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The microwave spectrum and 35Cl nuclear quadrupole coupling in chlorotrifluoroethylene
JOURiVdL
OF MOLECULAR
SPECTROSCOPY
33, 233-241 (1269)
The Microwave Spectrum and 35CI Nuclear Coupling in Chlorotrifluoroethylene R. G. STONE Noyes
Chemical Laboratory,
AND
Quadrupole
W. H. FLYGARE
University
of Illinois,
Urbana, Illinois
61801
The microwave spectrum of F&=:CFW!l was observed in the 8-26 GHe frequency range. The rotational constants are (MHz): A = 4506.05 f 0.02; B = 2268.66 f 0.02; and C = 1508.02 f 0.01. The Wl quadrupole coupling constants along the appropriate inertial axes are (MHz) : xc0 = -50.10 f 0.10; XW,= 1-11.36 ZIZ0.10; and xee = +38.74 & 0.20. The Wl quadrupole coupling constants in H&=CFWl were remeasured and a structure was proposed for this molecule. The coupling constants are (MHz): xao = -73.04 f 0.10; xbb = $38.60 f 0.10; and xc0 = +34.44 f 0.20. The coupling constants in both molecules were transformed into the principal field gradient axis systems and compared with quadrupole coupling constants in similar molecules. I. INTRODUCTION
The microwave spectra and 35C1nuclear quadrupole coupling constants have been measured for several substituted ethylenes (1). Substitutional changes in the quadrupole coupling constant along the carbon-chlorine bond shows that the numerical value of the coupling constant increases as the number of substituted halogen atoms increases and that fluorine has a greater effect than chlorine. However some inconsistency is present, as the coupling constant in 1 , 1-dichloroethylene (2) is numerically larger than 1-chloro-1-fluoroethylene (3). These data suggest that the coupling constant in a tetrahaloethylene will increase, but the amount of increase is somewhat uncertain. The present work was initiated to determine the quadrupole coupling constants in chlorotrifluoroethylene and I-chloro-1-fluoroethylene to see if the coupling constants are consistent with previous results on the haloethylenes, and to resolve the seemingly inconsistent results on the 1, I-dihaloethylenes. Structures for chlorotrifluoroethylene and I-chloro-1-fluoroethylene were also determined which are generally consistent with known effects of halogen substitution on ethylene (4). II. EXPERIMENTAL The microwave
spectrograph
METHODS
used in this work has been described
(5, 6;)’ 233
elsewhere
STONE
234
AND
FLYGARE
A. Chlorotrijluoroethykne 1. Spectrum,
Assignment, and Rotational Constants. A sample of chlorotrifluoroethylene was obtained from the Matheson Co., Inc., Joliet, Illinois, and was used without further purification. A preliminary calculation of the rotational constants indicated that the dipole moment would be more closely aligned with the b principal inertial axis, and thus a spectrum exhibiting b-dipole selection rules would be observed. The dipole moment of chlorotrifluoroethylene has been obtained from measurements of the gas phase dielectric constant and the values obtained are about 0.40 (7-9). The spectrum was thus expected to be composed of weak transitions. A search for Q-branch transitions of the 35C1isotopic species was made in the 8-26 GHz region, and a partial assignment was obtained by plotting (A - C)/2 vs. K for several of the observed Q-branch transitions. The complete assignment was obtained by measuring R-branch transitions and making a least squares fit of all measured transitions. The results of the fit give the rotational constants TABLE
I
ROTATIONAL CONSTANTS FOR FzC=CF3%1 AND H&=CFWI The calculated values were obtained from the structures in Tables IV and VI. Calculated
Observed
F&=CFWl I, lb I,
zi
B c
111.987 amu bz 223.162 amu AZ 335.151 amu LIZ -0.49636 4514.20 MHz. 2265.31 MHz 1508.37 MHz
112.189 222.832 335.213 -0.49261 4506.05” 2268.66” 1508.09”
amu liz amu Ag amu _kz MHz MHz MHz
A = +0.192 H&=CFWI Observedb
I, zb
a ltO.02 MHz. b Ref. (3).
47.377 amu i%z 47.327 amu bz 98.884 amu hz 99.082 amu AZ 146.261 amu AZ 146.600 amu 82 - 0.54089 -0.542724 10 670.33 MHz 10 681.62 MHz 5112.37 MHz 5102.17 MHz 3456.36 MHz 3448.38 MHz A = $0.191
CXfLOROTRIFLUOROETHYLENE
235
listed in Table I. The experimental and calculated frequencies of the rigid rotor transitions are listed in Table II. No u-dipole transitions were observed. 2. Nuclear Quadrupole Coupling. The first-order quadrupole coupling analysis follows methods discussed previously (6, 10). In chlorotrifluoroethylene, the quadrupole coupling constants were obtained from a statistical analysis of a large number of Q-branch transitions since no low J transitions were observed. The resulting quadrupole coupling constants are given in Table III. Although calculations revealed that a fen- rotational states were nearly degenerate, the transitions involving these energy levels were too weak to be observed and the complete nuclear quadrupole coupling tensor could not be obtained. The quadrupole coupling constants in the field gradient axis system lvere obtained by assuming that the C-Cl bond axis was coincident with one of the principal field gradient axes (I). The angle of rotation between the inertial axes and the bond axis system was thus determined by an assumed structure. The resultant bond-axis quadrupole coupling constants are also listed in Table III. The assumed structure, from which the calculated moments of inertia in Table I were obtained, is listed in Table IV and shown in Fig. 1. Originally, the assumed structure was composed of the structure of l,l-difluoro-%-chloroethylene (1) with a C-F3 bond length of 1.323 A and a C1= C&F3 angle of 125”. This structure gave rotational constants quite close to the experimental rotational constants and only minor changes were needed to fit the experimental rotational constants. B. I-Chloro-1 -JEuoroethybize A sample of 1-chloro-1-fluoroethylene was obtained from Pierce Chemical Co., Rockford, Illinois, and was used without further purification. The 35C1 nuclear quadrupole coupling constants were redetermined by measuring the OoO--+ 111 and 10~---+ 212 transitions. These values were checked by measuring the 312 + 3?i transition. The coupling constants are listed in Table III and the calculated frequencies of the rigid rotor transitions are listed in Table V. The rotational constants used in the calculation were obtained by Bragg ef al. (3). The quadrupole coupling constants in the field gradient axis system, listed in Table III were obtained in the same manner as in chlorotrifluoroethylene, and the angle of rotation between the inertial axis system and the C-Cl bond axis was determined from an assumed structure. The assumed structure is listed in Table VI and shown in Fig. 2. This structure was originally the same as the structure of 1 , 1-diffuoroethylene (4) with a C-Cl bond length of 1.720 A and Cl = C&Cl angle of 124.5”. The changes in this structure which were required to fit the experimental rotational constants were mainly a lengthening of the CT-F bond distance to 1.325 s and a decrease in the C1= C!-F angle to 123.9”. These are compared to 1.323 8 and 125.4”
STONE
236
AND
FLYGARE
TABLE
II
AND CALCULATED SPECTRUMOF F#Z=CFWl The rotational constants are in Table I and the quadrupole coupling constants are in Table III. All frequencies are in MHz. OBSERVED
Transition 202 -+ 3oa
F + F’ l/2
--f 3/2
7/2 -+ 9/2 5/2 3/Z --t -+ 7/2 5/2 :
v(expt.)
11 733.85
vo(expt1.) 11 736.38
&calc.) 11 736.38
11 737.13
(Y - vo) (exptl.)
(v - uo) (talc.)
-2.70
-2.73 -2.60
$0.58
+0.58 +0.71
422 -+ 491
512 1112 7/2 912
-+ -+ -+ --t
512 11/2 7/2 9/2
11 641.74 11 644.51 11.649.66 11 652.44
11 647.39
11 647.36
-5.65 -2.88 $2.27 $5.05
-5.68 -5.89 $2.28 $5.06
523 -+ 532
7/2 13/2 9/2 11/a
--t + -+ --f
712 1312 912 11/2
10 10 10 10
671.20 677.52 680.94 682.36
10 679.35
10 679.34
-3.15 -1.83 +1.59 +3.01
-3.18 -1.84 +1.59 +2.94
19 803.46
19 804.16
19 804.20
-0.70 -0.17 +0.48
-0.66 -0.13 -0.08 +0.45
506 ---f 616
912 --f 11/2 7/2 +
9/2
11/2 -+ 13/2 1 13/2 ---f 15/2
19 803.99 19 804.64
624 -+ 63s
9/2 1512 11/2 13/2
-+ + --) -+
9/2 15/2 11/a 1312
9911.32 9912.06 9914.53 9915.26
9913.35
9913.37
-2.03 -1.29 $1.18 $1.91
-2.04 -1.28 +1.17 +1.93
61s +
9/2 15/2 11/2 13/2
--t + -+ --f
912 15/2 11/2 1312
9041.54 9042.44 9045.22 9046.10
9043.90
9043.65
-2.36 -1.45 $1.32 +2.20
-2.34 -1.47 +1.33 +2.20
11/2 1712 13/2 15/2
--f + 4 +
u/2 17/2 1312 15/2
9757.25 9757.75 9759.78 9760.28
9758.80
9758.74
-1.55 -1.05 +0.98 +1.48
-1.56 -1.05 +0.98 +1.49
15/2 2112 17/2 19/2
-+ ---) + -+
15/2 21/2 1712 19/2
13 13 13 13
158.64 158.95 160.58 160.90
13 159.78
13 159.77
-1.14 -0.83 +0.80 +1.12
-1.18 -0.86 +0.82 +1.15
15/2 21/2 17/2 19/2
+ -+ + +
15/2 21/2 17/2 19/2
12 12 12 12
322.61 322.98 325.03 325.40
12 324.03
12 323.99
-1.42 -1.05 +1.00 +1.37
-1.37 -1.00 +0.96 +1.33
624
CHLOROTRIFLUOROETHYLENE TABLE Transition
F -+ F’
237
II-Continued
dexpt.)
vo(exptl.)
vo(calc.j
(v - Y”) (v -
V”)
iexpti.)
(talc.)
104s+ 1055
1712 23/2 19/a 2112
4 -+ -+ --f
17/2 2312 19/2 21/2
19 19 19 19
244.87 245.14 246.05 247.34
19 246.11
19 246.30
-1.24 -0.97 +0.71 +1.23
-1.29 -0.96 +0.71 +1.26
1031+
17/2 23/2 1912 21/2
+ --f --) --f
17/2 23/2 1912 21/2
12 12 12 12
833.21 833.45 834.90 835.14
12 834.19
12 824.22
-0.98 -0.74
-0.97 -0.73
+0.71 +0.95
+0.71 +0.95
19/2 25/2 2112 23/2
---f + -+ -+
19/2 25/2 21/z 23/2
13 13 13 13
558.36 558.56 560.01 560.23
13 559.29
-0.93 -0.73 f0.72 f0.94
-0.95 -0.73 +0.72 +0.93
lO*s
1138 ---) 1147
TABLE QUADRUPOLE All values
COUPLING
CONSTANTS
13 559.50
III FOR F&=CFWl
AND
H2C=CFWI
are in MHz. Principal inertial axis system
Principal field gradient axis system F&=CFWl
x=a = xbb = xcc =
-50.10 +11.36 +38.74
f f f
0.10 0.10 0.20
XM = x&3 = xyy =
-89.14 +50.40 f38.74
XUU = x8@ = X 'Iy=
$38.98 $34.44
H#=CFWl Xao = -73.04 Xbb = +38.60 Xcc = f34.44
f f f
0.10 0.10 0.20
TABLE ASSUMED
STRUCTURE
IV
FOR CHLOROTRIFLUOROETHYLENE
c1=c2
Cl-F1 CrFt
Cz-Fs G-Cl L CL=Cr-FI L C~=CI--F~ L C I=C z--F3 LC1=C2-Cl
-73.42
see (Fig. 1) 1.310 1.328 1.323 1.328 1.700
;i g ;i il i
123”36’ 125”O’ 124”30’ 123”2O’
STONE
235
AND
FLYGARE
in 1, I-difluoroethylene. The rotational constants were relatively insensitive to the Cl= G-Cl angle, and changing the angle produces only a very small change in the angle between the A inertial axis and the C-Cl bond. Even though this angle is not known very accurately, it will have only very small effect in
FIG. 1. Structure trifluoroethylene.
(see Table
IV) and orientation
TABLE
OBSERVED AND CALCULATED The quadrupole Transition
coupling F + F’
constants
3/z + l/2 312 + 5/2 312 -+ 312
14 120.40 14 128.17 14 137.76
l/2
21 008.30
101 + 212
vo(expt1.)
vo(calc.)
14 130.11
14 130.00
21 026.54 4
312
312 4
l/2) 7/2 512 312
21 025.34 21 035.02 21 041.16
3/2 9/2 5/2 7/2
+ --) 4 +
3/2 9/2 512 7/2
15 15 15 15
321
15 989.96 979.75 985.65 992.55 998.41
(v - Y0) (exptl.)
(v - m) (talc.)
-9.71 -1.94 $7.65
-9.65 -1.93 $7.72
-18.24
-18.26
-9.70
21 016.84 + -+ -+ 4
are in MHz.
21 026.76
5;2 ---f 5j2 l/2 5/2 3/2 312
axis in chloro-
OF H&=CFWl
III. All frequencies
-. 000+ 111
inertial
V SPECTRUM
are in Table
v(expt1.j
of the principal
-9.80 -9.65
-1.20 _t8.48 +14.62
-1.19 +8.46 +14.61
-10.21 -4.31 +2.59 +s.45
-10.20 -4.24 +2.55 +s.49
15 989.95
CHLOROTRIFLUOROETHYLEXE TABLE
239
VI
ASSUMED STRUCTURE FOR 1-CHLORO-1-FLIJO~OIWHYLENE (see Fig. 2) 1.315 1.079 1.079 1.325 1.725
c1=ce
CL-HI C&Hz C2-F c&Cl
120.0”
L C&=C~--HI L C+&-H2 L Cl=Cz-F LCFCr-Cl
120.0” 123.9” 124.5”
FIG. 2. Structure 1-fluoroethylene.
(see Table VI) and orientation
determining axis system.
nuclear
the
‘4 lx ;i ;i ;i
quadrupole III.
of the principal
coupling
constants
inertial axis in l-chloro-
in the field gradient
DISCUSSION
A comparison of nuclear quadrupole coupling constants in the field gradient axis system in halogen substituted ethylenes is given in Table VII. The coupling constant along the C-Cl bond in chlorotrifluoroethylene, -89.14 MHz, is considerably larger than any of the other substituted ethylenes. The increase in the coupling constant when a fluorine atom is substituted for the hydrogen in 1, I-difluoro-2-chloroethylene is much larger than indicated by the difference in coupling constants in chloroethylene and 1-chloro-1-fluoroethylene. Tetrachloroethylene has been studied by nuclear quadrupole resonance spec-
STONE
240
AND
FLYGARE
troscopy, and has a resonance at 38.6 MHz (14). As solid phase coupling constants are approximately 10 % lower than gas phase coupling constants, the corresponding coupling constant for gaseous tetrachloroethylene would be about -85 MHz. Since fluorine substitution has a greater effect on 35C1coupling constants than chlorine substitution, the value obtained in chlorotriffuoroethylene appears reasonable. Structural information and 35C1nuclear quadrupole coupling constants in various molecules indicate that replacement of an atom by a more electronegative atom increases the s-character in the other bonds of the atom to which the new group is bonded. This effect is reduced as the substitution occurs further away from the atom bonded to the chlorine (14, 15). The effect of the increase in s-character of a carbon atom bonded to a chlorine atom effectively increases the electronegativity of the carbon atom and decreases the ionic character in TABLE
VII
PRINCIPAL ELEMENTS IN THE 36C1 NUCLEAR &UADRUPOLE COUPLING CONSTANT TENSOR IN THB FIELD GRADIENT AXIS SYSTEM FOR SUBSTITUTED ETHYLENES X=a is along the C-Cl bond and XBBis in the molecular plane. All values are in MHz. Molecule H ,C=CHCl cis-FHC=CHCl F&=CHCl F&=CFCl cis-CICH=CHCl H&=CClz H&=CFCl g
XBB -70.16 -73.7 -77.40 -89.14 -72.3 -78.70 -73.42
$40.07 +40.3 +40.64 $50.40 +40.4 f43.58 $38.98
TABLE
Ref.
XYY f30.09 +33.4 +36.76 +3s.74 +31.9 +35.12 34.44
(13) (12) (1) Present work (11) (2) Present work
VIII
FRACTIONAL CONTRIBUTION OF PARTIAL STRUCTURES TO THE C-Cl SUBSTITUTED ETHYLENES Values are obtained
from the 36Cl quadrupole
coupling constants
Covalent chagter Molecule
‘CL /
H&=CHCl cis-HFC=CHCl F&=CHCl FaC=CFCl cis-HClC=CHCl H,C=CClz HzC=CFCl
\ 0.753 0.791 0.831 0.914 0.776 0.845 0.788
Ionic character Cl\ c=c+ / \ 0.194 0.173 0.149 0.024 0.179 0.110 0.188
BOND IN
in Table VII. Double-bond character Clf
\
/
c--c 0.053 0.036 0.020 0.062 0.045 0.045 0.024
/
\
“II
CHLOROTRIFLUOROETHYLENE
the bond to the chlorine atom. This is apparently what happens in the halogensubstituted ethylenes. All relative changes in the coupling constants given in Table V are consistent with this reasoning except for 1-chloro-1-fluoroethylene. The effect of fluorine substitution on the same carbon to which the chlorine is bonded should be considerably greater than substitution on the other carbon atom. This large effect is exhibited by 1, 1-dichloroethylene and chlorotrifluoroethylene. From the relative changes in the coupling constant with substitution in various positions, xaa in I-fluoro-I-chloroethylene would be expected to be around -80 to -83 MHz. Table VIII lists calculated covalent, ionic, and double-bond contributions to the carbon-chlorine bond. The double-bond character or contribution of the C-C= Cl+ structure to the C-Cl bond was calculated from the asymmetry in the field gradient perpendicular to the C-Cl bond axis. The covalent character was calculated assuming 15 % s-character and no d-character in the Gbonding orbital of the chlorine atom. The ionic contribution completes the C-Cl bond (1, 10). ACKNOWLKDGMENT The support
of the National
RECEIVED: March
Science
Foundation
is gratefully
acknowledged.
15, 1969 REFERENCES
1. 9. 3. 4. 6.
R. G. STONE AND W. H. FLYGARE, J. Chem. Phys. 49, 1943 (1968). S. SEKINO .&NDT. NISHIKAWA, J. Phys. Sec. Japan la,43 (1957). J. K. BR.~GG, T. C. MADISON, AND A. H. SHARBAUGH, Phys. Rev. 77, 148 (1950). V. W. LAURIE AND D. T. PENCE, J. Chem. Phys. 38,2693 (1963). W. H. FLYGARE, J. Chem. Phys. 41, 206 (1964). 6. M. L. UNLAND, V. W. WEISS, AND W. H. FLYG‘IRE, J. Chem. Phys. 42, 2138 (1965).
7. M. T. ROGERS AND II. D. PRUCT, J. Am. Chem. Sot. 77, 3686 (1955). 8. A. Dr GIACOMO AND C. P. SMYTH, J. Am. Chem. Sot. 77, 774 (1955). 9. J. E. BOGGS, C. M. CRAIN, AND J. E. WHITEFORD, J. Phys. Chem. 61, 482 (1957). 10. C. H. TOWNES AND A. L. SCHAWLOW, “Microwave Spectroscopy.” McGraw-Hill, York, 1955. 11. W. H. FLYG~R~ AND J. A. HOWE:, J. Chem. Phys. 36,440 (1962). 1.2. J. A. Howe, J. Chem. Phys. 34, 1247 (1961). 19. 1~. KIVELSON, E. B. WILSON, AND D. It. LIDE, J. Chem. Phys. 32, 205 (1960). 14. H. 0. HOOP~B AND P. J. BRAY, J. Chem. Phys. 33, 334 (1960). 15. H. A. BKNT, J. Chem. Phys. 33, 1259 (1960).
New
OF MOLECULAR
SPECTROSCOPY
33, 233-241 (1269)
The Microwave Spectrum and 35CI Nuclear Coupling in Chlorotrifluoroethylene R. G. STONE Noyes
Chemical Laboratory,
AND
Quadrupole
W. H. FLYGARE
University
of Illinois,
Urbana, Illinois
61801
The microwave spectrum of F&=:CFW!l was observed in the 8-26 GHe frequency range. The rotational constants are (MHz): A = 4506.05 f 0.02; B = 2268.66 f 0.02; and C = 1508.02 f 0.01. The Wl quadrupole coupling constants along the appropriate inertial axes are (MHz) : xc0 = -50.10 f 0.10; XW,= 1-11.36 ZIZ0.10; and xee = +38.74 & 0.20. The Wl quadrupole coupling constants in H&=CFWl were remeasured and a structure was proposed for this molecule. The coupling constants are (MHz): xao = -73.04 f 0.10; xbb = $38.60 f 0.10; and xc0 = +34.44 f 0.20. The coupling constants in both molecules were transformed into the principal field gradient axis systems and compared with quadrupole coupling constants in similar molecules. I. INTRODUCTION
The microwave spectra and 35C1nuclear quadrupole coupling constants have been measured for several substituted ethylenes (1). Substitutional changes in the quadrupole coupling constant along the carbon-chlorine bond shows that the numerical value of the coupling constant increases as the number of substituted halogen atoms increases and that fluorine has a greater effect than chlorine. However some inconsistency is present, as the coupling constant in 1 , 1-dichloroethylene (2) is numerically larger than 1-chloro-1-fluoroethylene (3). These data suggest that the coupling constant in a tetrahaloethylene will increase, but the amount of increase is somewhat uncertain. The present work was initiated to determine the quadrupole coupling constants in chlorotrifluoroethylene and I-chloro-1-fluoroethylene to see if the coupling constants are consistent with previous results on the haloethylenes, and to resolve the seemingly inconsistent results on the 1, I-dihaloethylenes. Structures for chlorotrifluoroethylene and I-chloro-1-fluoroethylene were also determined which are generally consistent with known effects of halogen substitution on ethylene (4). II. EXPERIMENTAL The microwave
spectrograph
METHODS
used in this work has been described
(5, 6;)’ 233
elsewhere
STONE
234
AND
FLYGARE
A. Chlorotrijluoroethykne 1. Spectrum,
Assignment, and Rotational Constants. A sample of chlorotrifluoroethylene was obtained from the Matheson Co., Inc., Joliet, Illinois, and was used without further purification. A preliminary calculation of the rotational constants indicated that the dipole moment would be more closely aligned with the b principal inertial axis, and thus a spectrum exhibiting b-dipole selection rules would be observed. The dipole moment of chlorotrifluoroethylene has been obtained from measurements of the gas phase dielectric constant and the values obtained are about 0.40 (7-9). The spectrum was thus expected to be composed of weak transitions. A search for Q-branch transitions of the 35C1isotopic species was made in the 8-26 GHz region, and a partial assignment was obtained by plotting (A - C)/2 vs. K for several of the observed Q-branch transitions. The complete assignment was obtained by measuring R-branch transitions and making a least squares fit of all measured transitions. The results of the fit give the rotational constants TABLE
I
ROTATIONAL CONSTANTS FOR FzC=CF3%1 AND H&=CFWI The calculated values were obtained from the structures in Tables IV and VI. Calculated
Observed
F&=CFWl I, lb I,
zi
B c
111.987 amu bz 223.162 amu AZ 335.151 amu LIZ -0.49636 4514.20 MHz. 2265.31 MHz 1508.37 MHz
112.189 222.832 335.213 -0.49261 4506.05” 2268.66” 1508.09”
amu liz amu Ag amu _kz MHz MHz MHz
A = +0.192 H&=CFWI Observedb
I, zb
a ltO.02 MHz. b Ref. (3).
47.377 amu i%z 47.327 amu bz 98.884 amu hz 99.082 amu AZ 146.261 amu AZ 146.600 amu 82 - 0.54089 -0.542724 10 670.33 MHz 10 681.62 MHz 5112.37 MHz 5102.17 MHz 3456.36 MHz 3448.38 MHz A = $0.191
CXfLOROTRIFLUOROETHYLENE
235
listed in Table I. The experimental and calculated frequencies of the rigid rotor transitions are listed in Table II. No u-dipole transitions were observed. 2. Nuclear Quadrupole Coupling. The first-order quadrupole coupling analysis follows methods discussed previously (6, 10). In chlorotrifluoroethylene, the quadrupole coupling constants were obtained from a statistical analysis of a large number of Q-branch transitions since no low J transitions were observed. The resulting quadrupole coupling constants are given in Table III. Although calculations revealed that a fen- rotational states were nearly degenerate, the transitions involving these energy levels were too weak to be observed and the complete nuclear quadrupole coupling tensor could not be obtained. The quadrupole coupling constants in the field gradient axis system lvere obtained by assuming that the C-Cl bond axis was coincident with one of the principal field gradient axes (I). The angle of rotation between the inertial axes and the bond axis system was thus determined by an assumed structure. The resultant bond-axis quadrupole coupling constants are also listed in Table III. The assumed structure, from which the calculated moments of inertia in Table I were obtained, is listed in Table IV and shown in Fig. 1. Originally, the assumed structure was composed of the structure of l,l-difluoro-%-chloroethylene (1) with a C-F3 bond length of 1.323 A and a C1= C&F3 angle of 125”. This structure gave rotational constants quite close to the experimental rotational constants and only minor changes were needed to fit the experimental rotational constants. B. I-Chloro-1 -JEuoroethybize A sample of 1-chloro-1-fluoroethylene was obtained from Pierce Chemical Co., Rockford, Illinois, and was used without further purification. The 35C1 nuclear quadrupole coupling constants were redetermined by measuring the OoO--+ 111 and 10~---+ 212 transitions. These values were checked by measuring the 312 + 3?i transition. The coupling constants are listed in Table III and the calculated frequencies of the rigid rotor transitions are listed in Table V. The rotational constants used in the calculation were obtained by Bragg ef al. (3). The quadrupole coupling constants in the field gradient axis system, listed in Table III were obtained in the same manner as in chlorotrifluoroethylene, and the angle of rotation between the inertial axis system and the C-Cl bond axis was determined from an assumed structure. The assumed structure is listed in Table VI and shown in Fig. 2. This structure was originally the same as the structure of 1 , 1-diffuoroethylene (4) with a C-Cl bond length of 1.720 A and Cl = C&Cl angle of 124.5”. The changes in this structure which were required to fit the experimental rotational constants were mainly a lengthening of the CT-F bond distance to 1.325 s and a decrease in the C1= C!-F angle to 123.9”. These are compared to 1.323 8 and 125.4”
STONE
236
AND
FLYGARE
TABLE
II
AND CALCULATED SPECTRUMOF F#Z=CFWl The rotational constants are in Table I and the quadrupole coupling constants are in Table III. All frequencies are in MHz. OBSERVED
Transition 202 -+ 3oa
F + F’ l/2
--f 3/2
7/2 -+ 9/2 5/2 3/Z --t -+ 7/2 5/2 :
v(expt.)
11 733.85
vo(expt1.) 11 736.38
&calc.) 11 736.38
11 737.13
(Y - vo) (exptl.)
(v - uo) (talc.)
-2.70
-2.73 -2.60
$0.58
+0.58 +0.71
422 -+ 491
512 1112 7/2 912
-+ -+ -+ --t
512 11/2 7/2 9/2
11 641.74 11 644.51 11.649.66 11 652.44
11 647.39
11 647.36
-5.65 -2.88 $2.27 $5.05
-5.68 -5.89 $2.28 $5.06
523 -+ 532
7/2 13/2 9/2 11/a
--t + -+ --f
712 1312 912 11/2
10 10 10 10
671.20 677.52 680.94 682.36
10 679.35
10 679.34
-3.15 -1.83 +1.59 +3.01
-3.18 -1.84 +1.59 +2.94
19 803.46
19 804.16
19 804.20
-0.70 -0.17 +0.48
-0.66 -0.13 -0.08 +0.45
506 ---f 616
912 --f 11/2 7/2 +
9/2
11/2 -+ 13/2 1 13/2 ---f 15/2
19 803.99 19 804.64
624 -+ 63s
9/2 1512 11/2 13/2
-+ + --) -+
9/2 15/2 11/a 1312
9911.32 9912.06 9914.53 9915.26
9913.35
9913.37
-2.03 -1.29 $1.18 $1.91
-2.04 -1.28 +1.17 +1.93
61s +
9/2 15/2 11/2 13/2
--t + -+ --f
912 15/2 11/2 1312
9041.54 9042.44 9045.22 9046.10
9043.90
9043.65
-2.36 -1.45 $1.32 +2.20
-2.34 -1.47 +1.33 +2.20
11/2 1712 13/2 15/2
--f + 4 +
u/2 17/2 1312 15/2
9757.25 9757.75 9759.78 9760.28
9758.80
9758.74
-1.55 -1.05 +0.98 +1.48
-1.56 -1.05 +0.98 +1.49
15/2 2112 17/2 19/2
-+ ---) + -+
15/2 21/2 1712 19/2
13 13 13 13
158.64 158.95 160.58 160.90
13 159.78
13 159.77
-1.14 -0.83 +0.80 +1.12
-1.18 -0.86 +0.82 +1.15
15/2 21/2 17/2 19/2
+ -+ + +
15/2 21/2 17/2 19/2
12 12 12 12
322.61 322.98 325.03 325.40
12 324.03
12 323.99
-1.42 -1.05 +1.00 +1.37
-1.37 -1.00 +0.96 +1.33
624
CHLOROTRIFLUOROETHYLENE TABLE Transition
F -+ F’
237
II-Continued
dexpt.)
vo(exptl.)
vo(calc.j
(v - Y”) (v -
V”)
iexpti.)
(talc.)
104s+ 1055
1712 23/2 19/a 2112
4 -+ -+ --f
17/2 2312 19/2 21/2
19 19 19 19
244.87 245.14 246.05 247.34
19 246.11
19 246.30
-1.24 -0.97 +0.71 +1.23
-1.29 -0.96 +0.71 +1.26
1031+
17/2 23/2 1912 21/2
+ --f --) --f
17/2 23/2 1912 21/2
12 12 12 12
833.21 833.45 834.90 835.14
12 834.19
12 824.22
-0.98 -0.74
-0.97 -0.73
+0.71 +0.95
+0.71 +0.95
19/2 25/2 2112 23/2
---f + -+ -+
19/2 25/2 21/z 23/2
13 13 13 13
558.36 558.56 560.01 560.23
13 559.29
-0.93 -0.73 f0.72 f0.94
-0.95 -0.73 +0.72 +0.93
lO*s
1138 ---) 1147
TABLE QUADRUPOLE All values
COUPLING
CONSTANTS
13 559.50
III FOR F&=CFWl
AND
H2C=CFWI
are in MHz. Principal inertial axis system
Principal field gradient axis system F&=CFWl
x=a = xbb = xcc =
-50.10 +11.36 +38.74
f f f
0.10 0.10 0.20
XM = x&3 = xyy =
-89.14 +50.40 f38.74
XUU = x8@ = X 'Iy=
$38.98 $34.44
H#=CFWl Xao = -73.04 Xbb = +38.60 Xcc = f34.44
f f f
0.10 0.10 0.20
TABLE ASSUMED
STRUCTURE
IV
FOR CHLOROTRIFLUOROETHYLENE
c1=c2
Cl-F1 CrFt
Cz-Fs G-Cl L CL=Cr-FI L C~=CI--F~ L C I=C z--F3 LC1=C2-Cl
-73.42
see (Fig. 1) 1.310 1.328 1.323 1.328 1.700
;i g ;i il i
123”36’ 125”O’ 124”30’ 123”2O’
STONE
235
AND
FLYGARE
in 1, I-difluoroethylene. The rotational constants were relatively insensitive to the Cl= G-Cl angle, and changing the angle produces only a very small change in the angle between the A inertial axis and the C-Cl bond. Even though this angle is not known very accurately, it will have only very small effect in
FIG. 1. Structure trifluoroethylene.
(see Table
IV) and orientation
TABLE
OBSERVED AND CALCULATED The quadrupole Transition
coupling F + F’
constants
3/z + l/2 312 + 5/2 312 -+ 312
14 120.40 14 128.17 14 137.76
l/2
21 008.30
101 + 212
vo(expt1.)
vo(calc.)
14 130.11
14 130.00
21 026.54 4
312
312 4
l/2) 7/2 512 312
21 025.34 21 035.02 21 041.16
3/2 9/2 5/2 7/2
+ --) 4 +
3/2 9/2 512 7/2
15 15 15 15
321
15 989.96 979.75 985.65 992.55 998.41
(v - Y0) (exptl.)
(v - m) (talc.)
-9.71 -1.94 $7.65
-9.65 -1.93 $7.72
-18.24
-18.26
-9.70
21 016.84 + -+ -+ 4
are in MHz.
21 026.76
5;2 ---f 5j2 l/2 5/2 3/2 312
axis in chloro-
OF H&=CFWl
III. All frequencies
-. 000+ 111
inertial
V SPECTRUM
are in Table
v(expt1.j
of the principal
-9.80 -9.65
-1.20 _t8.48 +14.62
-1.19 +8.46 +14.61
-10.21 -4.31 +2.59 +s.45
-10.20 -4.24 +2.55 +s.49
15 989.95
CHLOROTRIFLUOROETHYLEXE TABLE
239
VI
ASSUMED STRUCTURE FOR 1-CHLORO-1-FLIJO~OIWHYLENE (see Fig. 2) 1.315 1.079 1.079 1.325 1.725
c1=ce
CL-HI C&Hz C2-F c&Cl
120.0”
L C&=C~--HI L C+&-H2 L Cl=Cz-F LCFCr-Cl
120.0” 123.9” 124.5”
FIG. 2. Structure 1-fluoroethylene.
(see Table VI) and orientation
determining axis system.
nuclear
the
‘4 lx ;i ;i ;i
quadrupole III.
of the principal
coupling
constants
inertial axis in l-chloro-
in the field gradient
DISCUSSION
A comparison of nuclear quadrupole coupling constants in the field gradient axis system in halogen substituted ethylenes is given in Table VII. The coupling constant along the C-Cl bond in chlorotrifluoroethylene, -89.14 MHz, is considerably larger than any of the other substituted ethylenes. The increase in the coupling constant when a fluorine atom is substituted for the hydrogen in 1, I-difluoro-2-chloroethylene is much larger than indicated by the difference in coupling constants in chloroethylene and 1-chloro-1-fluoroethylene. Tetrachloroethylene has been studied by nuclear quadrupole resonance spec-
STONE
240
AND
FLYGARE
troscopy, and has a resonance at 38.6 MHz (14). As solid phase coupling constants are approximately 10 % lower than gas phase coupling constants, the corresponding coupling constant for gaseous tetrachloroethylene would be about -85 MHz. Since fluorine substitution has a greater effect on 35C1coupling constants than chlorine substitution, the value obtained in chlorotriffuoroethylene appears reasonable. Structural information and 35C1nuclear quadrupole coupling constants in various molecules indicate that replacement of an atom by a more electronegative atom increases the s-character in the other bonds of the atom to which the new group is bonded. This effect is reduced as the substitution occurs further away from the atom bonded to the chlorine (14, 15). The effect of the increase in s-character of a carbon atom bonded to a chlorine atom effectively increases the electronegativity of the carbon atom and decreases the ionic character in TABLE
VII
PRINCIPAL ELEMENTS IN THE 36C1 NUCLEAR &UADRUPOLE COUPLING CONSTANT TENSOR IN THB FIELD GRADIENT AXIS SYSTEM FOR SUBSTITUTED ETHYLENES X=a is along the C-Cl bond and XBBis in the molecular plane. All values are in MHz. Molecule H ,C=CHCl cis-FHC=CHCl F&=CHCl F&=CFCl cis-CICH=CHCl H&=CClz H&=CFCl g
XBB -70.16 -73.7 -77.40 -89.14 -72.3 -78.70 -73.42
$40.07 +40.3 +40.64 $50.40 +40.4 f43.58 $38.98
TABLE
Ref.
XYY f30.09 +33.4 +36.76 +3s.74 +31.9 +35.12 34.44
(13) (12) (1) Present work (11) (2) Present work
VIII
FRACTIONAL CONTRIBUTION OF PARTIAL STRUCTURES TO THE C-Cl SUBSTITUTED ETHYLENES Values are obtained
from the 36Cl quadrupole
coupling constants
Covalent chagter Molecule
‘CL /
H&=CHCl cis-HFC=CHCl F&=CHCl FaC=CFCl cis-HClC=CHCl H,C=CClz HzC=CFCl
\ 0.753 0.791 0.831 0.914 0.776 0.845 0.788
Ionic character Cl\ c=c+ / \ 0.194 0.173 0.149 0.024 0.179 0.110 0.188
BOND IN
in Table VII. Double-bond character Clf
\
/
c--c 0.053 0.036 0.020 0.062 0.045 0.045 0.024
/
\
“II
CHLOROTRIFLUOROETHYLENE
the bond to the chlorine atom. This is apparently what happens in the halogensubstituted ethylenes. All relative changes in the coupling constants given in Table V are consistent with this reasoning except for 1-chloro-1-fluoroethylene. The effect of fluorine substitution on the same carbon to which the chlorine is bonded should be considerably greater than substitution on the other carbon atom. This large effect is exhibited by 1, 1-dichloroethylene and chlorotrifluoroethylene. From the relative changes in the coupling constant with substitution in various positions, xaa in I-fluoro-I-chloroethylene would be expected to be around -80 to -83 MHz. Table VIII lists calculated covalent, ionic, and double-bond contributions to the carbon-chlorine bond. The double-bond character or contribution of the C-C= Cl+ structure to the C-Cl bond was calculated from the asymmetry in the field gradient perpendicular to the C-Cl bond axis. The covalent character was calculated assuming 15 % s-character and no d-character in the Gbonding orbital of the chlorine atom. The ionic contribution completes the C-Cl bond (1, 10). ACKNOWLKDGMENT The support
of the National
RECEIVED: March
Science
Foundation
is gratefully
acknowledged.
15, 1969 REFERENCES
1. 9. 3. 4. 6.
R. G. STONE AND W. H. FLYGARE, J. Chem. Phys. 49, 1943 (1968). S. SEKINO .&NDT. NISHIKAWA, J. Phys. Sec. Japan la,43 (1957). J. K. BR.~GG, T. C. MADISON, AND A. H. SHARBAUGH, Phys. Rev. 77, 148 (1950). V. W. LAURIE AND D. T. PENCE, J. Chem. Phys. 38,2693 (1963). W. H. FLYGARE, J. Chem. Phys. 41, 206 (1964). 6. M. L. UNLAND, V. W. WEISS, AND W. H. FLYG‘IRE, J. Chem. Phys. 42, 2138 (1965).
7. M. T. ROGERS AND II. D. PRUCT, J. Am. Chem. Sot. 77, 3686 (1955). 8. A. Dr GIACOMO AND C. P. SMYTH, J. Am. Chem. Sot. 77, 774 (1955). 9. J. E. BOGGS, C. M. CRAIN, AND J. E. WHITEFORD, J. Phys. Chem. 61, 482 (1957). 10. C. H. TOWNES AND A. L. SCHAWLOW, “Microwave Spectroscopy.” McGraw-Hill, York, 1955. 11. W. H. FLYG~R~ AND J. A. HOWE:, J. Chem. Phys. 36,440 (1962). 1.2. J. A. Howe, J. Chem. Phys. 34, 1247 (1961). 19. 1~. KIVELSON, E. B. WILSON, AND D. It. LIDE, J. Chem. Phys. 32, 205 (1960). 14. H. 0. HOOP~B AND P. J. BRAY, J. Chem. Phys. 33, 334 (1960). 15. H. A. BKNT, J. Chem. Phys. 33, 1259 (1960).
New