• TABLE OF CONTENTS
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 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Introduction
 Experimental
 Spin-spin coupling in saturated...
 Spin-spin coupling in olefinic...
 Summary
 Reference
 Appendix
 Biographical sketch
 Copyright














Title: Nuclear spin-spin coupling in fluorocarbon derivatives.
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Title: Nuclear spin-spin coupling in fluorocarbon derivatives.
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Table of Contents
    Title Page
        Page i
    Acknowledgement
        Page ii
    Table of Contents
        Page iii
    List of Tables
        Page iv
        Page v
    List of Figures
        Page vi
        Page vii
        Page viii
    Introduction
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
    Experimental
        Page 6
        Page 7
    Spin-spin coupling in saturated fluorocarbons
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
    Spin-spin coupling in olefinic fluorocarbons
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
    Summary
        Page 79
        Page 80
    Reference
        Page 81
        Page 82
    Appendix
        Page 83
        Page 84
        Page 85
        Page 86
    Biographical sketch
        Page 87
        Page 88
    Copyright
        Copyright
Full Text











NUCLEAR SPIN-SPIN COUPLING IN

FLUOROCARBON DERIVATIVES












By
KERMIT CECIL RAMEY


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










UNIVERSITY OF FLORIDA
June, 1963















ACKNOWLEDGMENT


The work described in this dissertation was carried out

at the University of Florida, Gainesville, Florida, in the years

1961 and 1962.

The extensive help and guidance of Dr. W. S. Brey, Jr.,

chairman of the author's supervisory committee, is sincerely

appreciated.















TABLE OF C,..i;TZ-TI


Page


ACKNOWLEDGMENT
LIST OF TABLES
LIST OF FIGURES

Chapter

I INTRODUCTION


II EXPERIMENTAL

III SPIN-SPIN COUPLING IN SATURATED FLUOROCARBONS

Experimental Results

Discussion and Conclusions

IV SPIN-SPIN COUPLING IN OLEFINIC FLUOROCARBONS

Experimental Results

Discussion and Conclusions

V -i: L.7'


LIST OF REFERENCES
APPENDIX I
BIOGRAPHICAL SKETCH


THEORY OF NUCLEAR SPIN-SPIN COUPLING














LIST OF TABLES


Table Page

1. The temperature dependence of 1-2 observed
in A. pure liquid CF3CFCl2, B. CF2CF2COOH in solution
in CFCi3, and C. CF3CFN02CF2NO2 in solution in CFC13 11

2. The temperature dependence of observed in CF2BrCFBrCl in solution in CFC13 11

3. The temperature dependence of (JFF 1-2 observed in
A. pure liquid CF2BrCFBr2, B. CF2BrCFBr2 in solution in
CHC3013, and C. CF2BrCFBr2 in solution in CF3CC1CC12 12

4. The nuclear spin-spin coupling constants of the
rotational isomers of CF2BrCFBrCl 23

5. The temperature dependence of -JFF\ 1-3 observed in
A. CF3CFN02CF2N02 in solution in CFC13, B. liquid
CF3CF2CF2NFCF3 and C. liquid CF3CC12CF2NF2 25

6. The temperature dependence of 1-4 observed in
A. liquid CFsCF2CF2NFCF3 and B. liquid CF3CC12CF2NF2 25

7. The temperature dependence of JFF> ab, JFF' ac and JFF' a'c observed in CF2C1CFClCFC12
in solution in CFC13 27

8. The temperature dependence of aJFF be and (JFF> aa'
observed in CF2C1CFCICFC12 in solution in CFC13 27

9. The effect of solvent upon the F-F coupling constants
in the fluoroolefin FaFbC=CFxCF2Cly 41

10. The chemical shifts for some fluoroolefins of the type
at 300C FaFbC=CXY 42

11. The temperature dependence of JFF> a-b observed in
fluoroolefins of type FaFbC CFZ 43

12. The temperature dependence of fluoroolefins of type FaFbC CFxY 44

iv








LIST OF TABLES (Continued)


Table Page
13. The temperature dependence of b-y observed
in fluoroolefins of type FaFbC CFxY 45

14. The temperature dependence of in fluoroolefins of type FaFbC CFxY 46

15. The temperature dependence of in fluoroolefins of type FaFbC CFxY 47
16. The temperature dependence of in fluoroolefins of type FaFbC CFXY 48

17. The temperature dependence of a-b observed
in fluoroolefins of type FaFbC CHxY 54

18. The temperature dependence'of a-x observed
in fluoroolefins of type FaFbC CHxY 55

19. The temperature dependence of (JFF b-y observed
in fluoroolefins of type FaFbC CHxY 56

20. The temperature dependence of in fluoroolefins of type FaFbC CHxY 57

21. The temperature dependence of b-x observed
in fluoroolefins of type FaFbC CHxY 58
22. The temperature dependence of (JFH> x-y observed
in fluoroolefins of type FaFbC CHxY 59
23. The fundamental vibrational frequencies of CF2 = CClBr
as taken from reference (27) (in cm-1) 68
24. The nuclear spin-spin coupling constants observed
in CF2CFCOF 73
25. The nuclear spin-spin coupling constants for some
fluoroolefins at 300 FaFbC CXY 77













LIST OF FIGURES


Figure Page

1. The temperature dependence of 1-2 observed
in liquid CF3CFCl2. The chemical shifts are -0.4
and +7.4 ppm relative to external CF3COOH for the
CFC12 and CF3 groups, respectively 13

2. The temperature dependence of (JFF> 1-2 observed
in CF3CF2C00H in solution in CFC13. The chemical
shifts are 7.2 and 46.0 ppm relative to external
CF3C00H for the CF3 and CF2 groups, respectively 14

3. The temperature dependence of in CF3CFN02CF2N02 in solution in CFC13. The
chemical shifts for the CF3, CF2N02 and CFNO2 groups
are -1.2, 14.2 and 62.4 ppm relative to external
CF3COOH, respectively 15

4. The temperature dependence of 1-2 observed
in CF2BrCFBrCl in solution in CFC13. The dashed line
represents the data taken from reference (12),
observed in pure liquid 17

5. The temperature dependence of 1-2 observed
in CF2BrCFBr2 in: A. pure liquid, B. solution in
CH3CC13 and C. solution in CF3CC1CC12 18

6. The effect of temperature upon the F19 spectrum of
the CF2Br group in CF2BrCFBrCl in solution in CFC13 19

7. The effect of temperature upon the F19 spectrum of
the CF2Br group in CF2BrCFBrCl in solution in CFC13 20

8. The effect of temperature upon the F19 spectrum of
the CF2Br group in CF2BrCFBrCl in solution in CFC13.
The peak labeled X is assigned to an impurity 21

9. The F19 spectrum of CF2BrCFBrCl in solution in CFC13
at -1200C, where A, B, and C corresponds to the
three rotational isomers 22

10. The temperature dependence of 1-3 and
1-4 observed in liquid CF3CF2CF2NFCF3 26









LIST OF FIGURES (Continued)


Figure

11. The temperature dependence of (JFF~>
ac observed in CF2CICFClCFCl2
in CFC13

12. The temperature dependence of
ab observed in CF2C1CFC1CFC12
in CFC13

13. The temperature dependence of (JFF>
in CFC13


Page


a'c and
in solution


a'b and
in solution


aa and
in solution


14. The sterically-favored conformation that is expected
to be the dominant species at the lower temperatures


15. The temperature dependence of Jab
fluoroolefins of type CF2CFY

16. The temperature dependence of Jax
fluoroolefins of type CF2CFY

17. The temperature dependence of Jby
fluoroolefins of type CF2CFY

18. The temperature dependence of Jay
fluoroolefins of type CF2CFY

19. The temperature dependence of Jbx
fluoroolefins of type CF2CFY

20. The temperature dependence of Jxy
fluoroolefins of type CF2CFY

21. The temperature dependence of Jab
fluoroolefins of type CF2CHY

22. The temperature dependence of Jax
fluoroolefins of type CF2CHY

23. The temperature dependence of Jby
fluoroolefins of type CF2CHY

24. The temperature dependence of Jay
fluoroolefins of type CF2CHY


observed in


observed in


observed in


observed in


observed in


observed in


observed in


observed in


observed in


observed in









LIST OF FIGURES (Continued)


Figure Page

25. The temperature dependence of Jbx observed in
fluoroolefins of type CF2CHY 65

26. The temperature dependence of Jxy observed in
fluoroolefins of type CF2CHY 66

27. The F19 spectrum of CF2CFCOF as observed at 300 74

28. The F19 spectrum of CF2CFCOF as observed at -1050 75


viii















CHAPTER I

INTRODUCTION


The correlation of the nuclear magnetic resonance parameters,

chemical shifts and coupling constants, with molecular electron

structure as affected by temperature, is of considerable importance,

not only for the understanding of the n.m.r. phenomenon itself

but also for the application of n.m.r. as a tool in the study of

molecular motions. The changes in structure which occur in the

temperature range accessible to n.m.r. may be classified as:

(1) molecular conformations, such as the boat-chair equilibrium

observed in perfluorocyclohexane, (2) molecular interactions, such

as hydrogen bonding, and (3) excited vibrational states.

Numerous examples of the first two classes have been

reported (1-5), and the dependence of the chemical shift upon

isotopic species (6,7) has been interpreted in terms of a

vibrational effect (8). However, an attempt to detect an isotopic

difference between the geminal H-F and D-F coupling in n-C3F7H and

n-C3F7D yielded negative results (9).

A large amount of material, both theoretical and experimental,

has been published pertaining to the effect of molecular geometry

and molecular motions upon the chemical shift and coupling constant.

A large amount of the work is attributed to Gutowsky, Karplus and

co-workers.








The work of Gutowsky, Karplus and Grant (10) on the

angular dependence of electron coupled proton interactions in

the CH2 group has enjoyed considerable success in the correlation

of molecular geometry with the corresponding coupling constant.

The results as calculated from the valence bond theory and

confirmed by a number of examples show that Jgem HH' decreases

with increasing H-C-H' angle.

The theoretical calculation of the temperature dependence

of the spin-spin coupling in substituted ethanes by Schug, McMahon

and Gutowsky (11) is of particular interest. The calculations,

based on a quantum mechanical and a classical approach, yielded

a temperature independent value of the average coupling with

respect to the torsional vibrations for those molecules which

possess a potential function of three-fold symmetry for rotation.

The experimental results are somewhat limited. One compound

CH3CH2NO2 was studied over a range of 1000, and no change of

coupling constant with temperature was found.

Gutowsky, Belford and McMahon (12) investigated the

conformational equilibria in a number of substituted ethanes

and found that the relative energies of the rotamers as obtained

by n.m.r. agreed very well with those obtained from vibrational

spectra. The basic assumption used in the calculations was that

the temperature dependence of the chemical shifts and coupling

constants results only from a change in the equilibrium concentration

of rotamers.

Similar investigations, using the above assumptions, were

made by Fessenden and Waugh (13) and Abraham and Bernstein (14).









Furthermore, Fessenden and Waugh assumed that the coupling depends

only on whether the two nuclei are gauche or trans and not upon

the structure of each rotamer.

A second method of calculating the potential energy as a

function of internal rotation in substituted ethanes was proposed

by Thompson, Newmark and Sederholm (15). They utilized the Boltzmann

energy distribution to calculate the free energy associated with

the various rotamers from their integrated areas as obtained from

the F19 n.m.r. spectra at various temperatures. This method is

limited to those compounds for which rotational isomers can be

frozen-out.

The results of Powles and Strange (16) for the temperature

dependence of the spin-spin coupling in CH3CHO show a small but

significant change over a range of 700. This change is interpreted

in terms of the internal motion of the molecule where the coupling

is dependent upon the dihedral angle between the plane of the CHO

group and the plane of the C-C'-H group for a given proton of the

methyl group.

The postulate of Petrakis and Sederholm (17), that the

spin-spin interaction in saturated fluorocarbons is transmitted

by the overlap of the electron cloud of one fluorine atom with

the nucleus of a second, accounts very well for the large value of

1-3 coupling compared to the very small value of 1-2 coupling

observed in most instances. A correlation of JFFr with the

internuclear separation was predicted from a consideration of:

(1) the observed geminal coupling of 284 cps in perfluorocyclo-

hexane corresponding to a separation ofev2.17A, (2) the observed








near zero coupling between 1-2 fluorines which are separated

"V2.73A in two of the three possible staggered configurations in

the group CF3-CF2- is taken as the zero point, and (3) a value of

54 cps is assigned to the 1-3 coupling in the group CF3-CF2-CF2,

resulting from two of the nine possible staggered configurations

corresponding to an internuclear separation of A/2.51A and the

observed average coupling of 12 cps, so that (9/2)12 = 54. This

postulate has survived some criticism (18) even though positive

evidence is lacking.

Recently, Petrakis and Sederholm (19) have observed

a temperature dependence of the chemical shift in a number of

hydrocarbons. The observed changes were very small; however,

they are significant and were attributed to the excitation of

the various vibrational modes within the molecule.

The detailed nature of spin-spin coupling in fluorocarbons

and related compounds presents a seemingly endless number of

problems. Not only is the mechanism of F-F coupling in considerable

doubt, but also just what molecular motions actually influence the

coupling constants is unknown. Some of the questions that one

would like to answer are: (1) how is the magnitude of this

interaction related to the nature of the bond between atoms,

(2) in systems such as F-C-C'-F', is the magnitude of the coupling

related to the dihedral angle between the two C-F bonds, (3) are the

thermal vibrations large enough to actually influence the coupling

constant by changing the average value of the various angles from

that of their equilibrium position in the lower vibrational states,

and (4) in substituted ethanes of the type CF2X-CF2Y, is the









interaction of the groups X with Y a steric effect, or is there a

noncylindrical electron distribution around the C-C' bond as

suggested by some investigators?

The purpose of the present investigation is to investigate

experimentally as many of the above listed problems as possible.

Emphasis has been placed upon two factors which should facilitate

the solution of the other cases. These two factors are: (1) to

determine if the thermal vibrations that exist in the vicinity of

room temperature actually influence the average value of the nuclear

spin-spin coupling and if so to what extent, and (2) to find some

evidence that will shed light upon the mechanism by which F-F

coupling is transmitted, that is, the relative extent to which the

couplings are transmitted by the overlap of the electrons of one

fluorine atom with the nucleus of the second, not directly bonded

to the first.















CHAPTER II

EXPERIMENTAL


The spectra were obtained with a Varian Spectrometer

operating at 56.4 Mc/sec. Audio-frequency modulation of the

magnetic field was used to produce side-bands which was

continuously monitored by a Hewlett-Packard frequency counter.

The coupling constants were measured graphically with the

assumption that the scan rate is linear with time. In all cases

from six to ten independent measurements were made, and the

average deviation is listed in the respective tables. The

temperature was regulated by the flow rate of dry nitrogen

through a Varian V4340 variable temperature probe assembly.

For the low temperature measurements the nitrogen was cooled by

passing it through a copper coil immersed in liquid nitrogen. A

copper-constantan thermocouple placed within the Dewar insert

was used to determine the temperature and is considered to be

accurate to within 20.

All of the compounds studied gave first-order spectra,

and the chemical shifts relative to external CF3C00H are listed

in the experimental results of chapters 3 and 4.

The difficulties encountered in obtaining a homogeneous

field at the lower temperatures were overcome by the use of a

-standard sample. An olefin exhibiting prominent fine structure

was used to adjust the field.






7


The fluoroolefins were prepared by Dr. J. Savory (20)

of this department. The saturated fluorocarbons were obtained

from Dr. J. Hynes of Duke University, North Carolina and from

Peninsular Chemresearch, Inc., Gainesville, Florida:














CHAPTER III

SPIN-SPIN COUPLING IN SATURATED FLUOROCARBONS


The temperature dependence of F-F coupling in saturated

fluorocarbons should yield information not only about the structure

and behavior of these molecules, but should also shed some light

upon the mechanism by which spin-spin coupling is transmitted.

The values of the F-F coupling constants in a number of substituted

fluorocarbons have been measured over temperatures ranging from

-1000 to 1000. The experimental results are discussed below.



Experimental Results


The fluorine spectrum of CF3CFC12 is that of an a3x

type and consists of a quartet for the CFC12 group and a doublet

for the CF3 group. The chemical shifts for the CF3 and CFC12

groups are -0.4 and 7.4 ppm relative to external CF300H, respectively.

The values of KJFF> 1-2 observed over the range of temperatures

are listed in Table 1 and are plotted in Figure 1.

For CF3CF2C00H, the fluorine spectrum is that of an

a3x2 type and consists of a triplet for the CF3 group and a

quartet for the CF2 group. The chemical shift for the CF3 group

falls at 7.2 ppm and that for the CF2 falls at 46.0 ppm relative

to external CF3COOH. The values of 1-2 observed over the

range of temperatures are listed in Table 1 and are plotted in

Figure 2.









The fluorine spectrum of CF3CFN02CF2N02 is that of an

a3k2x type and consists of a triplet doubled for the CF3 group

and two broad humps with a small amount of resolvable fine

structure for the other two groups. The chemical shifts for the

CF3, CF2NO2 and CFN02 groups are -1.2, 14.2 and 62.4 ppm relative
to external CF3COOH, respectively. The lack of fine structure in

the multiplets belonging to the CF2N02 and CFN02 groups results

from the coupling of the fluorine atom with the magnetic moment

of the nitrogen atom and the influence of the quadrupole moment

of the nitrogen atom. Oddly enough, neither of these interactions

are observed in compounds containing the CFNO group. This is

probably due to the decrease in the amount of double bond character

in the C-N bond for the CFNO group relative to that for the CFN02

group. The values of 1-2 observed over the range of

temperatures are listed in Table 1 and are plotted in Figure 3.

The values of 1 FF 1-3 are listed in Table 5.

In the course of this work, Gutowsky, Belford and McMahon (12)

reported measurements of the coupling constants and chemical shifts

for CF2BrCFBrCl as a function of temperature. The fluorine spectrum

of this compound is that of an abx type, and the qualitative features

have been discussed previously (12). The chemical shifts for the

a, b, and x groups are -20.2, -18.4, and -10.1 ppm relative to

external CF3COOH, respectively. The reported values for the

coupling constants of the pure liquid differ slightly from those

obtained from a solution in CFC13 and are shown in Figure 4. The

differences are attributed to a solvent effect and will be discussed









in detail later. The values of Jax and Jbx observed over the

range of temperatures are listed in Table 2.

The fluorine spectrum of CF2BrCFBr2 is that of an a2x

type and consists of a doublet for the CF2Br group and a triplet

for the CFBr2 group. The chemical shift of the CF2Br group is

-20.9 ppm and that for the CFBr2 group is -9.8 ppm relative to

external CF3C00H. The values observed over the range of temperatures

are listed in Table 3 and are plotted in Figure 5.

The fluorine spectra of the CF2Br groups in CF2BrCFBr2

and CF2BrCFBrCl show an unusual temperature effect. That for

the latter is illustrated in Figures 6 through 8. The observed

broadening and decrease in resolution which sets in at about

-500 might be attributed to a viscosity effect, except for the

observation that, as the temperature is further decreased to

-1100 and -1200 for CF2BrCFBr2 (21) and CF2BrCFBrCl, respectively,

the fine structure again appears. This broadening and loss of fine

structure is attributed to the averaging which would be expected

for slow rotation about the C-C' in the interconversion of

rotational isomers. Furthermore, in CF2BrCFBrC1 this broadening

seems to affect one part of the non-equivalence quartet more than

the other. It is possible that this unequal broadening is due

to the transmission of the quadrupole moment of the bromine atom

which could have an unequal effect upon the fluorine atoms a

and b.








TABLE l.--The temperature dependence of 1-2 observed in
A. pure liquid CF3CFC12, B. CF2CF2C00H in solution in CFC13, and
C. CF3CFN02CF2N02 in solution in CFC13



A. CF3CFC12 B. CF3CF2C00H C. CF3CFN02CF2N02


Temp KFF> 1-2 Temp 1-2


900C 5.560.06 cps 850C 1.290.03 cps 9400 4.830.06 cps
81 5.620.05 70 1.360.02 74 4.850.02
58 5.660.08 56 1.400.02 62 4.850.03
30 5.7410.05 44 1.440.05 30 5.090.03
10 5.770.05 30 1.490.02 -10 5.390.04
-8 5.820.07 10 1.540.04 -64 5.7110.03
-18 5.910.05 -5 1.640.03 -92 5.880.03
-43 5.940.07 -10 1.660.05
-65 6.090.05 -29 1.700.04



TABLE 2.--The temperature dependence of ax and bx
observed in CF2BrCFBrC1 in solution in CFC13
ab x


Temp ax JFF> bx


660C 13.880.05 cps 13.610.09 cps
32 13.970.09 13.690.05
-16 14.050.07 13.680.06
-44 14.09+0.07 13.760.05











TABLE 3.--The temperature dependence of 1JFF' 1-2 observed in
A. pure liquid CF2BrCFBr2, B. CF2BrCFBr2 in solution in
CH3CC13, and C. CF2BrCFBr2 in solution in CF3CCCC1CC2



A. CF2BrCFBr2 B. CF2BrCFBr2 C. CF2BrCFBr2


Temp 1-2 Temp < FF 1-2 Temp

860C 17.060.04 850C 17.050.06 850C 16.980.04

44 17.110.05 66 17.080.05 66 16.990.04

30 17.150.03 50 17.130.05 47 17.040.03

10 17.20+0.03 24 17.240.05 6 17.150.05

-10 17.290.06 0 17.300.03 -20 17.240.06

-33 17.390.05 -12 17.320.07 -27 17.270.06

-35 17.430.08 -41 17.310.07








C F3CFC2
3C 2


1 2


, I I I I I I I ,


-75


-50


-25


0
ToC


25


50


75


Figure l.--The temperature dependence of shifts are -0.4 and +7.4 ppm relative to external CF3COOH for the CFC12 and CF3
groups, respectively.


6,2



6,0
J
cps

5.8



5.6


RA1L


-100


100








CF3CFCOOH


1 2


I I I I


-25


0
TC


25


50


75


Figure 2.--The
The
CF2


temperature dependence of chemical shifts are 7.2 and 46.0 ppm relative to external CF3COOH for the CF3 and
groups, respectively.


2.0


1.8
J
cps

1.6



1.4


1.2 1
-1C


-75


-50


100


)0







CF3C FNO2C F2NO2

1 2 3


12


I I_ I


0


-75


-50


-25


0
TC


25


50


75


100


Figure 3.--The temperature dependence of JFF 1-2 observed in CF3CFNO2CF2NO2 in solution in CFCl3'
The chemical shifts for the CF3, CF2NO2 and CFN02 groups are -1.2, 14.2 and 62.4 ppm
relative to external CF3COOII, respectively.


6.0



5.6
J
cps

5.2



4.8


44 4
-10








The fluorine spectrum for the three isomers of CF2BrCFBrCl
as obtained at -1200 is shown in Figure 9. The three rotational
isomers are designated as shown below.

Br Fx Cl

FA FF A FF A b


FX CC Ixcici BrB F

Br Br Br

A B C
The results of the temperature study of CF2BrCFBr2 (21),
where an unambiguous assignment of the isomers can be made,
indicates that the relative population of the frozen-out isomers
depends primarily upon the amount of steric interaction. The
integrated areas for the three isomers of CF2BrCFBrCl show a
ratio of 18:1:1. The assignment of isomer B is straight-forward
since the two coupling constants .Jax and Jbx are equal. However,
the coupling constants cannot be used to differentiate between
isomers A and C. Isomer A which has the Br atoms in the trans
position would be expected to have a smaller amount of steric
interaction than isomer C and thus should be the dominant species
at the lower temperatures. The spectrum corresponding to
90 per cent of the total area is accordingly assigned to isomer A.
The observed values of the coupling constants for the three isomers
of CF2BrCFBrCl are listed in Table 4.







CF2BrCFBrCI


-~ j


4--.


15.0


14.5
J
cps
14.0


13.5


13.0
-100


7Fr~


-75


-50


-25


0
T"C


25


50


75


Figure 4.--The
The


temperature dependence of 1-2 observed in CF2BrCFBrC1 in solution in CFC13.
dashed line represents the data taken from reference (12), observed in pure liquid.


I--- 4


100


i ..


h


-6--e_4


ii-it








CF2BrCFBr2


-50


Figure 5.--The temperature dependence of
B. solution in CH3CC13 and C.


JFF> 1-2 observed in CF2BrCFBr2 in:
solution in CF3CCICC12.


A. pure liquid,


17.6



17.4
J
cps
17.2



17.0


16,80-
-100


-75


-25


0
T C


25


50


75


100











CF2Br

aa'


CFBrCI

b


-590C -720C


Figure 6.--The effect of temperature upon the F19 spectrum of the CF2Br group in CF2BrCFBrCl in
solution in CFC13.












CF2BrC FBrCI

a a' b


-1100C -125C
Figure 7.--The effect of temperature upon the F19 spectrum of the CF2Br group in CF2BrCFBrC1 in
solution in CFC13.










660C


.I


-44"C


Figure 8.--The effect of temperature upon the F19 spectrum of the CF2Br group in CF2BrCFBrC1 in
solution in CFC13. The peak labeled X is assigned to an impurity.


CF2BrCFBrCI
aa' b



^__^L ./v










CF2BrCFBrCI
a a' b
-1200C


A II iI ,UU Li
A ,, ,I I -I I I I..
B II J I I I ,. I I I
C
Figure 9.--The F19 spectrum of CF2BrCFBrC1 in solution in CFC13 at -1200C, where A, B, and C
corresponds to the three rotational isomers.








TABLE 4.--The nuclear spin-spin coupling constants of the
rotational isomers of CF2BrCFBrC1



Isomer Jt(trans) Jg(gauche)


A 12.20.3 14.40.3

B ... 21.20.5

C 17.50.4 18.50.5




The fluorine spectrum of CF3CF2CF2NFCF3 consists of

five peaks which exhibit first order splitting that are typical

for a saturated fluorocarbon containing a NF group (17). The

chemical shifts of the groups proceeding from left to right are:

CF3 = 6.1, CF2 = 51.0, CF2 = 33.2, NF = 12.4, and CF3 = -7.7 ppm

relative to external CF3COOH. The values of 1-3 and

1-4 observed over the range of temperatures are listed
in Table 5 and Table 6 and they are plotted in Figure 10.

The fluorine spectrum of CF3CC12CF2NF2 consists of three

peaks which exhibit first order splitting that are characteristic

of saturated fluorocarbons containing the NF2 group (17). The

chemical shift of the CF3 group is -2.3, the CF2 group falls at

29.8 and the NF2 group falls at -101 ppm relative to external

CF3C00H. The values of 1-3 and 1-4 observed

over the range of temperatures are listed in Tables 5 and 6.

The fluorine spectrum of CF2C1CFClCFC12 is that of an

aa'bc type and consists of three multiplets. The chemical shifts

for the various groups are: a = -19.5, a' = -17.4, b = 42.0,









and c = -15.2 ppm relative to external CF3C00H. The temperature

dependence of the coupling constants was obtained by observing the

peaks aa' and b which correspond to the CF2Cl and CFC1 groups,

respectively, over the temperature range. The observed values

of the six coupling constants are listed in Tables 7 and 8 and

are plotted in Figures 11 through 13.



Discussion and Conclusion


The temperature dependence of

The change of JFF' 1-2 with temperature as observed

in CF3CFC12 and CF3CF2000H is small but certainly significant.

For these molecules, the number of molecular motions that may

influence the electronic structure is somewhat limited. The

three rotational isomers of each compound are identical, thus

eliminating any conformational effects. The two remaining

factors that would seem most likely to influence the temperature

dependence of the coupling constants are: (1) the effect of

intermolecular interactions, i.e., solvent effects, and (2) the

excitation of the various vibrational modes in the molecule.

The existence of a temperature dependent solvent effect is ruled

out on the basis of some experimental results which are presented

in the following section. Consequently, it seems reasonable

to ascribe the temperature dependence of Ji-2 in these molecules

to the excitation of the various vibrational modes. The

separation of the contributions of the various modes would

require a detailed I. R. study as well as a detailed knowledge

of the angular dependence of J and has not been attempted.









TABLE 5.--The temperature dependence of (JFF> 1-3 observed in
A. CF3CFN02CF2N02 in solution in CFC13, B. liquid
CF3CF2CF2NFCF3 and C. liquid CF3CC12CF2NF2




A. CF3CFN02CF2N02 B. CF3CF2CF2NFCF3 C. CF3CC12CF2NF2


Temp KJFF> 1-3 Temp FF> 1-3 Temp (JFF> 1-3


940C 8.900.10 cps 940C 9.110.06 cps 660C 10.740.06 cps

74 8.620.06 30 8.730.05 80 10.640.09

62 8.550.04 5 8.650.10 5 10.490.07

30 8.490.05 -34 8.410.12 -38 10.450.06

-64 8.160.03 -60 8.3060.07 -56 10.220.06

-92 7.920.05 -81 8.090.04





TABLE 6.--The temperature dependence of 1-4 observed in
A. liquid CF3CF2CF2NFCF3 and B. liquid CF3CC12CF2NF2




A. CF3CF2CF2NFCF3 B. CF3CCl2CF2NF2


Temp JFF > 1-4 Temp JFF > 1-4


4.290.04 cps

3.790.09

3.610.05

3.280.04

3.090.08

2.9410.05


6600

30

5

-38

-56


3.590.03 cps

3.410.03

3.280.02

3.030.07

2.910.04


9400

30

5

-34

-60

-81


III







C F3CF2CF2 NFC 3

1 2 3 4 5 13
11
9


J8 Q J14
cps4



3



-100 -75 -50 -25 0 25 50 75 100
TC
Figure 10.--The temperature dependence of JFF> 1-3 and 1-4 observed in liquid
CF3CF2CF2NFCF3 .








TABLE 7.--The temperature dependence of a'c observed in CF2CIFCFC 12FCI in
solution in CFC13



Temp JFF> ab JFF1 a'b ac a'c


7000 6.170.06 cps 9.540.02 cps 12.900.08 cps 17.510.08 cps
5 5.38+0.05 10.22 0.09 12.80+0.09 19.90+0.21
-37 4.67+0.08 10.81+0.07 12.700.10 22.000.11
-56 4.12+0.11 11.11+0.08 12.62+0.17 23.66-0.14

-80 3.280.05 11.600.09 12.400.12 25.60.13
-99 28.00.27



TABLE 8.--The temperature dependence of JFF> be and (JFF> aa'
observed in CF2C1CFC1CFC12 in solution in CFC13


be




820C 15.630.11 cps 166.40.5 cps
30 15.600.09 166.00.6
-8 15.560.09 165.50.9
-43 15.420.08 164.30.8
-80 15.400.09 163.010.7


Temp







28


CF2CICFCICFC 2

24aa' b c



20
J a'c
cps
16-

14r
ac

1 2 1, '
-100 -75 -50 -25 0 25 50 75 100
TC
Figure ll.--The temperature dependence of a'c and ac observed in CF2C10FCICFCl2 in
solution in CFCl3.










CF2CICFCICFCI2

Saa b c

ab



a'b


I L 1r I _ I


-50


-25


25


50


75


100


ToC


Figure 12.--The temperature dependence of
in solution in CFC13.


JFF> a'b and


ab


observed in CF2CICFCICFC12


13


1


J
cps


9L


3 L


-100


-75








CF2CICFCICFC 2 uu--
166
aa' b c


164
J
cps

162



16 Jbc


15
----


-100 -75 -50 -25 0 25 50 75 100
TC
Figure 13.--The temperature dependence of aa and be observed in CF2CICFC1FCl12
in solution in CFC13.








The observed change of ' 1-2 with temperature
appeared to conflict with the theoretical calculations of Schug,

McMahon and Gutowsky (11). In this calculation a temperature

independent value of JHH'> 1-2 was predicted with respect to
the torsional vibrations. However, these calculations are not
expected to apply to F-F interactions since they are based on
the contact electron-spin interaction term only. The calculations
on the effect of torsional vibrations upon 1-2 will be
rather difficult and must await further calculations on the
effect of the electron-orbital and dipolar electron-spin terms
upon 1-2 relative to the dihedral angle.
The observed temperature dependence of CF3CFC12 and CF CFC200H not only hinders the use of n.m.r. as a
tool in the study of configurational isomerism but seems to cast
doubt upon the results obtained by a number of investigators (12-14)
The basic assumption in these investigations was that the
temperature dependence of 1-2 in fluoroethanes results
only from a change in the equilibrium concentration of rotational
isomers. It seems rather probable that the vibrational effects

as observed in the 'above compounds are also present in other substi-
tuted fluorocarbons.
The temperature dependence of 1-2 as observed in

CF2BrCFBrCl and CF2BrCFBr2 may be attributed to two factors:
(1) a change in the concentration of rotational isomers, and
(2) the excitation of the various vibrational modes in the
molecule. It seems impossible at present to separate these two
contributions to the temperature dependence of KJFF> 1-2'








Consequently any discussion of the relative change in the

concentration of rotational isomers as derived from the temperature

dependence of JFFP 1-2 is somewhat uncertain.

In general, it seems that the excitation of the vibrational

modes decreases the value of JPFF 1-2. In two compounds

CF2BrCFBrCl and CF2BrCFBr2 a complete analysis of JPFF> 1-2 for
the individual isomers at low temperature as well as the average

value at various higher temperatures has been made. The coupling

constants for the individual isomers of CF2BrCFBr2 (21) are

Jt = 16.2 cps and Jg = 18.6 cps for the two mirror images with
the bromine atoms in the trans position, and J = 18.8 cps for

the other rotational isomer which is present to the extent of

about five per cent at -1100. These results indicate that the

average value of 1-2 for the three rotational isomers

of CF2BrCFBr2 should increase with increasing temperatures until

equal concentrations of the three are obtained. The observed

results as shown in Figure 5 show a decrease in the average value

of 1-2 with increasing temperatures. This decrease may

be interpreted in terms of vibrational effects which override

the change produced by the change in the equilibrium concentration

of rotational isomers. Actually, the validity of predicting the

average value of (JFF> 1-2 for the equilibrium concentration of

rotational isomers from the value of Jg and.Jt of the individual

isomers is somewhat questionable since no consideration is given

to the intermediate states between the strictly gauche and the

strictly trans conformations.







Similar considerations for CF2BrCFBrCl indicate that
one of the 1-2 coupling constants should increase and one should
decrease with increasing temperatures. Again the observed results
(Figure 4) are opposite to that predicted from consideration of
the equilibrium concentration of isomers and again the discrepancy
is attributed to the vibrational effects.
The result of using the temperature dependence of (JFFp 1-2
to calculate the energy differences and the potential barriers
between the various rotational isomers and the coupling constants
in the isomers is illustrated below. The observed values of the
coupling constants for the three rotational isomers of CF2BrCFBrC1
along with the calculated values (12), which are based on the
seemingly doubtful assumption that the temperature dependence of

rotational isomers, are listed below.

Br FX Cl
A F A A F
a b x CI x b x x b


F, CI CI Br Br F

Br Br Br
A B C

Observed: J = 12.2 cps Jt = 17.5
Jg = 14.4 Jg = 21.2 cps Jg = 18.5

Calculated: t = +41.6 Jg = -10.5 J = +5.3
(12) Jg = 8.9 Jg' = -12.0 Jg = +38.7








These results seem to indicate that an additional effect other

than that of a change in the concentration of rotational isomers

is present.

The mechanism of (JFF' 1-2


The application of the through-space interaction mechanism (17)

to the temperature dependence of J1-2 cannot be made, since an

a priori prediction of the change of internuclear separation of

F1 relative to F2 with temperature cannot be made.

The results for JFF> 1-2 for the individual isomers of

CF2BrCFBrCl and CF2BrCFBr2 (21) seem to indicate that the 1-2
coupling of fluorine atoms takes place via the bonding electrons.

The through-space interaction postulate would predict that Jg Jt.

In these compounds Jg is greater than Jt; however, the difference

is considerably less than that which is predicted. The application

of the through-space interaction mechanism to account for the large

values of 1-2 observed in (CF3)3CF (17), CF3CFC12 (22) and a

number of other substituted fluoroethanes is somewhat questionable.

Recent results on CF3CFH2 and CF3CF2H (23) ( 1-2 = 15.5 and

2.8 cps, respectively) seems to indicate that factors other than

that of steric interaction are important. The evidence is certainly

not conclusive by any means, but it does seem to point in the

direction of a through-the-bond mechanism for (JFF> 1-2

The effect of solvent upon 1-2


The reported average values of Jax and Jbx in CF2BrCFBrC1

in the pure liquid (12) differ slightly from those obtained in









solution in CFCl3 (Figure 4). The difference is attributed to

the solvent. If the more polar solvent shifts the equilibrium

concentration of rotational isomers in the direction of the

most polar isomer, which is postulated to be B, as shown above,

then the value of Jbx which corresponds to Jg should increase

and Jax which corresponds to Jt should decrease. The results

confirm this shift, if it is assumed that CF2BrCFBrCl is more

polar than CFC13, which seems reasonable. This corresponds to

the general rule (24) that the more polar solvent stabilizes

the more polar isomer. The three isomers of CF2BrCFBrCl along

with the respective coupling constants were shown above.

CF2BrCFBr2 appears to behave in a similar manner, as shown in

Figure 5, although the relative polarity of the various solvents

is somewhat questionable.


The temperature dependence of 1-3


The temperature dependence of JFF> 1-3 is attributed

to: (1) the excitation of the various vibrational modes in the

molecule, and (2) a change in the equilibrium concentration of

rotational isomers having different 1-3 coupling constants. The

consistency in the direction and magnitude of change for the

three compounds studied seems to indicate that the latter factor

is small if not nonexistent.


The temperature dependence of 1-4


The temperature dependence of the 1-4 coupling constant

is quite similar to that of the 1-3 coupling constant both in









magnitude and direction. These changes are also attributed to

the same factors as the 1-3 coupling.


The temperature dependence of the coupling
constants in CF2ClCFClCFCl2


The temperature dependence of the spin-spin coupling

constants in CF2OFC1CFC12 is of considerable interest. The

object of studying this compound in the first place was to test

the through-space interaction mechanism. This was to be accom-

plished by freezing-out the various rotational isomers from

which the internuclear separation of the various fluorine atoms

could be approximated and compared with the observed coupling

constants. Unfortunately, the isomers could not be frozen out

at -1300. However, the large temperature dependence of one of

the 1-3 coupling constants, a change of 11 cps over the temperature

range covered, seems to indicate that the mechanism is operative.

In view of the fact that the internuclear separation of substi-

tutents in the 1-3 position may be considerably less than that

for substitutents in the 1-2 position, and on the assumption that

the order of repulsion is C1-C1 Cl-F F-F, it is possible to

predict the dominant conformational isomer expected at the lower

temperatures. This isomer is shown in Figure 14. At the lower

temperature, therefore, the fluorine atom a' would tend to be in

a position of near proximity to fluorine atom c a larger portion

of the time than at the higher temperature. Thus, the application

of the through-space interaction mechanism could very well account

for the large increase of Ja'c with decreasing temperatures. The










i11

I,


CI


NC
I

F
Cl


CI


Figure 14.--The sterically-favored conformation that is expected to be the dominant species
at the lower temperatures.






38

temperature independent value of Jac may be due to the accidental

cancelling which could result from the change in the equilibrium

concentration of rotational isomers, or it could indicate that

part of the 1-3 coupling is indeed transmitted through the

bonding electrons.















CHAPTER IV

SPIN-SPIN COUPLING IN OLEFINIC FLUOROCARBONS

Experimental Results


The effect of solvent upon (JFF>


As yet, relatively little is known concerning the dependence

of molecular interactions upon the F-F coupling constants. To

investigate this effect, the coupling constants of CF2 = CFCF2C1

were observed in three solvents: (1) as a pure liquid, (2) in

solution in CFC13, and (3) in solution in CH3CC13. The values

observed over the range of temperatures are listed in Table 9.

The results show a small deviation among the three solvents,

however, the difference is less than the experimental error in

most cases and appears to be insignificant. It is concluded

from these results that molecular interactions have a negligible

effect upon olefinic F-F coupling constants.


Temperature dependence of the coupling constants in fluoroolefins
of the type CF2 = CFY, where Y = CF3, CF2Cl, CF2Br, and COF


From a consideration of the generalizations as derived from

the theoretical (25) and experimental (26,27) work on the nuclear

spin-spin coupling constants in fluoroolefins, it is possible to

assign unambiguously the multiplets corresponding to the various

nuclei. These generalizations are: (1) JFF' trans is much larger








than JFF' cis in all reported cases, (2) JFF' geminal is usually

larger than JFF' cis but less than JFF' trans, and (3) the

chemical shift of a fluorine atom in the x position in the group

FaFbC = CXY falls in the range of 90 to 100 ppm above CF3C00H. -All

of the compounds have first-order spectra, and the chemical shifts

relative to external CF3COOH observed at 300 are listed in

Table 10.

The changes of the olefinic F-F coupling constants with

temperature are relatively small; however, they seem to be

clearly significant. The values observed for the six coupling

constants Jab, Jax, Jby, Jay, Jbx, and Jxy over the temperature

range are listed in Tables 11 through 16 and are plotted in

Figures 15 through 20, respectively.


Temperature dependence of the coupling constants in fluoroolefins
of the type CF2 = CHY, where Y = CF2C1, CF2I, and COF


Similar generalizations of the H-F and F-F olefinic

coupling constants in fluoroolefins of the type CF2 = CHY may

be formulated from the work of Karplus (25) and Swalen and

Reilly (26). These are: (1) JHF trans is larger than JHF cis

in all reported cases, and (2) JHF cis is usually very small,

one or two cps in most cases.

The values observed for the six coupling constants

Jab, Jax, Jby, Jays Jby, and Jxy over the temperature range are
listed in Tables 17 through 22 and are plotted in Figures 21

through 26.










TABLE 9.--The effect of solvent upon the F-F coupling
constants in the fluoroolefin

Fa Fx
//x


Fb CF2Cl
y


Coupling Temp Pure 50% 50%
Constant OC Liquid CFC13 CH3CC13


Jay 580 6.10.1 6.10.1 6.10.1
ay 300 6.10.1 6.110.1 6.00.1
-500o 5.60.1 5.70.1 5.60.1
-900 5.30.1 .5.40.1 5.40.1

J 580 17.90.1 18.10.1 18.20.2
S300 18.00.1 17.90.2 18.20.2
-500. 18.50.1 18.5+0.1 18.60.2
-900 18.70.2 19.00.3 19.10.1

Jy 58 30.00.2 29.90.2 29.80.3
y30 30.00.2 30.10.3 30.00.2
-50 32.00.3 31.70.2 32.10.3
-90 33.50.2 33.40.3 33.40.3

Jab 58 56.90.3 57.20.3 56.70.3
30 56.80.4 56.50.3 56.30.4
-50 55.80.3 55.70.2 55.90.3
-90 54.90.4 55.00.3 54.90.5

J 58 39.20.2 39.20.2 38.90.3
30 39.00.3 38.60.4 38.70.4
-50 37.50.3 37.40.3 37.60.3
-90 37.00.3 36.90.3 37.10.4











TABLE 10.--The chemical shifts for some fluoroolefins
of the type at 3000

Fa X
X Y /


Fb Y




X Y aa 5b 5x


CF3

CF2C1

CF2Br

CF2I

CF2NO

COF


CF3

CF2C1

CF2Br

CF2I

COF


-11.1

2.9

0.8

1.8

-4.9

-13.6


19.0

19.5

18.8

18.5

0.6


-6.0

-6.3

-4.3

-7.6

-8.8

-18.3


32.3

30.2

28.9

27.6

12.3


119

108

105

98.3

110


-25.2

-32.4

-37.6

-45.8

4.1

-114.4


-5.7

-18.5

-23.4

-14.9

-98.0


aThe chemical
CF3COOH.


shifts are in ppm relative to external











TABLE 11.--The temperature dependence of a-b observed
in fluoroolefins of type

Fa F

C==C

Fb



Y = CF3 Y = CF2C1 Y = CF2Br Y = COF


Temp Jab Temp Jab Temp Jab Temp Jab


5400 57.70.3 780C 57.20.4 840C 55.30.8 880C 7.020.08

30' 57.50.3 30 57.00.3 30 54.70.4 30 6.03 0.09

2 57.1 0.2 -14 56.60.6 2 54.60.1 -13 5.940.09

-30 56.8 0.3 -68 55.9+0.4 -21 54.00.3 -59 4.820.07

-99 56.20.2 -97 55.4+0.4 -71 53.60.5 -91 4.16-0.07











TABLE 12.--The temperature dependence of JFF> a-x observed in
fluoroolefins of type

F F

C=c

F/ Y



Y = CF3 Y = CF2Cl Y = CF2Br Y = COF


Temp Jax Temp Jax Temp Jax Temp Jax


540C 39.50.3 780C 39.30.3 840C 38.60.6 880C 37.00.3

30 39.310.3 30 39.10.5 30 38.10.3 30 36.70.1

2 39.10.2 -14 38.70.5 2 37.50.2 -13 36.10.2

-30 38.80.1 -68 37.70.3 -21 36.90.2 -59 35.60.5

-99 38.00.3 -97 37.20.5 -71 36.30.2 -91 34.70.2











TABLE 13.--The temperature dependence of b-y observed
in fluoroolefins of type

Fa F

C=C

Fb Y



Y = CF3 Y = CF2C Y = CF2Br Y = COF


Temp Jby Temp Jby Temp Jby Temp Jby


550C 20.90.1 780C 30.40.4 8400 30.60.4 880C 48.90.2

30 21.10.1 30 30.70.3 30 31.80.1 60 50.20.2

1 21.30.2 -14 30.90.2 2 32.20.1 30 51.80.2

-58 21.80.2 -68 32.40.2 -21 32.80.2 -13 52.80.2

-99 21.80.1 -97 33.30.2 -71 33.50.2 -37 53.50.2











TABLE 14.--The temperature dependence of a-y observed in
fluoroolefins of type

Fa Fx


C=C

/ \Y


Y = CF3 Y = CF2C1 Y= CF2Br Y = COF


Temp Jay Temp Jay Temp Jay Temp Jay


550C 8.310.05 7800 6.130.07' 840C 5.850.04 880C 15.80.1

30 8.400.08 30 6.030.07 30 5.67+0.06 60 15.50.1

1 8.310.05 -14 5.880.18 2 5.530.05 30 15.30.1

-58 8.220.09 -68 5.620.09 -21 5.480.05 -13 14.80.1

-99 8.100.08 -97 5.390.08 -71 5.240.05 -59 13.10.2











TABLE 15.--The temperature dependence of <1FF', b-x observed in
fluoroolefins of type

Fa /Fx
C=c

Fb Y



Y = CF3 Y =CF2C1 Y = CF2Br Y = COF


Temp Jbx Temp Jbx Temp Jbx Temp Jbx


540C 118.2 0.7 780C 116.0-0.6 840C 115.3-0.5 880C 114.40.4

30 118.00.8 30 116.00.5 30 115.00.4 30 114.00.5

2 117.60.5 -14 115.70.4 2 115.00.5 -13 113.60.4

-30 117.40.5 -68 115.50.6 -21 114.60.4 -59 113.00.3

-99 117.30.7 -97 115.30.5 -71 114.40.4 -91 112.60.5












TABLE 16.--The temperature dependence of< JFF>x-y observed in
fluoroolefins of type

Fa Fx


/


c=c
/ I


Y = CF3 Y = CF2C1 Y =CF2Br Y = COF


Temp Jxy Temp Jxy Temp Jxy Temp Jxy


.540C

30

1

-58

-99


12.60.05

12.90.08

12.90.10

13.40.12

13. 50.10


780C

30

-14

-68

-97


18.10.35

18.10.3

18.2-0.3

18.40.2

18.70.2


840C

30

-21

-50

-71


20.90.1

21.40.2

21.8 0.1

22.10.1

22.40.1


8800

60

30

-37

-91


31.70.3

31.90.3

32.40.1

32.60.2

34.70.5


----








ab Y CF
3


FaC Fx
1\C= C
Fh Y


57
YCFI

55-
cps Y CF2Br

53


Y =COF

4 II I I I
-100 -75 -50 -25 0 25 50 75 100
T"C
Figure 15.--The temperature dependence of Jab observed in fluoroolefins of type CF2CFY.


59









42



40
J
cps

38



36


34 -
-100


F /FX
C=C
Fb Y


A= CF
3
J B=CF2CI
ax C: CF2Br

D=COF
A
B

S----1 D
D


100


Figure 16.--The temperature dependence of Jax observed in fluoroolefins of type CF2CFY.


-75 -50 -25 0 25 50
TC











aCCFx


by
Y=COF



Y:CF2Br


54



50

34
J
cps

30


SY:CF3
3
V'"," "'3""2-"-"g^ - -i1'_-
--"^----"^a.-oaIo.


IIII I I I I


-75


-50


-25


0
TO
T"C


25


50


75


100


Figure 17.--The temperature dependence of Jby observed in fluoroolefins of type CF2CFY.


'-,, Y-CFCI
6--. 2 ,-


24


-100


-~4~


n0L









ay


Y=COF


Y=CF
3
YI


Y:CFCI .


2--


-50


-25


0
T"C


25


50


T --2 F
i


75


1


-.-
00


Figure 18.--The temperature dependence of Jay observed in fluoroolefins of type CF2CFY.


FC CF


17



15


J
cps

13

8



6


A L


-75


_ I -I ---I I-~-^~-~l~,--cL------~--- ---~rrrr~--r*---r~ -lr~-l-amts~l--------oun~-P~-------i


13 ----"icp"p~cmr'


-100


--








120 Fa\ Fx Y
_C=C bx YCF3
Fb \Y
118
J Y
II.
p - -4 rr

116

S, ,_ r- --L----' Y~ YC.OF
114 OF

112 | -- .... '.... I ---
112
-100 -75 -50 -25 0 25 50 75 100
T"C
Figure 19.--The temperature dependence of Jbx observed in fluoroolefins of type CF2CFY.











TABLE 17.--The temperature dependence of JFF' a-b observed
in fluoroolefins of type

Fa H x
a /x
C=-C

Fb Y



Y = CF2C1 Y = CF2I Y = COF


Temp Jab Temp Jab Temp Jab


660C 13.00.1 880C 9.010.16 940C 28.60.4

300 13.00.1 300 8.910.20 300 30.40.3

-25 12.80.2 40 8.850.11 -40 30.20.3

-84 12.40.1 -350 8.82-0.12 -250 31.8-0.4

-990 8.700.09 -550 32.90.3

-84 33.70.2











TABLE 18.--The temperature dependence of KJHF a-x observed
in fluoroolefins of type


\ /y
F Hx
C=C

Fb



Y = CF2C1 Y = CF21 Y = COF

Temp Jax Temp Jax Temp Jax


.660C 1.850.06 880C 1.1800.04 850C 1.580.03

25 1.750.08 30 1.740.05 30 1.530.02

4 1.730.04 4 1.720.05 -25 1.440.03

-30 1.630.05 -35 1.640.04 -93 1.350.04

-72 1.500.06 -99 1.410.08 -99 1.290.04










TABLE 19.--The temperature dependence of b-y observed
in fluoroolefins of type

a Hx
C=C

F/ \
Fb


Y = CF2Cl Y = CF2I Y = COF

Temp Jby Temp Jby Temp Jby

660C 22.00.2 880C 22.40.2 940C 30.40.2
30 22.00.3 30 22.90.1 30 30.20.2
-15 22.30.1 4 22.90.2 -4 30.20.3
-38 22.30.2 -35 23.40.2 -25 29.70.4
-84 23.60.2 -99 24.30.2 -55 29.010.2
-99 24.20.2 -84 28.30.3











TABLE 20.--The temperature dependence of FF' a-y observed
in fluoroolefins of type

Fa H
\ /

Fb Y



Y = CF2Cl Y = CF2I Y = COF


Temp Jay Temp Jay Temp Jay


6600 9.21-0.11 880C 8.66-0.10 940C 33.3-0.2

30 9.260.10 30 8.780.21 30 34.50.4

-15 9.220.20 4 8.610.14 -4 35.30.4

-38 9.310.09 -35 8.720.14 -25 35.60.3

-98 9.370.16 -99 8.680.12 -55 37.00.4

-84 37.40.3











TABLE 21.--The temperature dependence of JFH b-x observed
in fluoroolefins of type '

F H
a x
0= /Hx
C=C

Fb Y



Y = CF2C1 Y = CF2I Y = COF


Temp Jbx Temp Jbx Temp Jbx


660C 20.70.1 880C 21.00.2 850C 20.70.2

25 20.8+0.2 30 21.3 0.1 30 20.80.2

0 20.90.1 4 21.30.2 -25 20.90.3

-30 20.90.1 -35 21.4 0.3 -93 21.00.2

-72 21.00.1 -99 21.50.2 -99 21.00.2

-84 21.00.2











TABLE 22.--The temperature dependence of KFl,> x-y observed in
fluoroolefins of type

Fa H
\ /
C=C

Fb Y



Y = CF2C1 Y = CF21 Y = COF


Temp Jxy Temp Jxy Temp Jxy


6600 9.210.09 880C 10.80.2 940C 3.810.04

25 9.280.07 30 11.10.1 30 3.700.05

4 9.380.12 4 11.00.1 -4 3.610.03

-30 9.510.11 -35 11.40.2 -25 3.460.03

-72 9.68+0.09 -99 11.5 0.2 -55 3.22-0.04

-84 2.860.05








a\C:C Fx

b Y


J
xy


Y=COF
Y V


-- ------ Y-CF2Br


Y= CFC I
-,;;-----_-----^^E----------


Y=:CF
3
^ ^ ------ V ---


I II II I Ir


TC


25


50


75 100


Figure 20.--The temperature dependence of Jy observed in fluoroolefins of type CF2CFY.


36


32


24
J
cps

20



16


10


-100
-100


-75


-50


-25


i








ab




b '
/ \


-Y-CF2Cl



- '- --
Y. .. F. T
;___ -----^Y-r C T


-75


-50


p_ p


-25


50


ToC


75


Figure 21.--The temperature dependence of Jab observed in fluoroolefins of type CF2CHY.


34





28


13
J
cps

12

9



8


-100


100


__


-


" 2








2.0


1.8
J
cps
1.6



1.4


1.2
-100


J
Cl


F- H
C=C
F Y
b


Y=CF I
2,


Y=CF2C


Y= COF


Figure 22.--The temperature dependence of Jax observed in fluoroolefins of type CF2CHIY.


-75 -50 -25 0 25 50 75
TC


100








Jby
Y=COF -

^^i


30


/CH


Y=CFI
2,


Figure 23.--The temperature dependence of Jby observed in fluoroolefins of type CF2CHY.


J
cps
24


23


22L-
-100


-75 -50 -25 0 25 50 75
T"C


100









da y
Y-COF



F Y


Y CF CI
2


3-A


Y=CF I
--l -4


I I I I I


-75


-50


-25


0
T"C


25


50


75


100


Figure 24.--The temperature dependence of Jay observed in fluoroolefins of type CF2CIIY.


37



33
J
cps
10


8L
-1i


_ ___~_i~-------


o I_


r -


)0











C C Hx
Fb Y


bx


24



23
J
cps

22



21


Y=CF2CI & COF
I I


-75


-50


-25


0
TC


25


50


75


Figure 25.--The temperature dependence of Jbx observed in fluoroolefins of type CF2CIIY.


Y=CF I
^-^--- --4--j~lI~j ~-2~
J ^'--^--- ^


OnL


100


- ---~'


-100








xy

1 1 Fa ,H
/C-C\ X --
F
b Y =CFI
10 -

cps
9

Y=CF2CI



Y=:COF
I ----, -- I- I .-- L
-100 -75 -50 -25 0 25 50 75 100
TC
Figure 26.--The temperature dependence of Jxy observed in fluoroolefins of type CF2CIY.









Discussion and Conclusion


With the elimination of the effects of molecular inter-

actions upon JpF', it seems reasonable to attribute the temperature

dependence of the olefinic coupling constants to the thermal

excitation of the various vibrational and rotational modes in

the molecule.

KJFF~? ab If the rotation of the Y group does not
significantly influence the molecular electronic structure of

the FaFbC = part of the molecule FaFbC = CXY, then the temperature

dependence of Jab may be attributed to the thermal excitation of

the various vibrational modes in the molecule. This assumption

seems reasonable for the compound with Y = CF3 since the three

rotational isomers are identical. For the other molecules, the

rotational effects of the Y group may influence the entire

molecular electronic structure. However, with the exception of

the compounds with Y = COF, these effects are believed to be

small. This belief is based in part upon the almost identical

temperature dependence of Jab in the compounds with Y = CF3,

CF2Cl, CF2Br, and CF2l. For the compound CF2 = CFCOF there is a

distinct difference between Jab for the two isomers (28). This

difference between Jab for the two isomers may be attributed to

a rotational effect, however, it is more than likely an electronic

effect.

The I.R. and Raman spectra of fluoroolefins of the type

CF2 = CXY show twelve fundamental normal modes of vibration, nine

of which are planar. These fundamental vibrational frequencies as









taken from Theimer and Nielson (29) are assigned as in the following

table.



TABLE 23.--The fundamental vibrational frequencies of CF2 = CClBr
as taken from reference (27) (in cm-1)



Species I. R. Raman Approximate
Gas Liquid Motion


a' 1731vs 1727vs C=C stretching
a' 1314vs 1308w CF stretching
a' 1022vs 1017m CF stretching
a' 945vs 939w CC1 stretching
a' 613s 611s CBr stretching
a' 455w 459w rocking
a' 358m 359vvs CF2 deformation
a' 219vs CClBr deformation
a' 166 rocking
a" 566s 562vs wagging
a" 320w 324vw wagging
a' 155vw twisting


planar
nonplanar


All of the molecular vibrations probably contribute to the

temperature dependence of the various nuclear spin-spin coupling

constants. However, it seems reasonable that the CF2 deformation

which is depicted below would have the most influence on the

temperature dependence of Jab*




C=C


This symmetric in-plane deformation should have an asymmetric
This symmetric in-plane deformation should have an asymmetric









potential well since the large fluorine atoms would essentially

bump into each other and the excited states should have associated

with them a larger value of the angle Fa-C-Fb than that for the

corresponding static position. The estimated number of molecules

in the excited state for this mode as calculated from the Boltzmann

distribution, is 5 per cent at -1000 and 26 per cent at 1000. This

increase seems to be large enough to influence significantly the

average value of the angle Fa-C-Fb, if the potential well is

asymmetric as postulated.

If the angular dependence of JFFI in the group F-C-F'

is the same as that for JHHII in the group H-C-H', where an increase

in the angle corresponds to an algebraic decrease in the value

of JHH' (12), then the observed increase in Jab with increasing

temperatures in both series of compounds may be explained by

assigning a negative value to Jab.

This assignment is by no means unambiguous and depends

upon a number of factors, of which, the mechanism of the inter-

action is probably the most important. The C-F stretch vibrations

should have associated with the excited states a larger average

value of the internuclear separation of Fa relative to Fb than

that for the lower vibrational states. If the through-space

interaction mechanism (19) applies, it would seem to predict a

decrease in the absolute magnitude of Jab with increasing temperatures.

However, an increase in Jab is observed with increasing temperatures

which suggests that the mechanism of interaction is not through

space even though the internuclear separation is approximately 2.5A.









This internuclear separation is considerably less than the sum

of the ionic radii 2.7Ao for which Petrakis and Sederholm (19)

have predicted that overlap and thus the through-space interaction

should occur. This argument which is based on the average inter-

nuclear separation may not apply, if, the form of the curve which

results when J is plotted versus the internuclear separation is

such that the slope increases in going from a large to a small

internuclear separation. If the C-F stretch vibration has an

asymmetrical potential well as expected, then the sum of the

product of the coupling constant which corresponds to a particular

internuclear separation, and the time that the nucleus spends at

this separation within one vibrational period may be larger than

the value of the coupling constants in the static position. That is

k=m
2 tkJk Jb which is illustrated below.
k=l


J-
J ;\

M I

m r rb r

Internuclear Separation
A second important factor in assigning a negative sign to

Jab is that the angular dependence of the H-C-H coupling constant
seems to be somewhat doubtful at the present. Recently, Bernstein

and Sheppard (30) presented some experimental results that indicate

that the calculated trend (10) in the angular dependence of the

coupling constant H-C-H' is in the wrong direction. If this is








true, then the temperature dependence of Jab may be explained

by assigning a positive sign to Jab*

The temperature dependence of Jab in the second series

of olefins, CF2CHY, is somewhat unusual in that the change of

Jab with temperature for the compound with Y = COF is opposite

to that for the other compounds. This is attributed to a change

in concentration of rotational isomers with different Jab coupling

constants and will be discussed in detail under Jby-

JFF> ax and ax The temperature dependence of
Jax is quite similar to that of Jab both in magnitude and direction.

These changes are attributed to the excitation of the various

vibrational modes in the molecule. A prediction as to the probable

sign of Jax cannot be made from the temperature dependence alone.

This is primarily due to a lack of theoretical calculations

concerning the angular dependence of JFFp and JHF in the groups

F-C-C'-F' and F-C-C'-H. However, by taking into account the work

of Evans (31) on the relative signs of fluorine spin-spin coupling

constants as determined by double irradiation, which show that

Jab and Jax are of the same sign in the series CF2 = CFY, then

Jax should also be negative in the compounds of this type. This

would indicate that the angular dependence of Jax in the group

F-C-C'-F' is opposite to that for Jab in the group F-C-F'. The

assignment of a sign to Jax in the second series of olefins CF2 = CHY

cannot be made since the relative signs have not been determined.

JFF> by The change of Jby with temperature in the
compounds with Y = CF3, CF2Cl, CF2Br and CF2I may be attributed









to both vibrational and rotational effects. For the compounds

CF2CFCOF and CF2CHCOF an additional effect must be included;

that of an equilibrium of rotational isomers.

At about -600 the peaks corresponding to the groups

b and y in Fa Fx show a broadening and a loss of fine

C=C

Fb COF

structure. This would be expected from the averaging of a

number of positions which are due to the slow rate of inter-

conversion of rotational isomers. The complete fluorine spectrum

obtained at 300 is shown in Figure 27 and the corresponding

spectrum for the two isomers as obtained at -1050 is shown in

Figure 28. The coupling constants, given in Table 24, are quite

different for the two isomers, and a rough estimate of the

relative population of the two forms can be made from either

Jay or Jby. The large differences of Jby in the two isomers

may be interpreted in terms of the through-space interaction

theory. However, a large difference is also observed for Jay*

Since the mechanism of Jay must be that of a through-bond inter-

action, the difference in Jay between the two isomers must be

due to the angular dependence of the coupling constants. This

angular dependence could, in fact, account for the large difference

observed in Jby for the two isomers.

The slope of the temperature dependence of Jby in the

compound CF2 = CHCOF is opposite to that of Jby in the other

two compounds in the series. This is quite similar to the










TABLE 24.--The-nuclear spin-spin coupling constants observed
in CF2CFCOF

Fa Fx Fa Fx

C=C --=== C=C
/ C==0 / 0-F
Fb Fy Fb 0


Mixture Isomer I Isomer II
300C -1050C -1050C


Jab = 6.00.2 4.00.2 2

Jax = 36.80.3 33.7-0.4 36.20.4
S2..
Jay = 15.40.2 2 41.60.4

Jbx = 114 1 111 1 117 1
+ + z
Jby = 51.9-0.4 84.5-1 _2

Jy = 32.2 0.3 34.4 0.4 31.1 0.4
xy




































Figure 27.--The F19 spectrum of CF2CFCOF as observed at 300.







































y' y a' a b xx'


Figure 28.--The F19 spectrum of CF2CFCOF as observed at -1050.




C-
On








results obtained for Jab and again is attributed to the temperature

dependence of the equilibrium of rotational isomers which overrides

the vibrational and rotational effects. However, the rotational

energy of the COF group in this compound is such that the isomers

are not frozen out at -130.

JFF> ay. In five of the seven compounds studied
Jay is essentially temperature independent. For the other two

compounds CF2CFCOF and CF2CHCOF a change of about three to

four cps is observed over the temperature range covered. Again

this change is attributed to the change in the equilibrium

concentration of rotational isomers.

FF> bx and temperature in all seven compounds is relatively small. A

positive sign is assigned to Jbx in the CF2 = CFY series on the

basis of the previous assignment to Jab and the relative signs

as determined by Evans (29).

xy and observed changes may be attributed to both vibrational and rotational

effects, which cannot, at present, be distinguished.

The results for the six coupling constants in the two

series of fluoroolefins as observed at 300 are summarized in

Table 25. One factor common to both series is that Jab and Jay

decrease with decreasing electronegativity of the Y group and/or

with increasing size of the Y group.

A similar trend, but in the opposite direction is observed

for Jxy and Jby. In the first series CF2 = CHY, Jax and Jbx are

essentially independent of the substituent Y. In the second series









TABLE 25.--The nuclear spin-spin coupling constants
for some fluoroolefins at 300

X /X

C=\

FT, Y


X Y Jab ax Jay Jbx Jby Jxy

H CF3 14.1 1.4 11.8 21.7 17.5 6.6

H CF2Cl 13.0 1.8 9.2 20.8 21.9 9.3

H CF2Br 10.9 1.6 9.4 21.0 22.9 9.3

H CF2I 8.9 1.7 8.7 21.3 22.8 10.8

H CF2NO 7.8 1.6 9.1 23.4 20.0 11.5

H COF 30.3 1.5 34.5 20.8 30.2 3.7


F CF3 57.6 39.4 8.4 118 21.2 13.0

F CF2C1 57.2 39.0 6.0 116 30.7 18.0

F CF2Br 55.0 38.0 5.8 115 32.0 21.4

F CF2I 53.4 36.2 5.1 115 32.6 26.0

F COF 6.6 36.8 15.5 114 51.4 32.0


aThe coupling constants are
at 56.4Mc/sec.


reported in cps and were obtained






78

CF2 = CFY, Jax and Jbx show a decrease with decreasing electro-

negativity of the Y group, however, the changes are relatively

small. It may be noted that the coupling constants of CF2CFCOF

and CF2CHCOF do not in general follow the trends as listed above

for the other compounds. This is probably due to: (1) the existence

of an equilibrium of rotational isomers in both of these compounds,

and (2) the possibility that the geometry of these molecules is

altered by the partial double bond character of the C-COF bond.














CHAPTER V

SUMMARY


It is found that the nuclear spin-spin coupling constants

in a number of saturated and olefinic fluorocarbons vary with

temperature. This effect is attributed to: (1) the excitation

of vibrational modes in the molecule, (2) the excitation of

rotational modes in the molecule, and (3) a change in the

equilibrium concentration of rotational isomers. In two compounds,

CF3CFC12 and CF3CF2COOH, a small but significant temperature

dependence of 1-2 is observed. These changes are attributed

to the excitation of vibrational modes and are interpreted as to

invalidate those n.m.r. studies of rotational isomerism in

substituted ethanes.

One of the 1-3 coupling constants in CF2C1CFCICFCl2 is

found to vary from 17 to 26 cps over the temperature range

-900 to 1000 while the other 1-3 coupling constant is virtually

temperature independent. These results are interpreted in terms

of the sterically favored conformations and the through-space

interaction mechanism of F-F coupling.

The temperature dependence of the spin-spin coupling

constants in fluoroolefins of the type Fa X is attributed
\ /
C=C
/ \
Fb Y

to the excitation of both vibrational and rotational modes in the

79








molecules. For one of the coupling constants, (JFF ab the

effect is attributed to the excitation of the vibrational modes

only, of which, the CF0 deformations are probably the most

important. These excited vibrations should have associated with

them a larger value of the angle Fa-C-Fb than that for the corre-

sponding equilibrium position in the lower vibrational states. The

data are interpreted to yield the sign of ab from: (1) the

postulated increase in the average value of the angle Fa-C-Fb with

increasing temperatures, (2) an assumed correspondence of the

angular dependence of in the group F-C-F' relative to

that for JHHI in the group H-C-H', and (3) the observed increase

in JFF> ab with increasing temperatures.














LIST OF REFERENCES


1. J. Fenney and L. H. Stucliffe, J. Phys. Chem. 65, 1894 w
(1961).

2. C. M. Huggins and G. C. Pimentel, J. Chem. Phys. 23, 1244 \
(1955).

3. C. F. Jumper, M. T. Emerson, and B. B. Howard, J. Chem. Phys.
35, 1911 (1961).

4. G. V. D. Tiers, Proc. Chem. Soc. 389 (1961).

5. L. W. Reves and W. G. Schneider, Canad. J. Chem. 35, 251
(1957).

6. G. V. D. Tiers, J. Am. Chem. Soc. 79, 5585 (1957).

7. T. F. Wimmett, Phys. Rev. 91, 476A (1963).

8. H. S. Gutowsky, J. Chem. Phys. 31, 1683 (1959). N

9. H. S. Gutowsky, V. D. Mochel, and B. G. Sommers, J. Chem.
Phys. 36, 1153 (1962).

10. H. S. Gutowsky, M. Karplus, and D. M. Grant, J. Chem. Phys.
31, 1278 (1959).
11. J. C. Schug, P. E. McMahon, and H. S. Gutowsky, J. Chem.
Phys. 33, 843 (1960).

12. H. S. Gutowsky, G. G. Belford, and P. E. McMahon, J. Chem.
Phys. 36, 3353 (1962).

13. R. W. Fessenden and J. S. Waugh, J. Chem. Phys. 37, 1466
(1962).

14. R. J. Abraham and H. J. Bernstein, Canad. J. Chem. 39,
39 (1961).

15. D. S. Thompson, R. A. Newmark, and C. H. Sederholm, J. Chem.
Phys. 37, 411 (1962).

16. J. G. Powles and J. II. Strange, Mol. Phys. 5, 329 (1962).

81








17. L. Petrakis and C. H. Sederholm, J. Chem. Phys. 35, 1243
(1961).

18. J. I. Musher, J. Chem. Phys. 36, 1086 (1962).

19. L. Petrakis and C. H. Sederholm, J. Chem. Phys. 35, 1174
(1961).

20. J. Savory and P. Tarrant (to be published).

21. S. L. Manatt and D. D. Elleman, J. Am. Chem. Soc. 84, 1305
(1962).

22. J. Lee and L. H. Sutcliffe, Trans. Faraday Soc. 55, 880
(1959).

23. D. D. Elleman, L. E. Brown and D. Williams, J. Mol. Spectr.
7, 307 (1961).

24. "S. Mizushima, The Structure of Molecules and Internal
Rotation (Academic Press, Inc., New York, 1954).

25. M. Karplus, J. Chem. Phys. 30, 11 (1959).

26. H. M. McConnel, C. A. Reilly, and A. D. McLean, J. Chem.
Phys. 24 (1956); J. D. Swalen and C. A. Reilly, ibid
34, 2122 (1961).

27. S. Andreades, J. Am. Chem. Soc. 84, 864 (1962).

28. W. S. Brey, Jr. and K. C. Ramey, J. Chem. Phys., in press.

29. R. Theimer and J. R. Nielson, J. Chem. Phys. 30, 98 (1959).

30. H. J. Bernstein and N. Sheppard, J. Chem. Phys. 37, 3012
(1962).

31. D. F. Evans, Mol. Phys. 5, 183 (1962).

32. W. G. Proctor and F. C. Yu, Phys. Rev. 78, 471 (1950).

33. W. G. Proctor and F. C. Yu, Phys. Rev. 81, 20 (1951).

34. H. S. Gutowsky, D. W. McCall, and C. P. Slichter, Phys.
Rev. 84, 589 (1951).

35. E. L. Hahn and D. E. Maxwell, Phys. Rev. 84, 1246 (1951).

36. N. F. Ramsey and E. M. Purcell, Phys. Rev. 85, 143 (1952).

37. M. Karplus, Bull. Am. Phys. Soc. Ser. II 3, 119 (1958).

38. M. Karplus and D. H. Anderson, J. Chem. Phys. 30, 6 (1959).

































APPENDIX















APPENDIX

Theory of Nuclear Spin-Spin Coupling


An additional type of fine structure distinguishable

from that due to different chemical shifts was first observed

by Proctor and Yu (32,33) in 1950. The chemical shift arises

when a molecule possesses several magnetic nuclei in different

electronic environments and is dependent upon the externally

applied field. Gutowsky, McCall,and Slichter (34) and Hahn

and Maxwell (35) independently postulated that this extra fine

structure was due to the interaction of the magnetic moments

that was being transmitted via the orbital magnetic moments of

the molecular electrons. However, Ramsey and Purcell (36) showed

that this type of an interaction could account for only a small

fraction of the observed values and instead suggested that the

mechanism was that of the exchange-coupled spin magnetic moments

of the molecular electrons. PThe calculated values of the coupling

constants for this type of interaction are in fair agreement with

the observed values. The calculations are somewhat complex and a

complete analysis has been performed only on a limited number of

simple compounds.

The following discussion is taken in part from the work

of Ramsey and Purcell (36) who developed the first successful

general theory of nuclear spin-spin coupling and from the work

84








of Karplus and co-workers (25,37,38) who applied the valence

bond theory to the approximate second-order perturbation method

of Ramsey.

The Hamiltonian for the motion of the electrons in the

vicinity of nuclei which possesses magnetic moments has two

parts which involve the nuclear spin vector I-,

The first term represents the dipole-dipole interaction

between the nuclear and electronic magnetic moments. Sk is

the electron spin vector, 7n is the magnetogyric ratio of

nucleus n and rkn is rk-rn.


U 3(Sk rkh)(Inrkn) (SkIn)
I = c zk Zn 7n L 5 3r
rkn rkn


The second term


H2 = c' E E 7n 6(rkn)(SkIn)


depends upon the property of the electron at rk = 0 and is

usually referred to as the contact term.

As expected the contact term gives the principal contribution

to the coupling constant between protons since the electrons on a

hydrogen atom are well represented by a Is type atomic orbital.

Most of the theoretical work that has been accomplished

to date concerns only the contact term which seems to account

for about 90 per cent of the proton-proton coupling in a number

of cases. The application of the valence bond theory (37) in

relating the coupling constant to the molecular geometry of









hydrocarbons has proved quite useful. The relationship of

JHHT to the dihedral angle 0 as derived from the above theory is


8.5 cos2e 0.28 00o~---E 900
JHH'(contact) =
9.5 cos 9 0.28 900o0Gi_1800


These equations seem to be in fair agreement with the experimental

results.

Theoretical calculations of F-H and F-F coupling constants

are very complicated indeed, and as yet no significant results

have been published. Karplus extended the above relationship of

the coupling constant to the dihedral angle by assuming that

0F = 2 or 36H. This rather gross approximation is based on the

e.p.r. hyperfine splitting in a fluorine containing aromatic

free radical and the n.m.r. hyperfine splitting in some fluoro-

benzenes. The agreement between the theoretical and experimental

values indicates that the contact electron spin term is the major

factor in most of the observed couplings in olefins, however, the

agreement is only in the order magnitude.

Actually, the situation regarding F-F and F-H coupling

is rather complex. The theoretical calculations must await the

experimental evidence as to the mechanism or the degree of each

mechanism of the coupling. The use of the experimental results

in an effective manner must await the theoretical calculations

on the contribution of the electron orbital and the dipolar

electron-spin terms.















BIOGRAPHICAL SKETCH


Kermit Cecil Ramey was born in Elkhorn City, Kentucky,

on March 25, 1932. He attended a number of public schools in

Pike County, Kentucky, and in July, 1949, he entered the United

States Army and served until September, 1952. He entered Eastern

Kentucky State College at Richmond, Kentucky, in 1954, and received

a Bachelor of Science Degree in Chemistry. He then entered the

University of Kentucky and received the Master of Science Degree

in June, 1960.

Mr. Ramey entered the Graduate School of the University

of Florida in September, 1960, as a graduate assistant. From

September, 1960, until the present time he has worked as a

teaching and research assistant.

Mr. Ramey is married to the former Beverly D. Earlywine

and is the father of two children. He is a member of Sigma Xi

and the American Chemical Society.













This dissertation was prepared under the direction of

the chairman of the candidate's supervisory committee and has

been approved by all members of that committee. It was submitted

to the Dean of the College of Arts and Sciences and to the

Graduate Council, and was approved as partial fulfillment of the

requirements for the degree of Doctor of Philosophy.


June 20, 1963



Dean, College of Arts a'd Sciences



Dean, Graduate School

Supervisory Committee:



Chairman




I "C^-










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AUTHOR: Ramey, Kermit
TITLE: Nuclear spin-spin coupling in fluorocarbon derivatives. (record number:
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PUBLICATION DATE: 1963


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