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An electron diffraction study of trifluoromethyl hypochlorite, CF3OCl
of Molecular Structure, 117 (1984) 311-315 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
Journal
Short Communication AN ELECTRON DIFFRACTION HYPOCHLORITE, CFsOCl
STUDY OF TRIFLUOROMETHYL
HEINZ OBERHAMMER Institut fiir Physikalische und Theoretische 7400 Tiibingen (West Germany) TARIQ
MAHMOOD
Department
and JEAN’NE
of Chemistry,
University
Chemie
der Universitct
Tiibingen,
M. SHREEVE of Idaho,
Moscow,
ID 83843
(U.S.A.)
(Received 24 November 1983)
The reaction chemistries of CF30F and CF,OCl are surprisingly different [ 1, 2]_ Since the structure of CF30F is known [3], we thought it would be possible to correlate this marked difference in chemical behaviour with variations in the structural parameters of these two compounds. This required a structure determination for CF30C1. CF30C1 was prepared using the literature method [4]. Decomposition producti formed during the transport in a stainless steel container from Idaho to Germany were pumped off at -142”C, until only traces (
o 1984
Elsevier
Science
Publishers B.V.
312
4.8
8.0
16.0
12.0
20.0
24.0
28.0 S
Fig. 1. Experimental (em-)and calculated (-)
1 .a
2.0
3.0
4.0 R
32.0 Cl/Ang.l
molecular intensities and differences.
5
0
CAngstromIl
Fig. 2. Experimental radial distribution function and difference curve.
tional amplitudes of closely spaced interatomic distances was constrained to the spectroscopic ratio (see Table I). The harmonic corrections Ar = r, - rz were incorporakd in the least squares analysis. With the above assumptions six geometric parameters and six vibrational amplitudes were refined simultaneously. Although some correlation coefficients between parameters are rather large (CF/CO = 4.82, CO/COCl = -6.61, CF/Z(CF) = 0.78, CO/Z(CF) = 4.86 and COCl/I(F.-F) = O-77), the six peaks in the radial distribution function allow an accurate and reliable determination of the geometric parameters. The results of the least squares analysis are summarized in Table 1. Values for bond lengths are converted from rz to rg. Attempts to refine the bond angles F&F, and F&F, separately (i.e. C, instead of Cfv symmetry for the CFs group) caused additional high correlations between
313 TABLE Results
1 of least squares analysis
(a) Geometric 0.1%
parameters:
error limits
Bond
rg (A)
C-F O-C O-Cl
1.325 1.365 1.679
(b) Vibrational
C-F O-C O-Cl F.-F 0 - - Ft O.-F, C..CI Cl--F, CI..F, (c) Agreement = 5.2
amplitudes:
(.-) (7, (3)
error limits
scale error of
‘a (“I
FCF COCl Tilta
109.2 112.9 3.9
(0.7) (0.5) (0.8)
are 30 values
1 (e.d.)
1.32 1.36 1.67 2.15 2.14 2.20 2.54 2.90 3.68
0.043 0.047 0.048 0.061
(4)b (4)b (5) (17)’
0.044 0.048 0.049 0.053
0.068
(17)C)
0.059
(A)
I (spectr.)
(/k)d
K(290
K) (zQd
0.0042 0.0033 0.0075 0.0044 0.0049 0.0031 0.0022 0.0003 0.0011
0.061 0.120 0.060
0.079 (12) 0.110 (6) 0.061(9)
factors
a possible
Angle
r (A)
(70)
RN
=Tilt of CF, spectroscopic
are 20 values and include
RZ,
= 9.0
group towards oxygen value, dCalculated from
lone pairs. “CRatio force field of ref. 8.
of
amplitudes
constrained
to
these two angles and the tilt angle and the refined values were equal within their standard deviations. The C-O and C-F bond lengths in CF30C1 agree within their experimental uncertainties with the corresponding values for CF30CF3 (see Table Z), whereas the oxygen bond angle in CF30C1 is about 6” smaller than in CF30CF3. The C-O bonds in both compounds are considerably shorter TABLE
2
‘=omparison
of geometric
Compound
C-O
CH,OCHSb CF,OCF ’ CH,OCld CF,OCle CF,OFf
1.410 1.369 1.389 1.365 1.395
parameters
for some
related
o-x (3) (4) (28) (7) (6)
1.674 (19) 1.679 (3) l-421(6)
compounds a Q
C-F
1.327
(2)
1.325 1.319
(3) (3)
=Oxygen bond angle. brs Values from ref. 9. ‘rg Values from ref. 11. erg Values from thk study. frs Values from ref. 3.
ref.
10.
drslr,
111.7 119.1 112.8 112.9 104.9
(4) (8) (21) (5) (6)
Values
from
314 th&in CHBOCHs. A comparison with &he structural pzameters of CHsOCl is not very helpful, since the experimental uncertainties for these parameters are rather large. The shortening of the. C-O bond in CH30CH3 upon CH3/CF3 substitution has .&en rationalized by polar effects [ 121 : the high positive net ch& of the CF9 carbon atom ,together with the negative net charge of oxygen results in an attractive polar effect and thus shortens the C-O bond in CFBOCF~ & compared to CHBOCHB. The carbon and oxygen net charges in CFBOCl will not be very qifferent from those in CFBOCFB, since the electronegativities of chlorine and the CF3 group are similar. Thus, we expect little difference in the C-O bond lengths of CFIOCFS and CFJOCl and this is confirmed by experiment_(Table 2). This rationalization implies positive net charges for chlorine, as well as for the CF3 groups. Fluorine is a stronger electron withdrawing substituent than chlorine or CF3 groups and we expect reduced electron. density at the oxygen atom in CFJOF. This, in turn, will reduce the bond strengthening due to polar effects and result in a longer C-O bond for CFBOF. The experimental value for this bond is ind&d Luger by about 0.03 A. The slightly shorter C-F bonds in CFBOF are also in agreement with this interpretation, since these bond lengths correlate with the effective electronegativity of the atom or group to which the CFJ group is bonded [12a, b] . Shortening of this bond in CF30F as compared to CF30Cl implies stronger electron withdrawing power of the OF group. Since we concluded from the variation of the C-O bond lengths a reduced electron density for the OF oxygen atom, the electron density of fluorine has to be considerably increased as compared to chlorine. An additional indication for a negatively charged fluorine atom is the small COF angle which can be rationalized as a result of electrostatic attraction between the positive.carbon, atom and fluorine. This angle is only slightly larger than the FOF angle in OF1 (103.2”) despite the much larger steric requirement of the CFJ group. This interpretation of our results is consistent with the available data and it supports the different chemical behaviour of these two compounds, resulting from a positive net charge on chlorine and a negative net charge on fluorine [13]. ACKNOWLEDGEMENTS
We acknowledge financial support by NATO National Science Foundation (CHE-8100156).
(RG. .384/83)
and the
REFERENCES 1 2 3 4
J. M. Shree-re, Adv. 1110%.Chem. Radiochem., 26 (1983) 119. K. K_ Johri and D. D. DesMarteau, J. Org. Chem., 48 (1983) 242. F. P. Diodati and L. S. Bartell, J. Mol. Struct., 8 (1971) 395. (a) G. E.- Gould, L. R. Anderson, D. E. Young and W. B. Fox, J. Am. Chem. Sot., 91 (1969) 1310. (b) C. J. Schack and W. Maya, J. Am. Chem. Sot., 91(1969) 2902.
315 er, Molecular 5 I-L oberhemm Structures by Diffraction Metho& Vol. 4, The Chemical Society, London, 1976, p. 24. 6 H. Oberhsnuner, W. Gambler and H. Willner, J. Mol. Struct., 70 (1981) 273. 7 J. Haase, Z. Naturforsch., TeiL A, 25 (1970) 936. 8 J. C. Kuo, D. D. DesMarteau, W. G. Fateley, R. M. Hammaker, C. J. Marsden and J. D. Witt, J. Raman Spectrosc., 9 (1980) 230. 9 U. Blukis, P. H. Kasai and R. J. Myers, J. Chem. Phys., 38 (1963) 2753. 10 A H. Lowrey, C. George, P. D’Antcnio and J. Karle, J. Mol. Struct, 63 (1980) 243. 11 J. S. Ridgen and S. S. Butcher, J. Chem. Phys, 40 (1964) 2109. 12 (a) V. Typke, M. Dakkouri and H. Oberhammer, J. Mol. Struck, 44 (1978) 85. (b) H. Oberhammer, J. MoL Struct., 28 (1975) 349. (c) H. Oberhammer, J. Fluorine Chem., 23 (1983) 147. 13 K. 0. Christe, J. Fluorine Chem, 22 (1983) 519.
Journal
Short Communication AN ELECTRON DIFFRACTION HYPOCHLORITE, CFsOCl
STUDY OF TRIFLUOROMETHYL
HEINZ OBERHAMMER Institut fiir Physikalische und Theoretische 7400 Tiibingen (West Germany) TARIQ
MAHMOOD
Department
and JEAN’NE
of Chemistry,
University
Chemie
der Universitct
Tiibingen,
M. SHREEVE of Idaho,
Moscow,
ID 83843
(U.S.A.)
(Received 24 November 1983)
The reaction chemistries of CF30F and CF,OCl are surprisingly different [ 1, 2]_ Since the structure of CF30F is known [3], we thought it would be possible to correlate this marked difference in chemical behaviour with variations in the structural parameters of these two compounds. This required a structure determination for CF30C1. CF30C1 was prepared using the literature method [4]. Decomposition producti formed during the transport in a stainless steel container from Idaho to Germany were pumped off at -142”C, until only traces (
o 1984
Elsevier
Science
Publishers B.V.
312
4.8
8.0
16.0
12.0
20.0
24.0
28.0 S
Fig. 1. Experimental (em-)and calculated (-)
1 .a
2.0
3.0
4.0 R
32.0 Cl/Ang.l
molecular intensities and differences.
5
0
CAngstromIl
Fig. 2. Experimental radial distribution function and difference curve.
tional amplitudes of closely spaced interatomic distances was constrained to the spectroscopic ratio (see Table I). The harmonic corrections Ar = r, - rz were incorporakd in the least squares analysis. With the above assumptions six geometric parameters and six vibrational amplitudes were refined simultaneously. Although some correlation coefficients between parameters are rather large (CF/CO = 4.82, CO/COCl = -6.61, CF/Z(CF) = 0.78, CO/Z(CF) = 4.86 and COCl/I(F.-F) = O-77), the six peaks in the radial distribution function allow an accurate and reliable determination of the geometric parameters. The results of the least squares analysis are summarized in Table 1. Values for bond lengths are converted from rz to rg. Attempts to refine the bond angles F&F, and F&F, separately (i.e. C, instead of Cfv symmetry for the CFs group) caused additional high correlations between
313 TABLE Results
1 of least squares analysis
(a) Geometric 0.1%
parameters:
error limits
Bond
rg (A)
C-F O-C O-Cl
1.325 1.365 1.679
(b) Vibrational
C-F O-C O-Cl F.-F 0 - - Ft O.-F, C..CI Cl--F, CI..F, (c) Agreement = 5.2
amplitudes:
(.-) (7, (3)
error limits
scale error of
‘a (“I
FCF COCl Tilta
109.2 112.9 3.9
(0.7) (0.5) (0.8)
are 30 values
1 (e.d.)
1.32 1.36 1.67 2.15 2.14 2.20 2.54 2.90 3.68
0.043 0.047 0.048 0.061
(4)b (4)b (5) (17)’
0.044 0.048 0.049 0.053
0.068
(17)C)
0.059
(A)
I (spectr.)
(/k)d
K(290
K) (zQd
0.0042 0.0033 0.0075 0.0044 0.0049 0.0031 0.0022 0.0003 0.0011
0.061 0.120 0.060
0.079 (12) 0.110 (6) 0.061(9)
factors
a possible
Angle
r (A)
(70)
RN
=Tilt of CF, spectroscopic
are 20 values and include
RZ,
= 9.0
group towards oxygen value, dCalculated from
lone pairs. “CRatio force field of ref. 8.
of
amplitudes
constrained
to
these two angles and the tilt angle and the refined values were equal within their standard deviations. The C-O and C-F bond lengths in CF30C1 agree within their experimental uncertainties with the corresponding values for CF30CF3 (see Table Z), whereas the oxygen bond angle in CF30C1 is about 6” smaller than in CF30CF3. The C-O bonds in both compounds are considerably shorter TABLE
2
‘=omparison
of geometric
Compound
C-O
CH,OCHSb CF,OCF ’ CH,OCld CF,OCle CF,OFf
1.410 1.369 1.389 1.365 1.395
parameters
for some
related
o-x (3) (4) (28) (7) (6)
1.674 (19) 1.679 (3) l-421(6)
compounds a Q
C-F
1.327
(2)
1.325 1.319
(3) (3)
=Oxygen bond angle. brs Values from ref. 9. ‘rg Values from ref. 11. erg Values from thk study. frs Values from ref. 3.
ref.
10.
drslr,
111.7 119.1 112.8 112.9 104.9
(4) (8) (21) (5) (6)
Values
from
314 th&in CHBOCHs. A comparison with &he structural pzameters of CHsOCl is not very helpful, since the experimental uncertainties for these parameters are rather large. The shortening of the. C-O bond in CH30CH3 upon CH3/CF3 substitution has .&en rationalized by polar effects [ 121 : the high positive net ch& of the CF9 carbon atom ,together with the negative net charge of oxygen results in an attractive polar effect and thus shortens the C-O bond in CFBOCF~ & compared to CHBOCHB. The carbon and oxygen net charges in CFBOCl will not be very qifferent from those in CFBOCFB, since the electronegativities of chlorine and the CF3 group are similar. Thus, we expect little difference in the C-O bond lengths of CFIOCFS and CFJOCl and this is confirmed by experiment_(Table 2). This rationalization implies positive net charges for chlorine, as well as for the CF3 groups. Fluorine is a stronger electron withdrawing substituent than chlorine or CF3 groups and we expect reduced electron. density at the oxygen atom in CFJOF. This, in turn, will reduce the bond strengthening due to polar effects and result in a longer C-O bond for CFBOF. The experimental value for this bond is ind&d Luger by about 0.03 A. The slightly shorter C-F bonds in CFBOF are also in agreement with this interpretation, since these bond lengths correlate with the effective electronegativity of the atom or group to which the CFJ group is bonded [12a, b] . Shortening of this bond in CF30F as compared to CF30Cl implies stronger electron withdrawing power of the OF group. Since we concluded from the variation of the C-O bond lengths a reduced electron density for the OF oxygen atom, the electron density of fluorine has to be considerably increased as compared to chlorine. An additional indication for a negatively charged fluorine atom is the small COF angle which can be rationalized as a result of electrostatic attraction between the positive.carbon, atom and fluorine. This angle is only slightly larger than the FOF angle in OF1 (103.2”) despite the much larger steric requirement of the CFJ group. This interpretation of our results is consistent with the available data and it supports the different chemical behaviour of these two compounds, resulting from a positive net charge on chlorine and a negative net charge on fluorine [13]. ACKNOWLEDGEMENTS
We acknowledge financial support by NATO National Science Foundation (CHE-8100156).
(RG. .384/83)
and the
REFERENCES 1 2 3 4
J. M. Shree-re, Adv. 1110%.Chem. Radiochem., 26 (1983) 119. K. K_ Johri and D. D. DesMarteau, J. Org. Chem., 48 (1983) 242. F. P. Diodati and L. S. Bartell, J. Mol. Struct., 8 (1971) 395. (a) G. E.- Gould, L. R. Anderson, D. E. Young and W. B. Fox, J. Am. Chem. Sot., 91 (1969) 1310. (b) C. J. Schack and W. Maya, J. Am. Chem. Sot., 91(1969) 2902.
315 er, Molecular 5 I-L oberhemm Structures by Diffraction Metho& Vol. 4, The Chemical Society, London, 1976, p. 24. 6 H. Oberhsnuner, W. Gambler and H. Willner, J. Mol. Struct., 70 (1981) 273. 7 J. Haase, Z. Naturforsch., TeiL A, 25 (1970) 936. 8 J. C. Kuo, D. D. DesMarteau, W. G. Fateley, R. M. Hammaker, C. J. Marsden and J. D. Witt, J. Raman Spectrosc., 9 (1980) 230. 9 U. Blukis, P. H. Kasai and R. J. Myers, J. Chem. Phys., 38 (1963) 2753. 10 A H. Lowrey, C. George, P. D’Antcnio and J. Karle, J. Mol. Struct, 63 (1980) 243. 11 J. S. Ridgen and S. S. Butcher, J. Chem. Phys, 40 (1964) 2109. 12 (a) V. Typke, M. Dakkouri and H. Oberhammer, J. Mol. Struck, 44 (1978) 85. (b) H. Oberhammer, J. MoL Struct., 28 (1975) 349. (c) H. Oberhammer, J. Fluorine Chem., 23 (1983) 147. 13 K. 0. Christe, J. Fluorine Chem, 22 (1983) 519.