 3D] a 0.011 1.07 0.414 0.792 0.011 1.06 0.807 1.35 0.011 1.07 1.18 1.88 0.011 1.07 1.58 2.35 0.011 1.07 1.95 2.82 0.011 1.06 2.34 3.35 a. all yields over 98% Figure 2-18. Plot of [ 3H]/[ 3D] vs. [CH3OCH2CH2OCH3]/[THF-d8] kH/ kD THF-d8 = Slope = 1.31 ( 0.02) Intercept = 0.280 ( 0.030) R2 = 0.999 CH3OCH2CH2OCH3 vs THF-d8y = 1.3128x + 0.2806 R2 = 0.9991 0 0.5 1 1.5 2 2.5 3 3.5 4 00.511.522.5 [CH3OCH2CH2OCH3]/[THF-d8][3H/3D]

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51 Table 2-15. Rate data for (CH3)2CO/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [(CH3)2CO]/ [THF-d8] [ 3H]/[ 3D] a 0.012 1.19 2.39 0.0953 0.012 1.19 3.57 0.117 0.012 1.19 4.46 0.126 0.012 1.19 5.65 0.144 a. all yields over 98% Figure 2-19. Plot of [ 3H]/[ 3D] vs. [(CH3)2CO]/[THF-d8] kH/ kD THF-d8 = Slope = 0.0146 ( 0.0010) Intercept = 0.0619 ( 0.0043) R2 = 0.990 Acetone vs THF-d8y = 0.0146x + 0.0619 R2 = 0.99 0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 23456 [Acetone]/[THF-d8][3H/3D]

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52 Table 2-16. Rate data for CH3COOH/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [Acetic Acid]/ [THF-d8] [ 3H]/[ 3D] a 0.012 1.18 3.10 0.0542 0.012 1.19 4.45 0.0589 0.012 1.20 5.76 0.0676 0.012 1.19 7.23 0.0685 0.012 1.19 8.60 0.0756 0.012 1.18 10.0 0.0881 a. all yields over 98% Figure 2-20. Plot of [ 3H]/[ 3D] vs. [CH3COOH]/[THF-d8] kH/ kD THF-d8 = Slope = 0.00455 ( 0.00053) Intercept = 0.0391 ( 0.0037) R2 = 0.948 Acetic Acid vs THF-d8y = 0.0046x + 0.0391 R2 = 0.9483 0.04 0.05 0.06 0.07 0.08 0.09 0.1 24681012 [Acetic Acid]/[THF-d8][3H/3D]

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53 Table 2-17. Rate data for CH3COONa/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [CH3COONa]/ [THF-d8] [ 3H]/[ 3D] a 0.011 0.214 3.53 0.182 0.011 0.217 4.62 0.225 0.011 0.217 5.78 0.277 0.011 0.217 6.94 0.308 0.011 0.214 9.70 0.381 0.011 0.212 12.2 0.431 a. all yields over 98% Figure 2-21. Plot of [ 3H]/[ 3D] vs. [CH3COONa]/[THF-d8] kH/ kD THF-d8 = Slope = 0.0284 ( 0.0020) Intercept = 0.0985 ( 0.0159) R2 = 0.979 CH3COONa vs THF-d8y = 0.0284x + 0.0985 R2 = 0.9793 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 2468101214 [CH3COONa]/[THF-d8][3H/3D]

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54 Table 2-18. Rate data for CH3CH2COOH/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [CH3CH2COOH]/ [THF-d8] [ 3H]/[ 3D] a 0.012 1.20 1.48 0.382 0.012 1.20 2.55 0.534 0.012 1.20 3.61 0.749 0.012 1.20 4.66 0.923 0.012 1.19 5.82 1.16 a. all yields over 98% Figure 2-22. Plot of [ 3H]/[ 3D] vs. [CH3CH2COOH]/[THF-d8] kH/ kD THF-d8 = Slope = 0.180 ( 0.006) Intercept = 0.0959 ( 0.0234) R2 = 0.997 CH3CH2COOH vs THF-d8y = 0.1804x + 0.0959 R2 = 0.9968 0.2 0.4 0.6 0.8 1 1.2 1.4 1234567 [CH3CH2COOH]/[THF-d8][3 H ]/[3 D ]

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55 Table 2-19. Rate data for CH3CH2COONa/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [CH3CH2COONa]/ [THF-d8] [ 3H]/[ 3D] a 0.013 1.28 0.288 0.181 0.013 1.29 0.484 0.265 0.013 1.29 0.778 0.373 0.013 1.29 1.13 0.464 0.013 1.28 1.42 0.610 a. all yields over 98% Figure 2-23. Plot of [ 3H]/[ 3D] vs. [CH3CH2COONa]/[THF-d8] kH/ kD THF-d8 = Slope = 0.362 ( 0.021) Intercept = 0.0820 ( 0.0190) R2 = 0.990 CH3CH2COONa vs THF-d8y = 0.3617x + 0.082 R2 = 0.9902 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 00.511.5 [CH3CH2COONa]/[THF-d8][3H/3D]

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56 Table 2-20. Rate data for HSCH2CH2SO3Na/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [HSCH2CH2SO3Na]/ [THF-d8] [ 3H]/[ 3D] a 0.011 0.677 0.174 20.1 0.011 0.677 0.232 27.3 0.011 0.675 0.291 29.1 0.011 0.673 0.349 38.9 0.011 0.675 0.408 41.0 0.011 0.682 0.460 48.7 a. all yields over 98% Figure 2-24. Plot of [ 3H]/[ 3D] vs. [HSCH2CH2SO3Na]/[THF-d8] kH/ kD THF-d8 = Slope = 96.0 ( 8.1) Intercept = 3.54 ( 2.70) R2 = 0.972 HSCH2CH2SO3Na vs. THF-d8y = 96.045x + 3.5449 R2 = 0.9723 10 15 20 25 30 35 40 45 50 55 0.130.230.330.430.53 [HSCH2CH2SO3Na]/[THF-d8][3H/3D]

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57 Table 2-21. Rate data for (HOCH2CH2CH2)3SiH/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [Silane]/ [THF-d8] b [ 3H]/[ 3D] a 0.0079 0.487 0.131 3.46 0.0079 0.479 0.160 4.04 0.0079 0.483 0.185 5.12 0.0079 0.485 0.211 5.74 0.0079 0.489 0.261 7.02 a. all yields over 98%; b. reference 90 Figure 2-25. Plot of [ 3H]/[ 3D] vs. [(HOCH2CH2CH2)3SiH]/[THF-d8] kH/ kD THF-d8 = Slope = 28.1 ( 1.6) Intercept = -0.258 ( 0.321) R2 = 0.990 (HOCH2CH2CH2)3SiH vs THF-d8y = 28.135x 0.2583 R2 = 0.9898 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 0.10.150.20.250.3 [(HOCH2CH2CH2)3SiH]/[THF-d8][3H/3D]

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58 Table 2-22. Rate data for Me3N+CH2SiMe2H Br-/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [Silane]/ [THF-d8] b [ 3H]/[ 3D] a 0.011 0.655 0.0673 1.01 0.011 0.671 0.164 3.05 0.011 0.662 0.333 6.85 0.011 0.672 0.492 9.63 a. all yields over 98%; b. reference 90 Figure 2-26. Plot of [ 3H]/[ 3D] vs. [BrMe3NCH2SiMe2H]/[THF-d8] kH/ kD THF-d8 = Slope = 20.5 ( 0.8) Intercept = -0.283 ( 0.245) R2 = 0.997 BrMe3NCH2SiMe2H vs THF-d8y = 20.516x 0.2827 R2 = 0.997 0 2 4 6 8 10 12 00.10.20.30.40.50.6 [BrMe3NCH2SiMe2H]/[THF-d8][3 H ]/[3 D ]

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59 Table 2-23. Rate data for H3PO3/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [H3PO3]/ [THF-d8] [ 3H]/[ 3D] a 0.011 1.08 0.271 1.73 0.011 1.09 0.536 2.79 0.011 1.09 0.804 3.68 0.011 1.09 1.07 4.79 0.011 1.09 1.34 5.46 0.011 1.09 1.61 6.43 a. all yields over 98% Figure 2-27. Plot of [ 3H]/[ 3D] vs. [H3PO3]/[THF-d8] kH/ kD THF-d8 = Slope = 3.48 ( 0.10) Intercept = 0.881 ( 0.109) R2 = 0.996 H3PO3 vs. THF-d8y = 3.4796x + 0.8811 R2 = 0.9964 0 1 2 3 4 5 6 7 00.511.52 [H3PO3]/[THF-d8][3H/3D]

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60 Table 2-24. Rate constants (kgl) for RfSO3 + 4-(1-propenyl)benzoate Na+, 2 in water [ 2 ] / M kex / s-1 [ 2 ] / M kex / s-1 4.43 x 10-3 2.00 x 105 5.89 x 10-32.38 x 105 3.64 x 10-3 1.38 x 105 4.16 x 10-31.81 x 105 2.82 x 10-3 1.15 x 105 3.21 x 10-31.32 x 105 1.94 x 10-3 1.09 x 105 2.21 x 10-31.08 x 105 1.38 x 10-3 6.53 x 104 1.68 x 10-37.27 x 104 9.99 x 10-4 4.61 x 104 slope a = 3.96 x 107 M-1 s-1 R2 = 0.9313 std err slope = 5.4 x 106 confidence interval b =1.0 x 107 slope a = 3.86 x 107 M-1 s-1 R2 = 0.9882 standard err slope = 2.4 x 106 confidence interval b =4.9 x 106 kgl = (4.0 1.0) x 107 M-1 s-1 kgl = (3.9 0.5) x 107 M-1s-1 a. slope of the plot of kex vs. [ 2 ], example Figure 2-2 in text. b. 90% confidence level.

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61 Table 2-25. LFP kinetic probe data yielding kH for THF [THF] / M kex / s-1 [ 2 ] / M kex kgl [ 2 ] / s-1 Entry 1 0.000 6.23E+04 1.57E-03 2.03E+03 0.184 7.13E+04 1.57E-03 1.10E+04 0.367 8.49E+04 1.57E-03 2.47E+04 0.730 9.56E+04 1.57E-03 3.54E+04 1.470 1.22E+05 1.57E-03 6.12E+04 slope a = 3.9E+04 R2 = 0.9800 std err slope= 3.2E+03 confidence interval b = 6.5E+03 kH = (3.9 0.7) x 104 M-1s-1

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62 Table 2-25. Continued: Entry 2 0.000 7.04E+04 1.70E-03 5.10E+03 0.129 7.35E+04 1.70E-03 8.22E+03 0.194 7.96E+04 1.70E-03 1.43E+04 0.290 7.99E+04 1.70E-03 1.47E+04 0.436 8.39E+04 1.70E-03 1.86E+04 0.653 8.96E+04 1.70E-03 2.43E+04 0.980 1.04E+05 1.70E-03 3.85E+04 1.470 1.18E+05 1.70E-03 5.24E+04 slope a = 3.2E+04 R2 = 0.9907 std err slope = 1.3E+03 confidence interval b = 2.4E+03 kH = (3.2 0.2) x 104 M-1s-1

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63 Table 2-25. Continued: Entry 3 0.000 8.33E+04 1.68E-03 1.89E+04 0.194 8.93E+04 1.68E-03 2.49E+04 0.290 9.22E+04 1.68E-03 2.78E+04 0.653 9.76E+04 1.68E-03 3.32E+04 0.980 1.14E+05 1.68E-03 5.00E+04 1.470 1.35E+05 1.68E-03 7.06E+04 slope a = 3.45E+04 R2 = 0.9707 std err slope = 3.0E+03 confidence interval b = 5.8E+03 kH = (3.5 0.6) x 104 M-1s-1

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64 Table 2-25. Continued: Entry 4 0.000 6.69E+04 1.62E-03 4.79E+03 0.201 7.66E+04 1.62E-03 1.45E+04 0.301 8.08E+04 1.62E-03 1.87E+04 0.452 8.44E+04 1.62E-03 2.23E+04 0.678 8.93E+04 1.62E-03 2.72E+04 1.016 9.92E+04 1.62E-03 3.71E+04 1.524 1.12E+05 1.62E-03 4.99E+04 2.287 1.39E+05 1.62E-03 7.66E+04 2.940 1.51E+05 1.62E-03 8.86E+04 slope a = 2.8E+04 R2 = 0.9938 std err slope = 8.5E+02 confidence interval b =1.6E+03 kH = (2.8 0.2) x 104 M-1s-1

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65 Table 2-25. Continued: entry 5 0.000 7.62E+04 1.70E-03 1.10E+04 0.201 7.94E+04 1.70E-03 1.42E+04 0.301 8.70E+04 1.70E-03 2.18E+04 0.452 9.30E+04 1.70E-03 2.78E+04 0.677 9.45E+04 1.70E-03 2.93E+04 1.016 1.13E+05 1.70E-03 4.78E+04 1.524 1.30E+05 1.70E-03 6.48E+04 2.940 1.67E+05 1.70E-03 1.02E+05 slope a = 3.2E+04 R2 = 0.9876 std err slope = 1.5E+03 confidence interval b = 2.7E+03 kH = (3.2 0.3) x 104 M-1s-1 a. slope of kexp vs. [THF], an example plot is gi ven in Figure 2-3 in the text. b. 90% confidence interval.

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66 Table 2-26. LFP kinetic probe data yielding kH for isopropanol [H-donor] / M kex / s-1 [ 2 ] / M kex kgl [ 2 ] / s-1 Entry 1 0.000 4.96E+04 1.40E-03 4.39E+03 0.478 6.56E+04 1.40E-03 1.17E+04 0.720 8.26E+04 1.40E-03 2.87E+04 1.080 9.47E+04 1.40E-03 4.07E+04 1.610 1.22E+05 1.40E-03 6.79E+04 2.420 1.46E+05 1.40E-03 9.19E+04 3.110 1.76E+05 1.40E-03 1.22E+05 Entry 2 0.000 7.20E+04 1.76E-03 4.07E+03 0.478 8.82E+04 1.76E-03 2.03E+04 0.720 9.88E+04 1.76E-03 3.09E+04 1.080 1.03E+05 1.76E-03 3.51E+04 1.610 1.22E+05 1.76E-03 5.41E+04 2.420 1.66E+05 1.76E-03 9.81E+04 3.110 1.94E+05 1.76E-03 1.26E+05

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67 Entry 1: slope a = 4.09E+04 R2 = 0.9945 std err slope = 1.2E+03 confidence interval b = 2.3E+03 kH = (4.1 0.2) x 104 M-1s-1 Entry 2: slope a = 3.95E+04 R2 = 0.9839 std err slope = 2.3E+03 confidence interval b = 4.3E+03 kH = (3.9 0.4) x 104 M-1s-1 a. slope of kexp vs. [isopropanol], an example plot is given in Figure 2-3 in the text. b. 90% confidence interval.

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68 CHAPTER 3 RATE CONSTANTS FOR OXYANI ON ACCELERATED HYDROGEN ABSTRACTION REACTIONS FROM ALKOXIDES BY A PERFLUOROALKYL RADICAL IN WATER 3.1 Introduction Shortly after Evans discovered huge rate accelerations exhibited by anionic oxyCope rearrangements (Figure 3-1), 93, 94 it was hypothesized that such accelerations were related to the bond weakeni ng effect of the anionic alkoxy group on the adjacent C3-C4 bond. 95 Figure 3-1. Anionic oxy-Cope re arrangement rate enhancement This basic conclusion from Goddards GVB th eory work has recently been confirmed and elaborated on by Houk 96 and Baumann 97 using density functional theory methodology. Houk has determined that the CH BDE of methoxide ion is ~23 kcal less than that of methanol. 96 The -C-H bond weakening effect observed for alkoxides should HO HO O M O M Oxy-Cope rearrangement Anionic oxy-Cope rearrangement Anionic rate enhancement of 1010-1017 !

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69 provide acceleration to other reactions that involve the br eaking of this same bond. Many such cases have been reported, 98 such as alkoxy accelerated [1.3]-sigmatropic rearrangements, 99, 100 the Ireland Claisen rearrangement of a llyl ester enolates, 101 and 1,5-hydrogen shifts. 102 In chapter two, competition methods using 19F NMR were employed to obtain the absolute rate constants for hydrogen atom ab straction for many organic hydrogen donors. As shown in Figure 3-2, isopropanol is fairly reactive towards perfl uoroalkyl radicals in both the non-polar solvent 1,3-bi s-trifluoromethylbenzene (BTB ) and in water. Modest rate enhancement is observed in water due to probable hydrogen bonding interactions between water and the hydroxyl gr oup weakening the C-H BDE. Figure 3-2. Isopropanol reac tivities in BTB and water Although polar, steric, and thermodynamic eff ects can have dramatic effects on the H-abstraction rates from orga nic compounds by fluorinated radicals, when working with a series of similar compounds, the relative rates of H-abstraction by O3SCF2CF2OCF2CF2 ( 4 ) correlate well with their rela tive C-H BDEs, as shown for the series of alcohols in water. The bond disso ciation energies of methanol, ethanol, and isopropanol in Table 3-1 were es timated by computational methods. 103 O3SCF2CF2OCF2CF2 C H OH 25 C, solventRf RfH C OH Rf Solvent kH CF3CF2CF2CF2 BTB H2O 1.6 x 104 M-1 s-14.8 x 104 M-1 s-1

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70 Table 3-1. Correlation between rate constant and calculated -C-H BDEs Alcohol kH / 103 M-1 s-1 krel (Per H) BDEs / kcal mol-1 CH3OH 1.8 (1) 93 CH3CH2OH 12 10 91 (CH3)2CHOH 48 80 89 As a result of the observed importance of BDEs on the abst raction of hydrogen atoms by perfluoroalkyl radicals and the many reported cases of C-H bond weakening effects of alkoxides, it was determined that the quantitative impact of the effects of alkoxide functional groups warranted invest igation. The only related previous work reported is that of Bunnett in which he found that methoxide ion was a good hydrogen atom donor to aryl radicals, 104, 105 being about 45 times more reactive than methanol for donation of a hydrogen atom to the p -nitrophenyl radical. 106 An immediate concern which arises in carrying out kinetic studies of hydrogen abstraction from alkoxides is that the al koxide substrate must be present in the competition mixture as a totally homogeneous solute, something that is impossible in both BTB and the aqueous medium, the latter because the basicitie s of alkoxides would preclude their existence in water. However, as part of the inve stigation into hydrogen atom abstraction by fluorinated radicals fr om alcohols in water, the absolute rate constants for H-atom abstraction from trifl uoroethanol and hexafl uoroisopropanol have been determined. Due to the polar and elec trostatic influence of fluorine substituents, these two fluorinated alcohols were many orde rs of magnitude less reactive than their hydrocarbon counterparts (Table 3-2).

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71 Table 3-2. Rate constants for hydrogen abstra ction from fluorinated and non-fluorinated alcohols Alcohol kH / 103 M-1 s-1 krel CH3CH2OH 12 CF3CH2OH 0.08 hydrocarbon 150 times more reactive (CH3)2CHOH 48 (CF3)2CHOH 0.39 hydrocarbon 123 times more reactive However slow the kinetics of these fluor inated alcohols may be towards hydrogen abstraction, they have one property which was extremely propitious in view of the afore mentioned interest in probing the kinetics of H-atom abstractions from alkoxides. Mainly, they are much more ac idic than their non-fluorinated counter parts, having pKas of 12.4 and 9.3 for trifluoroethanol and hexafluoroisopropanol, respectively. 107 Their conjugate bases, the alkoxides, would th erefore be relativel y weak, stable, and homogeneously soluble in water. 3.2 Results and Discussion 3.2.1 Kinetic Results Relative rate constants (kH/kD) for H-atom abstraction by O3SCF2CF2OCF2CF2 ( 4 ) from sodium trifluoroethoxide (TFEO, 5 ), sodium hexafluoroisopropoxide (HFIPO, 6 ), and sodium trifluoroisopropoxide (TFIPO, 7 ), were first determined by competition kinetics involving H-transfer fr om the alkoxide versus D-transfer from THF-d8 (Scheme 3-1). The same general procedur e was described in de tail previously in Chapter 2. The relative rate constants were easily converted to abso lute rate constants using the value of THF-d8s known rate constant, kD = 4.2 x 103 M-1 s-1, which was previously determined using laser flash phot olysis. The results obtained demonstrated

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72 that all three alkoxides are not only very much more reactive th an their respective alcohols, but that they are also consider ably more reactive th an the corresponding nonfluorinated alcohols (Table 3-3). O3SRfI h H2O O3SRf kHkDTHF-d8O3SRfH O3SRfD exclusively from exclusively from THF-d8 THF-d8CF3CH2O CF3CH2O CF3CH2O 4 5 5 3H3D 19F NMR = -138.3 ppm (dt)19F NMR = -139.0 ppm (m) Scheme 3-1. Competition scheme showing trifluoroethoxide ( 5 ) and THF-d8 Table 3-3. Absolute rate constants for alkoxides and co rresponding alcohols Alkoxide/Alcohol kH / 103 M-1 s-1 krel CF3CH2O Na+ ( 5 ) 77 CF3CH2OH 0.08 alkoxide 963 times more reactive (CF3)2CHO Na+ ( 6 ) 108 (CF3)2CHOH 0.39 alkoxide 277 times more reactive (CF3)(CH3)CHO Na+ ( 7 ) 155 (CF3)(CH3)CHOH 1.5 alkoxide 103 times more reactive This high reactivity undoubtedly derives fr om a combination of the bond-weakening effect of the alkoxide functional group and the enhanced nucleophilicity of the alkoxide C-H bond towards the highly elec trophilic perf luoro radical. LFP measurements were used to verify the observed results in the competition experiments for alkoxides. The LFP measurem ents of the rate constants for H-atom

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73 abstraction by O3SCF2CF2OCF2CF2 from TFEO ( 5 ) and HFIPO ( 6 ) met with mixed success. For TFEO the LFP value of kH was 11 x 104 M-1 s-1, which is in reasonable agreement with the 7.7 x 104 M-1 s-1 obtained by competition, as reported in Table 3-3. However, for HFIPO the observed LFP kH was 50 x 104 M-1 s-1, which is 4.5 times greater than the compe tition value of 11 x 104 M-1 s-1. The reasoning for the contradiction in rate values for HFIPO may rest in the fact that both H-bonding and ion pairing (with the metal counterion) are know n to cause large variations in alkoxide accelerated rate constants. 100 Other kinetic results seem to show that alkoxide accelerated processes are very sensitive to anything which influences the degree of free charge on the alkoxide. 93 As a result of this contradiction of rate constants for HFIPO, additional competition experiments were designed to validate the competition method for this system. First a direct competition between the two alkoxides using sodium 2-deuteriohexafluoroisopropoxide ( 8 ) in competition with sodium trifluoroethoxide (TFEO, 5 ), with no THF being involved was carri ed out. (Scheme 3-2). Scheme 3-2. Competition with no THF-d8 Combining this measured kH/kD value (4.64) with the value of the primary isotope effect (kH/kD = 5.88) for Hvs. Dabstraction from HFIPO, and using the rate constant of O3SRf 4 CF3CH2O 5 (CF3)2CDO 8 H2O O3SRfH 3HO3SRfD 3DNo THF-d8 involved

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74 7.7 x 104 M-1 s-1 for TFEO hydrogen abstraction, yields a rate constant (kH) for HFIPO of 9.8 x 104 M-1 s-1 (Equation 3-1). Equation 3-1. Calculation of kH (HFIPO) without using THF-d8 Secondly, a reverse competition experiment was carried out, using deuterated HFIPO ( 8 ) and undeuterated THF. This gave a kH/kD value of 1.94, which when combined with the kH value for THF (3.3 x 104 M-1 s-1) and the HFIPO isotope effect (kH/kD = 5.88) provides a value of kH for HFIPO of 10 x 104 M-1 s-1 (Equation 3-2). Equation 3-2. Calculation of kH (HFIPO) using a reverse competition k H(TFEO) kD(HFIPO-d) = 4.64 ; k H(HF I PO) kD(HFIPO-d) = 5.88 and kH(TFEO) = 7.7 x 104 M-1s-1 ; therefore kD(HFIPO-d) = 4.64 7.7 x 104 M-1s-1kD(HFIPO-d) = 1.66 x 104 M-1s-1; and using 5.88 kH(HFIPO) = 9.8 x 104 M-1s-1 k H(THF) kD(HFIPO-d) = 1.94 ; k H(HF I PO) kD(HFIPO-d) = 5.88 and kH(THF) = 3.3 x 104 M-1s-1 ; therefore kD(HFIPO-d) = 1.94 3.3 x 104 M-1s-1kD(HFIPO-d) = 1.70 x 104 M-1s-1; and using 5.88 kH(HFIPO) = 10.0 x 104 M-1s-1

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75 There is therefore a self cons istency in the values of kH for HFIPO that were obtained from the three different comp etition studies (11, 9.8, and 10 x 104 M-1 s-1), and we feel confident that their average, 10.8 x 104 M-1 s-1, can be regarded as a reliable value for the kH of HFIPO. Aldehyde hydrates and their monosodium salts are also of interest and relevant to the present work because they can be regarded as -hydoxy-substituted alcohols and alkoxides. Again, in order to study such comp ounds in water, one must have aldehyde hydrates that exist virtually 100% in the hydrate form when in water, and are acidic enough that their monobasic forms are stable in water. Chloral and fluoral hydrate meet these requirements nicely because the presence of the three -chlorines or fluorines insures that the hydrates are ex clusively present in water, an d that they are sufficiently acidic enough to cleanly form their monosodium salts upon treatment with one equivalent of NaH (Scheme 3-3). CCl3CH(OH)2CF3CH(OH)2pKa108 = 10.1 pKa108 = 10.2 1.0 eq. NaH 1.0 eq. NaH diethyl ether diethyl ether 0 C 0 C Cl3C F3C H OH O H OH O Na+Na+9 10 Scheme 3-3. Preparation of the monobasic sodium salts In fact the pKas of chloral and fluoral hydrate have been estimated to be 10.1 and 10.2, respectively. 108 Because the inductive effect of the three -halogens destabilizes the transition state, these hydrat es, like fluorinated alcohols, should be poor H-atom donors

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76 to O3SCF2CF2OCF2CF2. This is the cas e as shown in Table 3-4, which shows that chloral hydrate is slightly more reactive than fluoral hydrate, which slightly more reactive than trifluoroethanol, results which are c onsistent with stabilization of the carbon centered radicals formed from the hydrates by the extra -hydroxy group. More significantly, the monosodium salt of fluoral hydrate exhibits the la rgest enhancement, relative to its non-alkoxy counterpart (krel = 1315), as well as the larg est rate constant that has yet to be observed for H-atom abstraction fr om carbon to the fluorinat ed radical, O3SCF2CF2OCF2CF2 (kH = 1.7 x 105 M-1 s-1). Table 3-4. Absolute rate constants of hydrates and monobasic hydrate anions Hydrate / Hydrate monoanion kH / 103 M-1 s-1 krel CCl3CH(OH)2 0.83 Cl3C H OH O Na+9 157 189 CF3CH(OH)2 0.13 F3C H OH O Na+10 171 1315 CF3CH2OH 0.08

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77 3.2.2 Possible Synthetic Applications As mentioned in the introducti on to chapter one, chemists have been interested in developing synthetically useful free radical reactions. However, there has not been much attention paid to utilizing fluorinated free radical intermediates in synthesis. Such synthetic efforts so far have been reported by Paleta. 109 He has shown that by taking advantage of low BDEs of mainly alcohols and ethers, one can initiate nucleophilic radical additions by UV irradiation and furthe r improve yields through the use of a photosensitized process involv ing acetone (Figure 3-3) 109 Figure 3-3. Photo-sensitized additio n of alcohols and cyclic ethers The yields for the reactions in Figure 3-3 are all 90-97%, which in dicates a very good chain process. It is worth no ting that all of Paletas addi tions are to electron deficient olefins, probably to better match the SOMO-LUMO energy gap. We found the possibility of using CF3CH(OH)O ( 10 ) in Paletas radical chain process intriguing because adding CF3 groups via alkene additi on would be synthetically useful. The reactivity of CF3CH(OH)O ( 10 ) should be much greater than THF according to the kinetic data showing that 10 is 5 times more reactive than THF towards CH2=CH-C6F13 hv hvO CH3CHCH3OH CH3CH2OHOO O CH2CH2-C6F13 CH3CCH2-CH2-C6F13OH CH3 CH2-C-CH2CH-C6F13OH O O CH2CH2C6F13 acetone acetone

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78 hydrogen atom abstraction by the water soluble fluoroalkyl radical. With this goal in mind, many addition experiments were attempted in which 10 was added with different alkenes in different solvent systems. In addition, many initiation methods were attempted including the method develope d by Paleta (Scheme 3-4). Scheme 3-4. Attempted alkene addition of 10 The results of many experiments are given in Table 3-5, and show that we were not successful in propagating a chain process. The general procedure for all of these reactions involves dissolving th e alkoxide hydrate in the suit able solvent and adding the appropriate alkene. 5 mol% of the initiat or was added and the reaction mixture was heated in cases where heati ng was required for initiation. 19F NMR was monitored for indications that an addition ha d occurred, but from the results in Table 3-5, this was never the case. It is hard to imagine that the labile hydrogen atom of CF3CH(OH)O was not abstracted by one of these in itiation methods, therefore, th e probability is high that the resulting radical does not a dd to any of the alkenes studied. One possibility for the seemingly unreactive carbon centered radical is that it may too stable to add to any alkene. It is not difficult to envisi on a capto-dative scenario in which the CF3 group acts as the capto portion and the oxygen anion as the dative por tion. Such stabilization of radicals is well known to exist for similar electronic situations. F3CH OH O Na+10 hv, acetone H2O CO2 +NaF3CCH2CH2CH2CH2COO OH O Na+ 2

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79 Table 3-5. Summary of attempted chain propagation reactions with 10 Alkene Initiation Acetonitrile a DMF a D2O a AIBN x x Bz2O2 x x hv x x hv, acetone x x 1-octene hv, Bz2O2 x x AIBN x x Bz2O2 x x hv x x hv, acetone x x CN hv, Bz2O2 x x AIBN x x Bz2O2 x x hv x x hv, acetone x x styrene hv, Bz2O2 x x hv, acetone x CO2 2 ACVAb x hv, acetone x O2C ACVAb x a. x indicates no reaction; b. 4,4-azobis(4-cyanovaleric acid)

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80 Another possibility to take a dvantage of the low BDEs of -trifluoromethyl alkoxides was afforded by compound 11 (Scheme 3-5). Scheme 3-5. Dissociation of compound 11 Scheme 3-6. Synthesis of compound 11 Compound 11 was synthesized as shown in Scheme 3-6, and was envisioned as a thermal or photochemical free radical initia tor for polymerizations. Compound 11 should be susceptible to homolytic bond cleavage, as s hown in Scheme 3-5, due to the stabilizing O CF3 or hvO CF3 11 O CF3 11 MgCl O OEt F3C -78 C diethyl ether O CF3 60% H2NN(Me)2ethanol cat. acetic acidN N CF3 Ph 80% 1. n-BuLi 2. MeI THFN N CF3 Ph 85% CF3 Ph O 20% HCl diethyl ether 79% 1. LAH 2. H2OCF3 Ph OH 96% NaH diethyl ether

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81 effect that the CF3 and O have on the formed radical. Known compound 11 was synthesized by methods repor ted in recent literature. 110 Upon its synthesis, compound 11 was dissolved in DMF and subjected to UV light (254 nm). There was some evidence of bond scrambling because 11 exists as a diasteriomeric mixture, (9:1) and photolysis resulted in the ratio changing to 6:4 after only a few hours. Encouraged by these results, styrene was added into the reaction cylinder but resulted in no observed polymerization. From a pyrolysis point of view, 11 did not seem to undergo bond scrambling even though it was subjected to temperatures of 180 C. After these discouraging results, 11 was no longer studied as a possible free radical initiator. 3.3 Conclusions The alkoxide functionality has long been known to provide acceleration to sigmatropic processes where a bond to the ca rbon bearing the alkoxy group is broken. Absolute rate data now demonstrate that an -alkoxide also dramatically enhances homolytic hydrogen atom abstractions by highly electrophilic pe rfluoro radicals. Therefore, -fluorinated alkoxides exhibit bimolecula r rate constants fo r H-abstraction by a fluorinated radical in the 105 M-1 s-1 range, such rates representing enhancements relative to their re spective alcohols of between 100 and 1000-fold, depending on the reactivity of the alkoxide. The monobasic sodium salts of chloral and floral hydrate exhibit similar rate enhancements, relative to their respective hydrates. The extremely large absolute rate constant associated with the monobasic sodium salt of fluoral hydrate (171 x 103 M-1 s-1) for H-atom abstraction led to an attempted alkene addition synthetic application. However, there proved to be a problem associated in the attempted chain process.

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82 3.4 Experimental All reagents used were commercially av ailable, and were purchased from CIL, Aldrich, Fisher, or SynQuest. All reagents we re used without further purification, and all anhydrous solvents were dried according to well known methods. NMR spectra and kinetic 19F NMR measurements were performed at 282 MHz using a Varian VXR-300 spectrometer. All 1H NMR spectra were performed at 300 MHz on the same instrument. All chemical shifts are reported downfield in ppm from the internal standards, CFCl3 and TMS, for fluorine and proton NMR, respectively. 3.4.1 Typical Procedure for Prepar ation of Alkoxide Sodium Salts Hexafluoroisopropoxide, sodium salt ( 6 ): NaH (0.534 g, 22 x 10-3 mol) was suspended in 30 mL of anhydrous diethyl ether under nitrogen. The suspension was stirred a nd cooled to ice bath temperature. Hexafluoroisopropanol (3.1 g, 31 x 10-3 mol) was added to 15 mL of anhydrous diethyl ether and then added dropwise via an equali zing addition funnel to the NaH suspension. The solution was allowed to stir for 3 hours during which time it reached room temperature. The ether was removed by roto -evaporation and the resulting white solid was dried via vacuum pump overnight to obtain hexafluoroisopropoxide, sodium salt (2.66 g, 98.2% yield): 1H NMR (300 MHz, D2O) 4.42 (hept, JHF = 6.9 Hz, 1H); 19F NMR (282 MHz, D2O) -76.58 (d, JFH = 6.5 Hz, 6F). Trifluoroethoxide, sodium salt ( 5 ): White solid was obtained following the sa me general procedure (96% yield): 1H NMR (300 MHz, D2O) 3.93 (m, 2H); 19F NMR (282 MHz, D2O) -77.16 (m, 3F). Trifluoroisopropoxide, sodium salt ( 7 ):

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83 White solid was obtained following the sa me general procedure (96% yield): 1H NMR (300 MHz, D2O) 1.32 (m, 3H), 3.56 (m, 1H); 19F NMR (282 MHz, D2O) -80.48 (m, 3F). 3.4.2 Preparation of 2-deuteriohexa fluoroisopropoxide, sodium salt ( 8 ) 18 mL of lithium aluminum deuteride (1 M in diethyl ether, 0.018 mol) was added to 20 mL of stirred anhydrous diethy l ether under nitrogen. The su spension was cooled to -78 C and excess hexafluoroacetone was bubbled th rough the solution. The temperature was gradually allowed to achieve room temperatur e over night. The reaction was carefully quenched with 50 mL of water, washed with 3 x 20 mL portions of sodium potassium tartrate, and extracted with 3 x 30 mL of di ethyl ether. The orga nic layer was washed with 2 x 50 mL portions of brine. The organi c layer was dried with magnesium sulfate. The resulting alcohol was added dropwise to a stirred suspension of NaH (0.24 g 0.01 mol) in anhydrous diethyl ether at ice bath te mperature. The solution was allowed to stir for 3 hours during which time it reached room temperature. The ether was removed by roto-evaporation and the resulting white solid was dried via vacuum pump overnight to obtain the title com pound (1.57g, 82% yield): 19F NMR (282 MHz, D2O) -76.54 (s, 6F). 3.4.3 Typical Procedure for th e Preparation of Monobasic Sodium Salts of Hydrates Chloral hydrate, sodium salt ( 9 ) NaH (0.290 g, 12 mmol) was suspended in 30 mL of anhydrous diethyl ether under nitrogen. The suspension was stirred and cooled to ice bath temperature. Chloral hydrate (2.0 g, 12 mmol) was added to 15 mL of anhydrous diethyl ether and then added dropwise via an equalizing addition funnel to the NaH suspension. The solution was allowed to stir for 3 hours during which time it reached room temperature. The ether was removed by roto-evaporation and the resulti ng white solid was dried via vacuum pump

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84 overnight to obtain chloral hydrate, sodium salt (2.20 g, 97% yield): 1H NMR (300 MHz, D2O) 4.19 (s, 1H). Fluoral hydrate, sodium salt ( 10 ): The same general procedure was used to obtain a white solid (1.87 g, 95% yi eld): 1H NMR (300 MHz, D2O) 5.28 (q, JHF = 7.1 Hz, 1H); 19F NMR (282 MHz, D2O) -85.58 (d, JFH = 6.6 Hz, 3F). 3.4.4 General Procedure for 19F NMR Kinetic Experiments The same general procedure was given in Chapter 2, and is given here with modifications. The kinetic experiments were run in NMR tubes containing a sealed capillary tube of deuterated benzene and CFCl3 as the internal standard. The NMR tubes were capped with natural rubber septa, and se aled with Teflon tape before any chemicals were added. Using a micro-syringe, 15 L (6.04 x 10-6 mol) of IRfSO3Na solution were added to each tube. Exact amounts of stock sa lt solutions were added to each NMR tube via micro-syringes. Equal amounts of THF-d8 were added to each tube, along with the varied amounts of the hydrogen donors. Dei onized water was added to each NMR tube so that the total volume of reaction mixture was 565 L. The samples were degassed 3 times using the freeze-pump-thaw met hod. Subsequent to the initial 19F NMR taken, the samples were irradiated for 16 hours in the RPR-204 Rayonet photochemical reactor (254 nm). 19F NMR spectra were taken ag ain, and all peaks of significance were integrated. The product ratios were obtained from the integration of the CF2H (dt, -138.3) and CF2D (m, -139.0 ppm) peaks. The conversion and yield were obtained by integration of the CFCl3 peak in the starting material and the inte grated product peaks. Tables of kinetic data and plots are given in section 3.4.7.

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85 3.4.5 Kinetic Measurements by Time-R esolved Laser Flash Photolysis The same general procedure is given in Chap ter 2, and has been described elsewhere in detail. 73, 92 The radicals, RfSO3 were generated instanta neously by 308 nm LFP of aqueous solutions of the parent iodide at ambient temperatur e. Since the product of the RfSO3 reaction with H-atoms donors, TFEO, HFIPO, and TFIPO can not be directly observed, the rate constants were determined via a competitive process using sodium 4(1-propenyl)benzoate as a ki netic probe. The transient is easily observed at 320 nm. 3.4.6 Preparation of Compound 11 See Scheme 3-6 for structures. 110 50 mL of benzyl magnesium chloride (20% w/w in THF, 0.066 mol) was placed in an equilibration funnel. Excess ethyl trifluoroa cetate (14 mL, 0.117 mol) was added to 50 mL of dry diethyl ether and cooled to -78 C under nitrogen. The Grinard reagent was added drop wise via an equalizing funnel to the stirred solution ove r a 1 hour time period. The temperature was allowed to achieve r oom temperature upon addition. The mixture was hydrolyzed with 20% HCl, a nd then saturated with brine. The mixture was extracted with 3 x 50 mL of diethyl ether, and the orga nic layer was dried over magnesium sulfate. Upon removal of the diethyl ether by roto-eva poration, benzyl triflu oromethyl ketone was distilled (BP15 = 75 C) and obtained in 60% yield for use in the next step. All spectroscopic information has been reported. 110 The ketone (7.39 g, 0.0393 mol) was added to a 100 mL rb flask along with 13 mL of absolute ethanol under nitrogen. Excess N,N-dimethyl hydrazene (12.04 mL, 0.157 mol) wa s slowly added via a syringe to the stirred reaction mixture. A reflux condenser was added to the reaction set up at this time. A catalytic amount of glacial acetic acid (.20 mL) was added via a syringe to the reaction mixture. The reaction mixture was refluxed at 85 C for 24 hours. The excess hydrazene

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86 and ethanol was removed by roto-evaporati on, and the crude product was dissolved in diethyl ether and dried with magnesium sulfat e. The diethyl ethe r was removed by rotoevaporation and the crude product was purified by distillation (BP15 = 112 C). The N,Ndimethyl hydrazone was obtaine d in 80% yield and used for the next step. All spectroscopic data ha s been reported. 110 The resulting hydrazone (7.20 g, 0.0313 mol) was added to a 3-neck 250 mL round bottom flask which was equipped with an addition funnel with nitrogen inlet. 25 mL of dry THF was charged to the flask, and cooled to -60 C. 21 mL of n-BuLi (1.6 M in hexane, 0.0334 mol) was added dropwise and resulted in a dark green solution. The solution was stirred at -60 C for an additional 3 hours. Methyl iodide (4.60 g, 0.0324 mo l) in 8 mL of THF was added dropwise to the dark green solution. The color gradually went from green to a straw color. The solution was allowed to achieve room temperature over 5 hours. The solution was hydrolyzed with ice water and saturated with brine. The orga nic phase was extracted with 4 x 80 mL of diethyl ether, and dried with magnesium su lfate. Excess ether was removed via rotoevaporation, and the crude product was dist illed under vacuum to give the alkylated hydrazone (6.50 g, 85% yield): BP15 = 118 C; 1H NMR (300 MHz, CDCl3) 1.53 (d, J = 7.3 Hz, 3H); 2.51 (s, 6H); 4.66 (q, J = 7.3 Hz, 1H); 7.0-7.6 (m, 5H); 19F NMR (CFCl3, CDCl3) -64.0 (s, 3F) The alkylated hydrazone (6.49 g, 0.0266 mol) was placed in a round bottom flask and dissolved in 90 mL of diethyl ether. 15 mL of 20% HCl was added and the reaction was stirred over night at ambient temperature. The resulting solution was saturated with brine and extracted with 4 x 50 mL of diethyl et her. Upon drying the organic layer with magnesium sulfate and removing the diethyl ether by roto-evaporati on, the crude product

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87 was distilled under reduced pressure to give the alkylated ketone (4.26 g, 79% yield): BP15 = 69-71 C; 1H NMR (300 MHz, CDCl3) 1.50 (d, J = 6.5 Hz, 3H); 4.15 (q, J = 6.5 Hz, 1H); 7.20 (s, 5H); 19F NMR (282 MHz, CDCl3) -77.9 (s, 3F) Lithium aluminum hydride (6.32 mL, 1 M in diethyl ether, 0.00632 mol) was stirred in 15 mL of dry diethyl ether under nitrogen in an ice bath. The alkylated ketone (4.26 g, 0.0211 mol) was dissolved in 10 mL of diethyl ether and added dropwise to the stirred suspension. The solution was allowed to ach ieve room temperature overnight, and was hydrolyzed with 50 mL of water. The solu tion was saturated with sodium potassium tartrate. The organic layer was extracted wi th 4 x 60 mL of diethyl ether and washed with brine and dried with ma gnesium sulfate. The diethy l ether was removed by rotoevaporation and the crude product was distil led under reduced pressure to give the alkylated alcohol as a diasteromeri c mixture 9:1 (4.18 g, 95% yield): BP10 = 90-92 C; 1H NMR (300 MHz, CDCl3) 1.43 (d, J = 6.6 Hz, 3H); 4.06 (m, 1H); 5.10 (m, 1H); 7.20 (s, 5H); 19F NMR (282 MHz, CDCl3) -70.5 (s) + -71.5 (s), 9:1 respectively Compound 11 was prepared by the usual method for preparing alkoxide sodium salts and was obtained in 80% yield: 1H NMR (300 MHz, D2O) 2.18 (m, 3H); 4.23 (m, 1H); 5.05 (m, 1H); 7.10-7.23 (m, 5H); 19F NMR (282 MHz, D2O) -68.3 (s) + -69.3 (s), 9:1 respectively

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88 Sodium Hexafluoroisopropoxide vs THF-d8y = 26.712x 0.2072 R2 = 0.9946 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 0.0750.0950.1150.1350.1550.1750.1950.2150.235 [1]/[2][H-abs]/[D-abs]3.4.7 Tables of Kinetic Data and Plots [NaO3SCF2CF2OCF2CF2I] = .0108M for all runs; all yields over 98% Table 3-6. Rate data for s odium hexafluoroisopropoxide/THF-d8 competition Entry [H-Donor] / mol L-1 [H] / [THF-d8] [ 3H]/[ 3D] 1 .107 .097 2.29 2 .134 .122 3.02 3 .161 .145 3.77 4 .187 .171 4.45 5 .214 .195 5.02 6 .241 .219 5.53 Figure 3-4. Plot of [ 3H]/[ 3D] vs. [sodium hexafluo roisopropoxide]/[THF-d8] kH/kD = Slope = 26.71 (.983) Intercept = -.207 (.161) R2 = .995

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89 THF vs Hexafluoroisopropoxide-Dy = 1.9416x + 0.0367 R2 = 0.999 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0.150.250.350.450.550.650.75 [THF]/[D][RfH]/[RfD]Table 3-7. Rate data fo r THF/sodium hexafluoroisopropoxide-D competition Entry [H] Donor, mol L-1 [THF]/[D] [ 3H]/[ 3D] 1 .120 .197 .419 2 .177 .289 .602 3 .265 .433 .861 4 .331 .542 1.11 5 .395 .646 1.28 6 .437 .714 1.42 Figure 3-5. Plot of [ 3H]/[ 3D] vs. [THF]/[sodium he xafluoroisopropoxide-D] kH/kD = Slope = 1.94 ( .032) Intercept = .0367 ( .0160) R2 = .999

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90 Trifluoroethoxide vs THF-d8y = 17.783x 0.5274 R2 = 0.9972 1 1.5 2 2.5 3 3.5 4 0.10.120.140.160.180.20.220.240.26 [H]/[D][RfH]/[RfD]Table 3-8. Rate data for s odium trifluoroethoxide/THF-d8 competition Entry [H] Donor, mol L-1 [H]/[THF-d8] [ 3H]/[ 3D] 1 .120 .110 1.42 2 .150 .138 1.92 3 .180 .165 2.39 4 .210 .189 2.92 5 .240 .218 3.29 6 .270 .247 3.87 Figure 3-6. Plot of [ 3H]/[ 3D] vs. [sodium trifl uoroethoxide]/[THF-d8] kH/kD = Slope = 17.78 ( .470) Intercept = .527 ( .087) R2 = .997

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91 HFIPO vs HFIPO-Dy = 5.8798x + 0.2427 R2 = 0.984 2 2.5 3 3.5 4 4.5 5 5.5 0.350.40.450.50.550.60.650.70.750.80.85 [H]/[D][RfH]/[RfD]Table 3-9. Rate data for sodi um hexafluoroisopropoxide/sodium hexafluoroisopropoxide-D competition Figure 3-7. Plot of [ 3H]/[ 3D] vs. [sodium hexafluo roisopropoxide]/[sodium hexafluoroisopropoxide-D] kH/kD = Slope = 5.88 ( .433) Intercept = .243 ( .267) R2 = .984 Entry [H] Donor, mol L-1[H]/[D] [ 3H]/[ 3D] 1 .109 .417 2.74 2 .136 .522 3.36 3 .163 .626 3.75 4 .177 .678 4.21 5 .204 .782 4.94

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92 Trifluoroethoxide vs HFIPO-Dy = 4.6419x 0.6392 R2 = 0.9993 0 0.5 1 1.5 2 2.5 3 0.220.320.420.520.620.720.82 [H]/[D][RfH]/[RfD]Table 3-10. Rate data for sodium trifl uoroethoxide/sodium he xafluoroisopropoxide-D competition Entry [H] Donor, mol L-1 [H]/[D] [ 3H]/[ 3D] 1 .086 .292 .700 2 .114 .389 1.19 3 .143 .486 1.60 4 .172 .584 2.10 5 .186 .633 2.29 6 .214 .730 2.74 Figure 3-8. Plot of [ 3H]/[ 3D] vs. [sodium trifl uoroethoxide]/[sodium hexafluoroisopropoxide-D] kH/kD = Slope = 4.64 (.063) Intercept = .639 (.034) R2 = .999

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93 TrifluoroisoPO vs THF-d8y = 36.96x 0.477 R2 = 0.986 0 0.5 1 1.5 2 2.5 3 0.010.020.030.040.050.060.070.080.09 [H]/[D][RfH]/[RfD]Table 3-11. Rate data for sodi um trifluoroisopropoxide/THF-d8 competition Entry [H] Donor, mol L-1 [H]/[D] [ 3H]/[ 3D] 1 .038 .017 .264 2 .077 .034 .780 3 .100 .045 1.10 4 .115 .051 1.38 5 .154 .069 1.92 6 .192 .085 2.83 Figure 3-9. Plot of [ 3H]/[ 3D] vs. [sodium trifl uoroisopropoxide]/[THF-d8] kH/kD = Slope = 36.96 (.46) Intercept = .477 (.135) R2 = .986

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94 HFIPOH vs MeOH-d4y = 9.4526x 0.594 R2 = 0.9972 0 0.5 1 1.5 2 2.5 3 3.5 0.10.150.20.250.30.350.4 [H]/[D][RfH]/[RfD]Table 3-12. Rate data for hexafluoroisopropanol/MeOD-d4 competition Entry [H] Donor, mol l-1 [H]/[ MeOD-d4] [ 3H]/[ 3D] 1 .656 .145 .801 2 .850 .188 1.19 3 1.06 .234 1.62 4 1.23 .273 1.91 5 1.46 .323 2.46 6 1.62 .362 2.87 Figure 3-10. Plot of [ 3H]/[ 3D] vs. [hexafluoroi sopropanol]/[MeOH-d4] kH/kD = Slope = 9.45 (.249) Intercept = .594 (.066) R2 = .997

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95 Cl3CCH(OH)2 (1)/THF-d8 (2)y = 0.1988x + 0.179 R2 = 0.9703 1.1 1.3 1.5 1.7 1.9 2.1 2.3 66.577.588.599.510 [1] / [2][H-abs]/[D-abs]Table 3-13. Rate data for Cl3CCH(OH)2/THF-d8 competition Entry [H-Donor], mol L-1 [Cl3CCH(OH)2]/ [THF-d8] [ 3H]/[ 3D] 1 2.83 6.35 1.42 2 3.36 7.57 1.74 3 3.54 8.10 1.79 4 3.89 8.70 1.85 5 4.25 9.56 2.10 Figure 3-11. Plot of [ 3H]/[ 3D] vs. [Cl3CCH(OH)2]/[THF-d8] kH/kD = Slope = .198 (.020) Intercept = .179 (.163) R2 = .970

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96 Cl3CCH(OH)ONa (1)/THF-d8 (2)y = 37.357x 0.1239 R2 = 0.9868 1 1.5 2 2.5 3 3.5 4 4.5 0.030.040.050.060.070.080.090.10.110.12 [1] / [2][H-abs]/[D-abs]Table 3-14. Rate data for Cl3CCH(OH)ONa/THF-d8 competition Entry [Cl3CCH(OH)ONa] mol L-1 [Cl3CCH(OH)ONa]/ [THF-d8] [ 3H]/[ 3D] 1 .0651 .0373 1.24 2 .0977 .0562 1.88 3 .114 .0657 2.35 4 .136 .0780 2.94 5 .163 .0936 3.47 6 .190 .109 3.80 Figure 3-12. Plot of [ 3H]/[ 3D] vs. [Cl3CCH(OH)ONa]/[THF-d8] kH/kD = Slope = 37.36 (.16) Intercept = -.124 (.166) R2 = .987

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97 F3CCH(OH)2 (1)/THF-d8 (2)y = 0.0304x + 0.2653 R2 = 0.9904 0.46 0.51 0.56 0.61 0.66 0.71 67891011121314 [1] / [2][H-abs]/[D-abs]Table 3-15. Rate data for F3CCH(OH)2/THF-d8 competition Entry [F3CCH(OH)2] (mol L-1) [F3CCH(OH)2]/ [THF-d8] [ 3H]/[ 3D] 1 2.45 7.21 .479 2 3.33 9.86 .570 3 3.56 10.54 .587 4 4.43 13.18 .657 5 4.65 11.78 .630 Figure 3-13. Plot of [ 3H]/[ 3D] vs. [F3CCH(OH)2]/[THF-d8] kH/kD = Slope = .0304 (.0017) Intercept = .265 (.018) R2 = .990

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98 F3CCH(OH)ONa (1)/THF-d8 (2) y = 40.72x 0.1676 R2 = 0.9949 1.5 2 2.5 3 3.5 4 0.040.050.060.070.080.090.1 [1] / [2][H-abs]/[D-abs]Table 3-16. Rate data for F3CCH(OH)ONa/THF-d8 competition Entry [F3CCH(OH)ONa]/ (mol L-1) [F3CCH(OH)ONa]/ [THF-d8] [ 3H]/[ 3D] 1 .0967 .0486 1.78 2 .107 .0539 2.02 3 .123 .0624 2.35 4 .134 .0679 2.69 5 .188 .0950 3.67 Figure 3-14. Plot of [ 3H]/[ 3D] vs. [F3CCH(OH)ONa]/[THF-d8] kH/kD = Slope = 40.72 (.69) Intercept = -.168 (.114) R2 = .995

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99 Laser Flash Photolysis Data Table 3-17. Rate data for H-atom abstra ction from sodium trifluoroethoxide by RfSO3Na in water [H-donor], M kex/s-1 [ 2 ] a M kex kST [ 2 ]/s-1 Experiment 1 0.000 7.97E+04 2.17E-03 4.26E+03 0.154 9.61E+04 2.17E-03 1.22E+04 0.232 1.10E+05 2.17E-03 2.58E+04 0.347 1.13E+05 2.17E-03 2.95E+04 0.521 1.30E+05 2.17E-03 4.57E+04 0.729 1.61E+05 2.17E-03 7.67E+04 1.020 1.84E+05 2.17E-03 1.00E+05 1.430 2.46E+05 2.17E-03 1.62E+05 a. 2 is the spectroscopic probe, 4-(1-p ropenyl)benzoate; b. Plot of kex vs. [ 2 ] Slope b = 1.13+05 R2 = 0.9899 std err slope = 4.6E+03 confidence interval = 8.6E+03 kH(TFEO) = (11.3 0.1) x 104 M-1s-1

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100 Table 3-17. Continued: [H-donor], M kex/s-1 [ 2 ]a, M kex kST [ 2 ]/s-1 0.000 7.99E+04 2.00E-03 2.88E+03 0.159 9.79E+04 2.00E-03 2.07E+04 0.238 1.16E+05 2.00E-03 3.92E+04 0.357 1.32E+05 2.00E-03 5.50E+04 0.500 1.39E+05 2.00E-03 6.17E+04 0.700 1.69E+05 2.00E-03 9.13E+04 0.980 1.79E+05 2.00E-03 1.02E+05 1.370 2.10E+05 2.00E-03 1.33E+05 1.920 2.88E+05 2.00E-03 2.11E+05 a. 2 is the spectroscopic probe, 4-(1-p ropenyl)benzoate; b. Plot of kex vs. [ 2 ] Slope b = 1.00E+05 R2 = 0.9804 std err slope = 5.4E+03 confidence interval = 9.8E+03 kH(TFEO) = (10.0 0.1) x 104 M-1s-1

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101 Table 3-18. Rate data for H-atom abstrac tion from sodium trifluoroisopropoxide by RfSO3Na in water [H-donor] / M kex / s-1 [ 2 ]a / M kex kST [ 2 ] / s-1 Entry 1 0.000 8.17E+04 1.97E-03 5.75E+03 0.105 1.06E+05 1.59E-03 4.44E+04 0.211 1.46E+05 1.97E-03 7.01E+04 0.317 2.26E+05 1.97E-03 1.50E+05 0.444 3.51E+05 1.97E-03 2.75E+05 0.666 4.14E+05 1.97E-03 3.38E+05 0.933 5.40E+05 1.97E-03 4.64E+05 1.306 7.00E+05 1.97E-03 6.24E+05 a. 2 is the spectroscopic probe, 4-(1-p ropenyl)benzoate; b. Plot of kex vs. [ 2 ] Slope b = 4.92E+05 R2 = 0.9932 std err slope = 1.5E+04 confidence interval = 2.8E+04 k = (49.2 2.8) x 104 M-1s-1

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102 CHAPTER 4 LARGE PRIMARY KINETIC ISOTOPE EF FECTS IN THE ABSTRACTION OF HYDROGEN FROM ORGANIC COMPOUNDS BY A FLUOR INATED RADICAL IN WATER 4.1 Introduction Chapter two and three serves as a test ament to the broad study involving the determination of rate constants of hydrogen at om abstraction from organic substrates by the fluorinated radical, O3SCF2CF2OCF2CF2, in water. The rate constants for abstraction of hydrogen from isopropanol in BT B and water exemplify the very large rate constants of such processes, and the modest rate enhancing effect of the polar solvent water (Figure 4-1). Figure 4-1. Rate constants for H-abstra ction from isopropanol in BTB and water These absolute rate constants were determined by competition studies in which the fluorinated radical (O3SCF2CF2OCF2CF2) abstracted hydrogen from the substrate in competition with abstraction of a deuterium fr om a standard, carefully chosen for which the rate constant for D-abstraction ha d been determined (Figure 4-2). O3SCF2CF2OCF2CF2 C H OH 25 C, solventRf RfH C OH Rf Solvent kH CF3CF2CF2CF2 BTB H2O 1.6 x 104 M-1 s-14.8 x 104 M-1 s-1

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103 The requirements for the deuterium transfer agent were stringent, requiring the agent to participate in creating a clean radica l chain process that gave high conversions and excellent mass balance. Indeed, all compe tition studies necessitate high yields of the two reduced products with virt ually no observable side produc ts. The rate constant for D-abstraction must also be of a magnitude that allowed a vi able competition between Htransfer from a plethora of H-atom donors and D-transfer to be observed. t -BuMe2SiD, with a measured kD of 1.5 (.3) x 105 M-1 s-1, 63 and THF-d8 with a measured kD of 4.2 (.2) x 103 M-1 s-1 (Chapter 2), fulfilled these requirements admirably for the competition studies in BTB and water, respecti vely, and they were therefore used as the D-transfer agents in these respective studies. Figure 4-2. Typical competition experiment These rate constants can be compared with their kH values for the respective nondeuterated compounds, 4.9 x 105 M-1 s-1 for t -BuMe2SiH (in BTB)63 and 3.3 x 104 M-1 s-1 for THF (in H2O), which allowed the isotope effect (kH/kD) for H versus D abstraction from these two compounds to be calculated (Equation 4-1). The cal culated values of 3.3 and 7.9 for t -BuMe2SiH and THF, respectively, repr esent nothing extraordinary. A similar isotope effect (kH/kD = 3.1) was observed for another silane, Et3SiH, in another O3SRfI Radical Precursor h H2O O3SRf H-Donor kHkDTHF-d8O3SRfH O3SRfD exclusively f r o m H-Dono r exclusively from THF-d81 3H3D4

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104 non-polar solvent, 1,1,2 -trichloro-1,2,2-trif luoroethane (F113), 111 whereas the isotope effect for THF versus THF-d8 in BTB was 7.0 at 25 C. 63 Equation 4-1. Calculation of isotope effects for t -BuMe2SiH and THF However, particularly in the water study, many other prospective D-transfer agents were tested for possible use, including CD3OD and CD3OCD3. During the course of such testing, both the H-transfer and the D-transfer rate constant s were determined for these compounds, and the results were surprising in that unusually large is otope effects (kH/kD = 11.4 and 17.0, respectively) were obser ved for the progressively slower Htransfer agents. Of course, these two observed isotope effect values, as well as the earlier mentioned value for THF, derive from a combination of primary and secondary deuterium isotope effects, but it will be seen that the actual primary isotope effects, once corrected for the small secondary eff ect contribution, remain quite large. These observations led to a more systematic examination of the primary and secondary kinetic isotope effects that derive from hydrogen transfer to the O3SCF2CF2OCF2CF2 ( 4 ) radical. 4.2 Results The observed kinetic isotope effects (kH/kD, a combination of primary and secondary isotope effects), were obtained vi a direct competition experiments involving the photolysis of O3SCF2CF2OCF2CF2I ( 1 ) in the presence of mixt ures of the respective protiated and deuterated substr ates, varying relative concentr ations in order to establish k H(t-BuMe2Si H ) kD(t-BuMe2SiD) = 4.9 x 105 M-1 s-11.5 x 105 M-1 s-1 = 3.3 kH(THF) kD(THF-d8) = 3.3 x 104 M-1 s-14.2 x 103 M-1 s-1 = 7.9

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105 the linearity (pseudo first or der) of the concentration de pendence of the substrates towards proton/deuterium transfer. The co mpetition methodology was described in detail in Chapter 2, and the only modification is th at for the present case the deuterium donor is the deuterated analog of the protiated species, not THF-d8. The conversions were 100%, with the mass balance of products always being above 95%. The linear relationship between the ratio of RfH/RfD products and the ratio of pro tiated and deuterated reactants defined the value of the isotope effect (kH/kD). The derivation of both relative and absolute rate constants from such data has been discussed in detail in Chapter 2. A typical competition and the resulting plot are given in Figure 4-3, and Figure 4-4. Figure 4-3. Competition between acetone and deuterated acetone The kinetic isotope effect observed for acetone (17) is much larger than the semiclassical maximum for isotope effects, 7 at 25 C. Although acetone has a very large kinetic isotope effect, generally isotope effects are expected to be from 1-7. The C-D bond sits lower in the potential energy we ll, thus requires more energy to break than does the C-H O3SCF2CF2OCF2CF2 H3C CH3 O D3C CD3 O kHkDO3SCF2CF2OCF2CF2H O3SCF2CF2OCF2CF2D 3H3DkH/kD = 17.0

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106 Acetone vs. Acetone-d6y = 17.028x 0.0074 R2 = 0.9975 0 1 2 3 4 5 6 7 8 00.050.10.150.20.250.30.350.40.45 [(CH3)2CO]/[(CD3)2CO][3H]/[3D]bond. Therefore, the radical will abstract th e hydrogen atom faster than the deuterium atom. Figure 4-4. Plot of the kinetic data for acetone The observed kinetic isotope effects given in the 3rd column of Table 4-1 in all cases except the first derive from a combination of primary and secondary kinetic deuterium isotope effects, the latter being either or in nature (or in the case of CD3CD2OH, both and -). The definitions of these secondar y isotope effects will be discussed in great detail in section 4.2.1. The absolute values of kH rate constants were determined previously and reported in Chapters 2 and 3. Therefore, knowledge of the kH/kD values in Table 4-1 allows determination of the values for kD for the given deuterated compound.

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107 Table 4-1. Observed kinetic isotope effects for several organic compounds H-Donor D-Donor kH/kD a kH/104 M-1 s-1 b kD/104 M-1 s-1 (CF3)2CHONa+ (CF3)2CDONa+ 5.9 (.4) 11 () 1.86 (.6) Isopropanol (CD3)2CDOH 5.8 (.1) 4.8 (.4) 0.83 (.25) (CD3)2CHOH THF-d8 8.9 (.3) 3.7 (.1) 0.42 (.13) THF THF-d8 7.9 (.4) 3.3 (.0) 0.42 (.13) Ethanol CD3CD2OH 8.8 (.2) 1.2 (.4) 0.14 (.04) Ethanol CH3CD2OH 8.11 (.12) 1.2 (.4) 0.15 (.04) CH3CHDOH 7.39 (.04) Methanol CD3OH 11.4 (.4) 0.18 (.05) 0.016 (.005) CHD2OH 4.83 (.02) Acetone Acetone-d6 17.0 (.4) 0.006 (.002) 0.00035 Acetic acid CD3CO2H 22.2 (.7) 0.002(.0006) 0.00009 a. Errors in this column are standard deviat ions; b. LFP derived absolute rate constants 4.2.1 Secondary Deuteriu m Isotope Effects Because of the multiple deuterium s ubstitution that is present in THF-d8, CD3CD2OH, CH3CD2OH, CD3OH, acetone-d6, and CD3CO2H, it is necessary to have some measure of expected and -secondary deuterium isotope effects in order to be able to calculate the actual primary isotope e ffects for these substrates. For example, in the case of CD3CD2OH, when the rate constant, kD, for -deuterium is measured, the remaining -deuterium and the three -deuteriums give rise to secondary isotope effects that lower the rate constant compared to what it would have been had only hydrogens remained in the radical product, as depicted in Figure 4-5. Th e overall effect on the

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108 observed primary (deuterium being abstracted) isotope effect is ther efore, a higher value for the primary kinetic isotope effect because kD in the ratio is smaller than it should be. Figure 4-5. Transition state for D-abstra ction from pentadeuteroethanol showing and -secondary deuteriums The -secondary isotope effects derive from hyperconjugative effects which are quite small. The -deuterium, however, is attached directly to the carbon bearing the deuterium being abstracted, and causes more re sistance to changes in hybridization in the transition state than a hydrogen atom would cause. Since the -deuterium is attached directly to the reaction site, slowing effect on the deuterium abstraction is greater than those observed for -secondary isotope effects. In order to determine the values of the secondary isotope effects, four additional competition experiments were carried out. These were (i) the intermolecular competition between (CD3)2CHOH and THF-d8, (ii) the intermolecular competition between CH3CD2OH and CH3CH2OH, and intramolecular competitions using (iii) CH3CHDOH and (iv) CHD2OH. The data for these experiments are contained in Table 4-1 and Table 4-2. The first two experiments allowed independent determinations of the -secondary deuterium isotope effect, the values of which are calculated to be 1.28 and 1.088, for D D D D D OH F RfSO3 F

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109 isopropanol and ethanol respec tively, or 1.04 and 1.03 per deut erium in each case (using the sixth root and cube root of the ov erall isotope effects respectively). Table 4-2. Data used to calculate secondary deuterium isotope effects H-Effect D-Effect kH(Effect) kD(Effect) kH/kD (secondary) kH/kD (per D) (CH3)2CHOH (CD3)2CHOH4.8 a 3.74 a 1.28 1.04 c ( ) CH3CD2OH CD3CD2OH 0.148 b 0.136 b 1.088 1.03 d ( ) CH3CHDOH kH/kD = 7.39 1.07 1.07 e ( ) CHD2OH kH/kD = 4.83 1.10 1.05 f ( ) a. competition versus THF-d8 as the deuterium donor; b. competition versus CH3CH2OH as the hydrogen donor; c. obtained by taking the 6 of 1.28; d. obtained by taking the 3 of 1.088; e. see Equation 4-2 for deta ils; f. see Equation 4-3 for details The results from the intramolecular competition experiments using CH3CHDOH and CHD2OH allowed two determinations of the value of the -secondary deuterium isotope effect. The isotope effect for the CH3CHDOH system can be calculated from the raw 3H/3D integral according to Equation 4-2. Equation 4-2. Calculation of the -secondary deuterium isotope effect for CH3CHDOH [ 3H] integr a l [ 3D] integral = kH(EtO H ) x kD/kH(-seco n d a r y ) kD(CH3CD2OH) x kH/kD( -secondary) 7.39 = 12 x [kD/kH( -secondary)]2 1.5 kH/kD = 1.05

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110 However, a 500 MHz 1H NMR spectrum of the synthesized CH3CHDOH indicated that it contained a 1% diethyl ether contaminant (4% integral of its CH2 groups versus 100% integral for the CHD of the mono-deuter oethanol) as shown in the Appendix. This small amount of contaminant will have a small, but not negligible impact upon the 3H/3D integral ratio, which when taken into account yields a corrected value of 1.07 for the secondary deuterium isotope effect for the et hanol system. The details of the calculation of the correction can be found in the experimental section. The value of the isotope effect in the meth anol system can likewise be calculated as shown in Equation 4-3. Equation 4-3. Calculation of the -secondary deuterium isotope effect for CHD2OH Although the absolute rate constants in Table 4-1 do have some error associated with the LFP competition experiments, the data obtained in the competition studies have standard deviations generally in the 3-4% range, whic h allows the values of the secondary isotope effects to be credible. The relatively small -effects are consistent with the limited data that have been previously repor ted for radical forming reactions. 112, 113 For example, in studies of the deazetation of deuterium la beled azo compounds, Seltzer and coworkers found that -secondary deuterium isotope effects, which derive from hyperconjugative interaction of the isotopically labeled site with the incipient -radical site, were generally [ 3H] integral [ 3D] integral = 1/3 x kH(CH3OH) x kD/kH( -secondary)2 2/3 x kD(CD3OH) x kH/kD( -secondary) 4.83 = 0.33 x 0.18 x [kD/kH( -secondary)]3 0.667 x 0.016 kH/kD = 1.05

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111 much smaller for radical forming reactions than for carbocation forming reactions (Figure 4-6). Ph C Y 3 X N N C Y 3 X Ph 105 C ethylbenzene Ph CY3 X 2 + N2-isotope effect: X = D, Y = H, kH/kD = 1.13 per D -isotope effect: X = H, Y = D, kH/kD = 1.02 per D Figure 4-6. Secondary deuterium isotope effects for a radical forming reaction In contrast, -secondary deuterium isotope effects which can be understood as deriving from a change in hybridization at the radica l forming carbon atom, have been found to be of similar magnitude to those derivi ng from carbocation forming reactions. 114 Thus the average of the two -secondary deuterium isotope effects observed, kH/kD = 1.06, is somewhat smaller than might have been expe cted based on the limited data available in literature for radical forming reactions. Ho wever, the faster, exothermic hydrogen atom abstractions of the current study should have much earlier transition states than the endothermic dissociative reactions studied by Se ltzer, a fact consistent with the smaller secondary deuterium isotope effect of the current study. 4.2.2 Primary Deuterium Isotope Effects With both the and -secondary isotope effects now in hand, it becomes possible to convert the observed primary isotope effect s to pure primary deut erium isotope effects for each substrate. For isopropanol, ethanol, and methanol the specific values of the secondary isotope effects that were determin ed have been used, whereas for the THF, acetone and acetic acid calculations, th e per deuterium value of 1.06 for the and 1.035

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112 for the -secondary isotope effects were used fo r the correction. The calculated, true primary isotope effects are given in Table 4-3. Table 4-3. Corrected primary isotope effects Substrate kH/kD (uncorr.) Corrections kH/kD (primary) (CF3)2CHONa+ 5.9 none 5.9 Isopropanol 5.8 6 (1.28) a 4.5 THF 7.9 1 2 (1.14) 6.8 Ethanol 8.8 1 3 (1.16) a 7.6 Methanol 11.4 2 (1.10) a 10.3 Acetone 17 2 (1.12) 15.9 Acetic acid 22.2 2 (1.12) 21.1 a. correction values determined directly 4.3 Discussion The values of the isotope effects for the last three substrates are considerably larger than what are generally consid ered to be the theoretical limits for semiclassical H/D primary isotope effects. It can be seen th at the values exhibit a correlation with the absolute rate constants for H-transfer, which vary over a considerable range, with acetic acid being about 3000 times less reactive than is opropanol. From a transition state theory point of view, the observed correlation can be explained by the fact that the slower Htransfer donors have a later, though still relatively early, transition state. The later transition states require mo re bond breaking, and therefore, the radical becomes more selective for the hydrogen over the deuteriu m atom. The absolute rate constants themselves correlate with C-H BD Es of the respective substrates.

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113 The very large isotope effects for the last three entries in Table 4-3 appear to be real. The reactions are clean, and good linea r correlations with concentrations are observed. One possible trivial explanation for the data might have been that H-transfer from water could have become increasingly competitive with H-transfer from the less reactive substrates. However, the competition experiments for acetone were run in both H2O and D2O, with the observed kH/kD in D2O being 18.5 0.7, which indicates that Htransfer from the solvent water can not be co mpetitive with H-transfer from the substrates under the conditions of this study. Kinetic isotope effects (kH/kD) derive from a difference in the zero point energies of hydrogen and deuterium substituted compounds. For primary kinetic isotope effects, the bond of the isotopically labeled atom is being broken in the transition state of the rate determining step. C-H bonds have characterist ic vibrations which are a means of energy storage for a molecule. This vibrational en ergy is known as the zero point energy. Since the vibrational energy is dependant on the mass of the vibrating atom, C-D bonds contribute less to the zero point energy due to the greater mass of the deuterium atom lowering the vibrational frequency of the bond. C-D bonds are lower in energy than the C-H bonds, and effectively lower the zero po int energy. Cleavage of a hydrogen or deuterium bond results in a vibrational degree of freedom being converted to a translational degree of freedom in the transi tion state. Therefore, the energy difference between the hydrogen and deuteriu m vibrations disappears in th e transition state. As a result, the transition state for reactions involving protiated an d deuterated molecules have the same energy. The activation energy for the bond breaking of a C-D bond is greater, and results in the reaction bei ng kinetically slower. Primary kinetic isotope effects vary

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114 considerably depending on the natu re of the transition state. However, the semiclassical limit occurs when the hydrogen atom being transferred is bound equally between two other atoms in the transition state. For primary kinetic isotope effects (kH/kD) the maximum value is about 7 at room temperature. Tunneling must be considered as a possi ble contributing factor to such large isotope effects that are certai nly outside of the generally ac cepted semiclassical limits for hydrogen transfer isotope effects, where one assumes that the zero point energy difference associated with carbon-hydrogen stre tching in the substrate is completely lost in the transition state. 115 Isotope effects moderately la rger than the ~7.0 limit at 25 C can be accommodated by allowing weakening of bending modes, but when such large values as those found in Table 4-3 are obser ved, one is almost compelled to invoke tunneling. 115 Therefore, to probe the possibility of tunneling, a temperature profile was carried out for the acetone competition. The te mperature range for such a study is limited in the present case due to the fact that the competition experiments are performed in water. The values determined for kH/kD at 24, 56, and 80 C were 16.6 (.7), 12.6 (.1), and 10.2 (.5), respectively (Figure 4-7). A linear corre lation is apparent in the Arrhenius plot between ln(kH/kD) versus 1/T, with Ea(D) Ea(H) = 1.8 kcal mol-1 and AH/AD = 0.80. The Kreevoy group has indicated, 116 there is probably no unambiguous way to demonstrate tunneling for reactions carried out around 300 K. 117 However, he and others contend that, even in this te mperature range, values of Ea(D) Ea(H) > 1.20 kcal mol-1 will generally indicate tunne ling, as will values of AH/AD < 1.0 for hydrogen transfer between massive, polyatomic donors and acceptors. 115, 116

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115 Figure 4-7. Temperature profile for acetone, ln(kH/kD) vs. 1/T The Arrhenius data must be considered suspect because of the small temperature range and the limited data points in the plot. Nevertheless, the data are consistent with the criteria for the involvement of tunneling in the H-transfer process. Also prudent to our study, the Truhlar group have analyzed kinetic data for the reaction of CF3 with CD3H via computational methods to determin e the kinetic isotope effect for this reaction,118 and they report that tunneling must be included in the calculation in order to attain agreement with the experimental data. 119 Also relevant to the tunneling studies, Roberto-Neto and Machado have analyzed kine tic isotope effect data for the reaction of Cl with ethane; 120 the Michelsen 121 and Hewitt 122 groups have similarly analyzed such data for the reaction of Cl with methan e, and the Osman group have examined the reaction of HO with isopropanol, 123 all concluding that tunneling effects make a significant contribution to th e H-transfer rate constants in these reactions. ln k vs. 1/T y = 902.16(+40.91)x 0.2253 R2 = 0.9979 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 0.00280.00290.0030.00310.00320.00330.0034 1/Tln k

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116 Carbon-hydrogen abstractions by alkyl radicals, and even more so by perfluoroalkyl radicals, should i nvolve relatively sterically hinder ed transition states. It is recognized that such sterically constrained transition states for hydrogen abstraction can lead to a steep rise in potential energy upon cl ose approach of the reactants to each other, resulting in a high and thin potential barrier that can lead to large tunneling contributions. 115, 124, 125 Taking all of this into account, in th e absence of any plausible alternative explanation, it is concluded th at tunneling is probably a significant factor in producing the large kinetic isotope effects observed for the C-H abstraction reactions with O3SCF2CF2OCF2CF2. 4.4 Conclusion Through the competition studies employed in studying hydrogen atom abstraction rate constants, large primary isotope effects have been discovered. These large isotope effects appear to be accurate values based on many experiments designed to verify the observed isotope effects. The contribution of and -secondary deuterium isotope effects for the reaction of O3SCF2CF2OCF2CF2 with various organic hydrogen donors has been determined. The secondary isotope ef fects were used to adjust the pure primary kinetic isotope effects, and led to the determ ination that the large kinetic isotope effects are real. The only explanation for the larg e isotope effects is the probability that tunneling contributes a significant amount in pr oducing the large, unusual kinetic isotope effects observed. 4.5 Experimental All deuterated compounds were purchased in >98% purity from CIL and Isotech, Inc, except for known compound CH3CHDOH which was synthesized by reduction of

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117 acetaldehyde by LiAlD4. NMR spectra and kinetic 19F NMR measurements were performed at 282 MHz using a Vari an VXR-300 spectrometer. All 1H NMR spectra were performed at 300 MHz on the same instru ment. All chemical shifts are reported downfield in ppm from the internal standards, CFCl3 and TMS, for fluorine and proton NMR, respectively. 4.5.1 General Procedure for Competition Kinetic Studies The same general procedure was given in Chapter 2, and is given here with modifications. The kinetic experiments were run in NMR tubes containing a sealed capillary tube of deuterated benzene and CFCl3 as the internal standard. The NMR tubes were capped with natural rubber septa, and se aled with Teflon tape before any chemicals were added. Using a micro-syringe, 15 L (6.04 x 10-6 mol) of IRfSO3Na solution were added to each tube. Exact amounts of protia ted and deuterated s ubstrates were added with syringes and weighed on a balance. Deionized water was added to each NMR tube so that the total volume of reaction mixture was 565 L. The samples were degassed 3 times using the freeze-pump-thaw met hod. Subsequent to the initial 19F NMR taken, the samples were irradiated for 16 hours in the RPR-204 Rayonet photochemical reactor. 19F NMR spectra were taken again, and all pe aks of significance were integrated. The product ratios were obtained from the integration of the CF2H (dt, -138.3) and CF2D (m, 139.0 ppm) peaks. The conversion and yield were obtained by integration of the CFCl3 peak in the starting material and the integrated product peaks. Tables of kinetic data and plots are given in section 4.5.6. 4.5.2 Correction for the Diethyl Ether Impurity in CH 3 CHDOH The CH3CHDOH was prepared and analyzed by 1H NMR. No undeuterated ethanol could be observed, but a 1% impurity of diethyl ethe r was detected (4% integral

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118 for its CH2 groups versus the 100% due to the CHD group of CH3CHDOH (see appendix). The small impact of this impurity on the measured 3H/3D ratio was corrected for in the calculation of the -secondary isotope effect (see be low for correction details). The CHD2OH was purchased from CIL. a. although the rate constant for diethyl ether in water was not measured, it is assumed that it's per hydrogen rate constant would be approximately equal to that of ethanol. This assumption is based upon a comparison of the rate constants of CH3OCH2CH2OCH3 versus HOCH2CH2OH in water (5.5 and 5.4 x 103 M-1s-1, respectively. Thus a value of 12 x 103 M-1s-1 was used in correcting the isotope effect for the 1% ether content. 4.5.3 Procedure for Measurement of th e Intramolecular Isotope Effects For both CH3CHDOH and CHD2OH, two representative kine tic studies were run in pyrex NMR tubes containing a se aled capillary tube (CFCl3, C6D6) as the internal standard, capped with rubber se pta, and wrapped with Teflon tape before any chemicals were added. In the typical case for CH3CHDOH, the IRfSO3 in water was used as a stock solution (17.8% by weight) and added to the NMR tubes with a micro-syringe. Then, 80 L of monodeuteroethanol (14.3 x 10-4 mol) was added to each tube. The samples were then degassed by thre e freeze-pump-thaw cycles. After 19F NMR spectra Correcting for 1% Et2O impurity in CH3CHDOH: a(CF2H integral) (CF2D integral) = 0.962 x kH(EtOH) x kD/ kH( -secondary) + 0.0385 x kH(Et2O) 0.962 x kD(CH3CD2OH) x kH/ kD( -secondary) 7.39 = 0.962 x 12 x [ kD/ kH( -secondary)]2 + 0.0385 x 12 x kD/ kH( -secondary) 1.42and kH/ kD = 1.07

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119 of the samples were taken, the samples were irradiated using a RPR-204 Rayonet photochemical reactor. The 19F NMR spectra for each sample were taken again after 24 hours. The product ratios were obtai ned by careful integration of the 3H and 3D signals, with multiple integrations being carried out for each. The conversion and yield were calculated against the internal st andard, as described previously. For CH3CHDOH, the average of the raw 3H/3D ratios was 7.39 (.04). For CHD2OH, the average of the raw 3H/3D ratios was 4.83 (.02). 4.5.4 Preparation of CH 3 CHDOH 5 mL of lithium aluminum deuteride (1.0 M, 0.005 mol) was stirred in 15 mL of anhydrous diethyl ether under N2 and at 0 C. 0.0572 g of acetaldehyde (0.0013 mol) in 10 mL of anhydrous diethyl et her was added dropwise via an equalizing funnel to the stirred suspension. The solution was allowed to achieve room temperature over 3 hours. The diethyl ether was remove d by vacuum pump leaving only the salt complex. Excess 1-dodecanol was added to the salt and slowly heated to 140 C, at which time, monodeuteroethanol 126 (see appendix for spectra) distille d out and was obtained (0.058 g, 94%): 1H NMR (500 MHz, D2O) 1.13 (d, J = 7.0 Hz, 3H), 3.57 (m, 1H). 4.5.5 General Procedure for the Acetone Arrhenius Data The same general procedure as was used before was used for the competition between acetone and acetone-d6. The kinetic experiments were run in NMR tubes containing a sealed capillary tube of C6D6 and CFCl3 as the internal standard. The NMR tubes were capped with natura l rubber septa, and sealed with Teflon tape before any chemicals were added. Using a micro-syringe, 15 L (6.04 E-6 moles) of IRfSO3Na solution (4.0 E-1 M) were added to each tube. 100 L (.087g, 1.4 E-3 moles) of acetone-

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120 d6 was added to each tube, along with varying amounts (10-40 L) of acetone. Deionized water was added to each NMR tube so that the total volume of reaction mixture was 565 L. The samples were degassed 3 ti mes using the freeze-pump-thaw method. Subsequent to the initial 19F NMR spectra taken, the samples were irradiated for 16 hours in the RPR-204 Rayonet photochemical reactor. When heating was necessary for the Arrhenius data, the NMR tubes were submerge d in a hot oil bath at the appropriate temperatures during the irradiation. 19F NMR spectra were again taken, and all peaks of significance were integrated. The product ra tios were obtained from the integration of the CF2H (d, .3 ppm) and CF2D (s, -139.0 ppm) peaks. The conversion and yield were obtained by integration of the CFCl3 peak in the starting material and the integration of the product peaks. See section 4.5.6 for kinetic tables and plots.

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121 4.5.6 Tables of Kinetic Data and Plots NaSO3RfI = 0.0107 M for all experiments Table 4-4. Arrhenius data for acetone at 24 C Figure 4-8. Plot of Arrhen ius data for acetone at 24 C [acetone]/[acetone-d6] [ 3H]/[ 3D] Yield (%) 0.113 1.88 98 0.16 2.67 99 0.219 3.53 100 0.27 4.33 100 0.322 5.44 100 Acetone vs. Acetone-d6 @ 24C y = 16.615(+.68)x 0.0322 R2 = 0.9949 0 1 2 3 4 5 6 00.050.10.150.20.250.30.35 [acetone]/[acetone-d6][RfH]/[RfD]

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122 Table 4-5. Arrhenius data for acetone at 56 C Figure 4-9. Plot of Arrhen ius data for acetone at 56 C [acetone]/[acetone-d6] [ 3H]/[ 3D] Yield (%) 0.116 1.62 100 0.16 2.14 100 0.212 2.76 98 0.254 3.34 100 0.306 3.95 98 0.412 5.33 100 Acetone vs. Acetone-d6 @ 56Cy = 12.556(+.13) x + 0.1346 R2 = 0.9996 0 1 2 3 4 5 6 00.050.10.150.20.250.30.350.40.45 [acetone]/[acetone-d6][RfH]/[RfD]

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123 Table 4-6. Arrhenius data for acetone at 80 C Figure 4-10. Plot of Arrhen ius data for acetone at 80 C [acetone]/[acetone-d6] [ 3H]/[ 3D] Yield (%) 0.162 2.01 99 0.217 2.39 98 0.262 2.89 100 0.311 3.53 99 0.408 4.43 100 Acetone vs. Acetone-d6 @ 80C y = 10.178(+.50)x + 0.2815 R2 = 0.9927 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 00.050.10.150.20.250.30.350.40.45 [acetone]/[acetone-d6][RfH]/[RfD]

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124 Table 4-7. Rate data for CH3OH/CD3OD competition [IRfSO3Na] (mol L-1) [CD3OD] (mol L-1) [CH3OH]/ [CD3OD] [ 3H]/[ 3D] a 0.011 4.41 0.103 1.45 0.011 4.39 0.209 2.65 0.011 4.44 0.306 4.01 0.011 4.44 0.456 5.90 0.011 4.42 0.606 7.57 0.011 4.41 0.801 9.26 a. all yields over 98% Figure 4-11. Plot of [ 3H]/[ 3D] vs. [CH3OH]/[CD3OD] kH/kD(CD3OD) = Slope = 11.4 ( 0.4) Intercept = 0.413 ( 0.215) R2 = 0.994 CH3OH vs CD3OD y = 11.431x + 0.4131 R2 = 0.9938 0 2 4 6 8 10 12 00.20.40.60.81 [CH3OH]/[CD3OD][RfH]/[RfD]

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125 Table 4-8. Rate data for THF/THF-d8 competition [IRfSO3Na] (mol L-1) [THF-d8] (mol L-1) [THF]/ [THF-d8] [ 3H]/[ 3D] 0.013 1.29 0.204 1.67 0.013 1.28 0.415 3.47 0.013 1.28 0.605 5.03 0.013 1.28 0.809 6.68 0.013 1.30 0.990 7.40 0.013 1.28 1.22 9.99 Figure 4-12. Plot of [ 3H]/[ 3D] vs. [THF]/[THF-d8] kH/ kD THF-d8 = Slope = 7.87 ( 0.38) Intercept = 0.140 ( 0.296) R2 = 0.991 THF vs THF-d8y = 7.8714x + 0.1403 R2 = 0.9909 0 2 4 6 8 10 12 00.511.5 [THF]/[THF-d8][RfH]/[RfD ]

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126 Table 4-9. Rate data for (CH3)2CHOH/(CD3)2CDOD competition [IRfSO3Na] (mol L-1) [(CD3)2CDOD] (mol L-1) [(CH3)2CHOH]/ [(CD3)2CDOD] [ 3H]/[ 3D] a 0.011 0.688 0.150 1.04 0.011 0.704 0.334 1.99 0.011 0.694 0.492 2.98 0.011 0.704 0.656 4.05 0.011 0.694 0.832 4.95 0.011 0.694 1.00 5.96 a. all yields over 98% Figure 4-13. Plot of [ 3H]/[ 3D] vs. [(CH3)2CHOH]/[(CD3)2CDOD] kH/kD = Slope = 5.84 ( 0.10) Intercept = 0.121 ( 0.063) R2 = 0.999 (CH3)2CHOH vs (CD3)2CDODy = 5.8447x + 0.1206 R2 = 0.9989 0 1 2 3 4 5 6 7 00.20.40.60.811.2 [(CH3)2CHOH]/[(CD3)2CDOD][RfH]/[RfD]

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127 Table 4-10. Rate data for CH3CH2OH/CD3CD2OD competition [IRfSO3Na] (mol L-1) [CD3CD2OD] (mol L-1) [CH3CH2OH]/ [CD3CD2OD] [ 3H]/[ 3D] a 0.011 1.24 0.123 1.17 0.011 1.25 0.266 2.30 0.011 1.23 0.400 3.42 0.011 1.24 0.521 4.34 0.011 1.24 0.753 6.52 0.011 1.22 1.03 9.12 a. all yields over 98% Figure 4-14. Plot of [ 3H]/[ 3D] vs. [CH3CH2OH]/[CD3CD2OD] kH/kD = Slope = 8.78 ( 0.18) Intercept = -0.048 ( 0.109) R2 = 0.998 CH3CH2OH vs CD3CD2ODy = 8.781x 0.0483 R2 = 0.9983 0 1 2 3 4 5 6 7 8 9 10 00.20.40.60.811.2 [CH3CH2OH]/[CD3CD2OD][RfH]/[RfD]

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128 EtOH vs EtOH-d2y = 8.1104x + 0.4433 R2 = 0.9992 0 1 2 3 4 5 6 7 8 9 00.20.40.60.811.2 [H]/[D][RfH]/[RfD]Table 4-11. Rate data for CH3CH2OH/CH3CD2OD competition [IRfSO3Na] (mol L-1) [CH3CH2OH] (mol L-1) [CH3CH2OH]/ [CH3CD2OD] [ 3H]/[ 3D] a 0.011 .165 .136 1.44 0.011 .315 .259 2.62 0.011 .457 .375 3.56 0.011 .622 .506 4.56 0.011 .922 .752 6.47 0.011 1.22 .999 8.56 a. all yields over 98% Figure 4-15. Plot of [ 3H]/[ 3D] vs. [CH3CH2OH]/[CHCD2OD] kH/kD = Slope = 8.11 ( .117) Intercept = .443 (.068) R2 = .999

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129 Acetone vs. Acetone-d6y = 17.028x 0.0074 R2 = 0.9975 0 1 2 3 4 5 6 7 8 00.050.10.150.20.250.30.350.40.45 [(CH3)2CO]/[(CD3)2CO][3H]/[3D]Table 4-12. Rate data for (CH3)2CO/(CD3)2CO competition [IRfSO3Na] (mol L-1) [(CD3)2CO] (mol L-1) [(CH3)2CO]/ [(CD3)2CO] [ 3H]/[ 3D] a 0.011 2.40 0.110 1.88 0.011 2.40 0.167 2.84 0.011 2.38 0.208 3.44 0.011 2.41 0.282 4.77 0.011 2.42 0.305 5.35 0.011 2.43 0.407 6.86 a. all yields over 98% Figure 4-16. Plot of [ 3H]/[ 3D] vs. [(CH3)2CO]/[(CD3)2CO] kH/kD = Slope = 17.0 ( 0.04) Intercept = -0.007 ( 0.0008) R2 = .998

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130 Table 4-13. Rate data for CH3COOH/CD3COOD competition [IRfSO3Na] (mol L-1) [CD3COOD] (mol L-1) [CH3COOH]/ [CD3COOD] [ 3H]/[ 3D] a 0.011 3.15 0.100 2.38 0.011 3.12 0.151 3.60 0.011 3.12 0.206 5.10 0.011 3.10 0.256 6.03 0.011 3.12 0.303 6.90 0.011 3.12 0.352 8.03 a. all yields over 98% Figure 4-17. Plot of [ 3H]/[ 3D] vs. [CH3COOH]/[CD3COOD] kH/ kD = Slope = 22.2 ( 0.7) Intercept = 0.287 ( 0.179) R2 = 0.996 CH3COOH vs CD3COODy = 22.162x + 0.2871 R2 = 0.9956 0 1 2 3 4 5 6 7 8 9 0.050.10.150.20.250.30.350.4 [CH3COOH]/[CD3COOD][RfH]/[RfD]

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131 HFIPO vs HFIPO-Dy = 5.8798x + 0.2427 R2 = 0.984 2 2.5 3 3.5 4 4.5 5 5.5 0.350.40.450.50.550.60.650.70.750.80.85 [H]/[D][RfH]/[RfD]Table 4-14. Rate data for hexafluoroisopropoxide/hexafluor oisopropoxide-d competition a. all yields over 98% Figure 4-18. Plot of [ 3H]/[ 3D] vs. [(CF3)2CHO]/[CF3)2CDO] kH/ kD = Slope = 5.88 ( .433) Intercept = .243 ( .267) R2 = .984 [IRfSO3Na] (mol L-1) [(CF3)2CHO] (mol L-1) [(CF3)2CHO]/ [CF3)2CDO] [ 3H]/[ 3D] a 0.011 .109 .417 2.74 0.011 .136 .522 3.36 0.011 .163 .626 3.75 0.011 .177 .678 4.21 0.011 .204 .782 4.94

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132 Hexadeuteroisopropanol vs THFd8y = 8.9184x + 0.1996 R2 = 0.9951 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0.10.150.20.250.30.350.40.45 [H]/[D][RfH]/[RfD]Table 4-15. Rate data for hexadeuteroisopropanol/THF-d8 competition [IRfSO3Na] (mol L-1) [(CD3)2CHOH] (mol L-1) [(CD3)2CHOH]/ [THF-d8] [ 3H]/[ 3D] a 0.011 .252 .112 1.19 0.011 .496 .220 2.08 0.011 .592 .262 2.58 0.011 .675 .296 2.94 0.011 .820 .361 3.42 0.011 .930 .411 3.81 a. all yields over 98% Figure 4-19. Plot of [ 3H]/[ 3D] vs. [(CD3)2CHOH]/[THF-d8] kH/ kD = Slope =8.92 (.311) Intercept = .199 (.091) R2 = .995

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133 APPENDIX SELECTED NMR SPECTRA The following NMR spectra have been instrumental in the determination of absolute rate constants using the compet ition methodology in Chapters 2 and 3. The 1NMR spectrum for CH3CHDOH has also been include d as a key spectra for the determination of -secondary isotope effects in Chapter 4.

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134 Figure A-1. 19F NMR spectra for ICF2CF2OCF2CF2SO3Na ( 1 )

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135 Figure A-2. 19F NMR of 3H and 3D after a competition experiment

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136 Figure A-3. 19F NMR spectra of hydrogen and deuterium reduced products ( 3H/3D)

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137 Figure A-4. 1H NMR spectra CH3CHDOH

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138 Figure A-5. 1H NMR spectra showing diethy l ether impurity at 3.425 ppm

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146 BIOGRAPHICAL SKETCH Joseph Aaron Cradlebaugh was born on May 17, 1977, in Cuyahoga Falls, Ohio. At a young age, Joe moved with his parents to Cl earwater, Florida. Most of his free time as a teenager was spent on the soccer field or the track. While not immersed in such activities Joe could usually be found at Indi an Rocks Beach. Upon graduation from high school in 1996, he attended the University of North Florida in Jacksonville. Joe continued with soccer, playing on teams in Jacksonville and Clearwater. He received a Bachelor of Science degree in chemistry in 2000. In 2001, Joe started his Ph.D. work in the Department of Chemistry at the University of Florida. With a strong intere st in physical organic chemistry, he joined Professor Dolbiers group. Joe has been pe rforming research in many areas of organic fluorine chemistry. Some of these include th e kinetic studies of fl uoalkyl radicals, the reactivity of SF5Br with alkenes, and the synthe sis of novel fluorinated compounds. Joe still is an avid soccer fan, and spends most of his free time either volunteering at Youth Soccer of Gainesville, or officiati ng soccer games throughout Florida. He also enjoys running and hockey.