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Microwave spectra and structure of 1,3-dichlorobenzene
Journal of Molecular Structure, 295 (1993) 101-104 0022-2860/93/$06.00 0
1993 - Elsevier Science Publishers
101 B.V., Amsterdam
Microwave spectra and structure of 1,3-dichlorobenzene Masao Onda*, Masahiko Atsuki, Junko Yamaguchi, Kazuhiro Suga, Ichiro Yamaguchi Department
of Chemistry, Faculty of Science and Technology, Sophia University, Tokyo 102, Japan
(Received 13 October 1992)
Abstract The microwave spectra of 1,3-dichlorobenzenes (“Cl, and 35C1“Cl) and their six monodeuterated species have been observed and analyzed in the frequency range lo-40 GHz. The r,, structure of the molecule has been calculated by means of an elaborate least-squares procedure. The determined r,, bond lengths (in pm) and bond angles (in degrees) are as follows: rc_c = 138.9-139.5, rc_H = 108.3-l 10.8, rc<, = 172.7(35), LCCC = 118.9-121.0, LC1(7)C(l)C(2) = 119.2(36), L C(3)C(4)H(lO) = 118.4(44). The following distortions in the structure have been found: the distortion of the benzene ring is of the same extent as in chlorobenzene (CCC angles are 119.4-120.7’) and ortho-hydrogen H(lO) is located close to the chlorine atom.
Introduction A microwave spectroscopic study of 1,3-dichlorobenzene was previously published by us for the normal species ( 1,3-35C1,C,H, and 1,3-35C137C1C,H,) [l]. The rotational constants and quadrupole coupling constants of the chlorine nuclei were obtained and the planarity of the molecule was confirmed. The r, structure was also obtained from the rotational constants of six isotopic species [2]. Anderson et al. [3] determined the molecular structure of this molecule by the combined analysis of electron diffraction, rotational constant and liquid crystal nuclear magnetic resonance data. Merke et al. [4] observed the hyperfine structure of the molecule by Fourier transform microwave spectro* Corresponding
author.
scopy and analyzed the quadrupole coupling to the second order. In this study, we observed the spectra of two normal species and six monodeuterated species, and obtained the rs coordinates of hydrogen as well as the r, structure of the molecule. The ring distortion and the deformation of the C-Cl and C-H bonds which appear in the r0 structure are discussed.
Experimental The microwave spectrum was observed using a conventional spectrometer with 100 kHz square wave Stark modulation. A synthesizer (HP-8672A) for 8-18 GHz and a YIG-tuned GaAs oscillator (Watkins-Johnson 5610-302FD) for 26540 GHz
102 were used as the microwave sources. The waveguide was cooled with dry ice and the sample pressure in it was below 6 Pa. Samples of the d4 and d5 species were synthesized from 4- and 5-bromo1,3-dichlorobenzene with D,O by a Grignard reaction. As the d2 species could not be obtained by the Grignard reaction, even when using an Li compound, we synthesized it by thermal decarboxylation of 2,6-dichlorobenzoic acid-OD, which was prepared by mixing its normal species with D,O for 6 h at 50-60°C. The obtained substance was dried in vacua. The deuterium exchange was estimated to be about 90% by the mass spectrum. The obtained OD-species was passed through a heated quartz tube (25cm in length and 1 cm in diameter) and introduced into an X band waveguide (1.5 m length). The spectrum of 1,3-dichlorobenzene-d, was observed at a temperature above that of the quartz tube (55OOC); the intensity of the spectral lines of the vibrational ground state was at a maximum at 750°C. We observed the lines of the d2 species and the normal species, which were present in small amounts.
Results and discussion Intense lines of the b-type R- and Q-branch transitions appeared near the predicted frequencies from the rotational constants of the two normal species, 35C1, and 3sC137C1[l]. The quadrupolar coupling of the chlorine nuclei with the molecular rotation gives characteristic hyperfine splitting to each of the rotational transitions. The hyperfine splitting was predicted from the quadrupole coupling constants obtained in the previous work [l]. Many rotational transitions were observed as triplets. The center peak position of the triplet was taken as the unperturbed frequency. This was also adopted in cases where the two chlorine atoms were non-equivalent in the molecule. This was justified because only rather high J transitions were observed.” The rotational constants obtained are shown in Table 1.
M. Onda et al/J. Mol. Struck, 295 (1993) 101-104
r, coordinate The observed inertia defect had a small positive value, as expected for a planar ring molecule with small amplitude out-of-plane vibrations of substituents. The rs coordinates of the Cl and H atoms were obtained using Kraitchman’s equation for a planar molecule, as given in Table 2. The nonbonded distances, H ... H and H ... Cl, were calculated using the rs coordinates. The rs non-bonded distances are nearly equal to those of electron diffraction data except for two distances, Cl(9) a**H( 10) and H(8) ... H( 10). The non-bonded distances of Cl ... orthohydrogen in 1,3-dichlorobenzene, Cl(7) ... H(8) (284.9 pm) and Cl(9) ***H( 10) (283.0 pm) are nearly equal to that in monochlorobenzene (284.48pm) [5]. However, the non-bonded distance in 1,2-dichlorobenzene (280.9 pm) [2] is much shorter than in the above two molecules. The non-bonded distances between Cl and meta- or para-hydrogen are almost the same in these three molecules. The distance between the two hydrogen atoms located para to each other, H(8) ... H(l l), in 1,3-dichlorobenzene (498.6pm), is slightly greater than the corresponding non-bonded distance in benzene, 495.4 pm [6]. To obtain a complete rs structure of the substituted benzene, we have to observe isotopic species with 13Cin the benzene ring. Synthesis of the 13C species is very tedious and expensive, and only a few complete r, structures of monosubstituted benzene have been reported so far (C6H,X, X=F, Cl, CN, OH, NH,, CH,) [7]. There are no data for the rs structure of disubstituted benzene. This time, we obtained the rOstructure of 1,3-dichlorobenzene using the same method as in the case of 1,2-dichlorobenzene [8].
“A list of the observed transition frequencies is available from B.L.L.D. as Supplementary Publication number SUP 26467 (2 pages).
M. Onda et al/J.
Table 1 Rotational
Mol. Struct., 295 (1993)
constants
103
101-104
(MHzpb and inertia defect (uA2) of 1,3-dichlorobenzene
Species”
A
B
c
I,-I,-&
[35,35]d [35,37]d [35,35,2d] [35,35,4dl [35,35,5dl [35,37,2dl [37,35,4dl [35,37,5dl
2832.335(22) 2811.643(55) 2783.445(26) 2773.938( 12) 2678.515(18) 2767.56(12) 2754.787(20) 2659.010(26)
862.829(S) 842.254(10) 862.279( 12) 855.909(4) 862.834(5) 841.73(l) 835.315(5) 842.242(6)
661.270(4) 648.017(9) 658.679( 11) 654.002(3) 652.520(3) 645.46( 1) 640.880(5) 639.555(6)
0.100(9) 0.109(21) 0.074( 10) 0.101(7) 0.105(8) - 0.038 0.099( 11) 0.101(14)
“The centrifugal distortion constants (kHz) are assumed to be the same as for [35,35] in ref. 1: z,,,,, = 0.3(9), rbbbb= - 0.18(l), 0.09(6) and rabub= 0 (assumed). Z,,bb = bFigures in parentheses are the uncertainties in the last digits of the value, calculated from 2.5 times the standard deviation. ’ [35,37,4dj represents the species 1,3-dichlorobenzene-1-SSCl-3-37C1-4-d, etc. dRef. 1.
r, structure Assuming a rigid planar structure for this molecule, only two moments of inertia are independent for each of the eight species. Using the
Table 2 r, Coordinates of chlorine and hydrogen, distances of 1,3-dichlorobenzene (in pm)
Cl H(8) H(l0) H(l1)
lal
IQ
ICI
269.06(7) Ob 216.69(8) Ob
83.06(23) 176.88(9) 195.00(9) 320.20(6)
Ob Ob Ob Ob
Non-bonded
Cl(7) ‘. Cl(9) Cl(7). . . H(8) Cl(9). . H(lO) Cl(7). . . H( 10) Cl(9) . . . H( 11) H(8). . . H( 10) H(8). . . H( 11) H(lO)...H(ll) H(lO)...H(12)
and non-bonded
distance
ED + MW’
r,
538.1(l) 285.2(2) 285.4(2) 560.8(3) 485.9(3) 432.5(5) 498.6(6) 250.0(3) 433.6(6)
538.1(l) 284.9 283.0(3) 559.7 484.8(l) 430.4 497.1 250.3(2) 433.4
a Uncertainties are calculated from the error in the observed rotational constant. bAssumed. ‘Ref. 3.
moments of inertia of the eight species in Table 1, eleven structural parameters have been derived as in Table 3 by the non-linear least-squares fitting on the SALS [9] system. The set consisting of 24 moments of inertia of all the isotopic species studied was used as the SALS input data. The signifi-
Table 3 Structural degrees)
parameters
of 1,3-dichlorobenzene
(in pm and
Parameter
Value
ED + MW”
ro C(2)-H(8) r, C(4)-H(lO) r, C(5)-H(11) r, C(3)-Cl(9)
110.8(42) 109.1(38) 108.3(57) 172.7(35) 139.5(47) 139.4(51) 138.9b
110.71(64) 109.73(23) 1lOSO(66) 173.90(14) 139.06(38) 139.44(32) 140.69(29)
118.9(44) 120.9(41) 119.0(29) 118.4(44) 120.1s 119.2(36) 122.4b 121.0b 120.5b 119.5b
118.09(38) 122.27(18) 118.91(27) 121.19(22) 118.83(22) 118.13(23) 120.68(25) 121.10(40) 120.96b 119.45b
r. C(2)-C(3) r. C(3)-C(4) r0 C(4)-C(5) ~C(l)C(2)c(3) L C(2)C(3)C(4) LC(2)C(3)C1(9) LC(3)C(4)H(lO) L C(4)C(3)C1(9) L C(3)C(4)C(5) L C(5)C(4)H( 10) L C(4)C(5)C(6) LC(l)C(2)H(8) L C(4)C(5)H( 11) “Ref. 3. b Derived parameter.
104
cance attached to the input data was calculated from the standard deviation of the observed rotational constants, and was used as the fitting criterion for the normalized residual. The structural parameters obtained are shown in Table 3. In this non-linear fitting procedure, the result depended sensitively on the assumed initial values and did not always converge. To obtain a converged result, loose restriction on the initial values must be imposed. The values of the restriction are 0.005.pm and lo for bond lengths and bond angles, respectively. These did not rigidly limit the fitted values but influenced the significance of the final values. Several magnitudes of the restriction range were tried. In every case each of the converged values was the same within the corresponding significance. The standard deviations of the fitting were 0.05 u A2. The distortion of the ring in monochlorobenzene has been reported by Michel et al. [5]. Results for 1,3-dichlorobenzene inferred from the obtained r0 structural parameters indicate that the distortion of the benzene ring is rather small: bond length rc_c = 138.9-139.5pm (average 139.7pm) and bond angle LCCC = 118.9-121.0”. The characteristic features of this molecule are a small “pushin effect” at the ipso-carbon atom and alternation of the magnitude of the LCCC angle as the position goes from ipso to para. The magnitude of the “push-in”, estimated by distortion of the C-C(ipso)-C angle, is equal to that in monochlorobenzene. However, this kind of distortion is very small compared with that in fluorobenzene, as reported by Doraiswamy and Sharma [lo], where the angle LC(6)C(l)C(2) is 123.4’. They suggested from electronegativity considerations that the ring distortion due to a chlorine substituent would be rather small. Certain distortion in the bond angles is apparent: LC(2)C(3)C1(9) = 119.0’ and LC(3)C(4)H(lO) = 118.4”. The two chlorine atoms are close to H(8) and the two C-H bonds
M. Onda etal./J. Mol. Strut.,295 (1993) 101-104
adjacent to the C-Cl bond bend toward the Cl atom side. A similar tendency appears in the rs structure. This is just as if the hydrogen and chlorine atoms attract each other. The deflection angle of the C-Cl bond from the bisector of the ipso-carbon is about 1”. Only a small distortion appeared on the opposite side of the ring to the Cl atoms, so it is concluded that the molecular structure relaxation results mainly from the rearrangement of bonding electrons in the substituent moiety. In the present case the significant distortion is the deflection of the C-Cl bond by about 1” in the molecular plane owing to the attraction between the chlorine atom and ortho-hydrogen. References M. Onda, 0. Ohashi and I. Yamaguchi, J. Mol. Struct., 31 (1976) 203. M. Onda, Nippon Kagaku Kaishi, (1986) 1476. D.G. Anderson, S. Cradock, P.B. Liescheski and D.W.H. Rankin, J. Mol. Struct., 216 (1990) 181. I. Merke, Ch. Keussen, H. Dreizler and M. Onda, Z. Naturforsch., Teil A, 45 (1990) 1273. F. Michel, H. Nery, P. Nosberger and G. Roussy, J. Mol. Struct., 30 (1976) 409. M. Oldani and A. Bauder, Chem. Phys. Lett., 108 (1984) 7. (X=F) L. Nygaard, I. Bojesen, T. Pedersen and J.R. Andersen, J. Mol. Struct., 2 (1968) 209; (Cl) F. Michel, H. Nery, P. Nosberger and G. Roussy, J. Mol. Struct., 30 (1976) 409; (CN) J. Casado, L. Nygaard and G.O. Sorensen, J. Mol. Struct., 8 (1971) 211; (OH) N.W. Larsen, J. Mol. Struct., 51 (1979) 175; (NH,) D.G. Lister, J.K. Tyler, J.H. Hog and N.W. Larsen, J. Mol. Struct., 23 (1974) 253; (CH,) V.A. Ebrahimi, A. Choplin, J. Demaison and G. Roussy, J. Mol. Spectrosc., 89 (1981) 42; W.A. Kreiner, H.D. Rudolph and B.T. Tan, J. Mol. Spectrosc., 48 (1973) 86. 8 M. Onda, M. Ueda, M. Atsuki, J. Yamaguchi and I. Yamaguchi, J. Mol. Struct., 147 (1986) 77. 9 T. Nakagawa and Y. Oyanagi, Program system SALS, computer centre of the University of Tokyo, 1980. 10 S. Doraiswamy and S.D. Sharma, J. Mol. Struct., 102 (1983) 81.
1993 - Elsevier Science Publishers
101 B.V., Amsterdam
Microwave spectra and structure of 1,3-dichlorobenzene Masao Onda*, Masahiko Atsuki, Junko Yamaguchi, Kazuhiro Suga, Ichiro Yamaguchi Department
of Chemistry, Faculty of Science and Technology, Sophia University, Tokyo 102, Japan
(Received 13 October 1992)
Abstract The microwave spectra of 1,3-dichlorobenzenes (“Cl, and 35C1“Cl) and their six monodeuterated species have been observed and analyzed in the frequency range lo-40 GHz. The r,, structure of the molecule has been calculated by means of an elaborate least-squares procedure. The determined r,, bond lengths (in pm) and bond angles (in degrees) are as follows: rc_c = 138.9-139.5, rc_H = 108.3-l 10.8, rc<, = 172.7(35), LCCC = 118.9-121.0, LC1(7)C(l)C(2) = 119.2(36), L C(3)C(4)H(lO) = 118.4(44). The following distortions in the structure have been found: the distortion of the benzene ring is of the same extent as in chlorobenzene (CCC angles are 119.4-120.7’) and ortho-hydrogen H(lO) is located close to the chlorine atom.
Introduction A microwave spectroscopic study of 1,3-dichlorobenzene was previously published by us for the normal species ( 1,3-35C1,C,H, and 1,3-35C137C1C,H,) [l]. The rotational constants and quadrupole coupling constants of the chlorine nuclei were obtained and the planarity of the molecule was confirmed. The r, structure was also obtained from the rotational constants of six isotopic species [2]. Anderson et al. [3] determined the molecular structure of this molecule by the combined analysis of electron diffraction, rotational constant and liquid crystal nuclear magnetic resonance data. Merke et al. [4] observed the hyperfine structure of the molecule by Fourier transform microwave spectro* Corresponding
author.
scopy and analyzed the quadrupole coupling to the second order. In this study, we observed the spectra of two normal species and six monodeuterated species, and obtained the rs coordinates of hydrogen as well as the r, structure of the molecule. The ring distortion and the deformation of the C-Cl and C-H bonds which appear in the r0 structure are discussed.
Experimental The microwave spectrum was observed using a conventional spectrometer with 100 kHz square wave Stark modulation. A synthesizer (HP-8672A) for 8-18 GHz and a YIG-tuned GaAs oscillator (Watkins-Johnson 5610-302FD) for 26540 GHz
102 were used as the microwave sources. The waveguide was cooled with dry ice and the sample pressure in it was below 6 Pa. Samples of the d4 and d5 species were synthesized from 4- and 5-bromo1,3-dichlorobenzene with D,O by a Grignard reaction. As the d2 species could not be obtained by the Grignard reaction, even when using an Li compound, we synthesized it by thermal decarboxylation of 2,6-dichlorobenzoic acid-OD, which was prepared by mixing its normal species with D,O for 6 h at 50-60°C. The obtained substance was dried in vacua. The deuterium exchange was estimated to be about 90% by the mass spectrum. The obtained OD-species was passed through a heated quartz tube (25cm in length and 1 cm in diameter) and introduced into an X band waveguide (1.5 m length). The spectrum of 1,3-dichlorobenzene-d, was observed at a temperature above that of the quartz tube (55OOC); the intensity of the spectral lines of the vibrational ground state was at a maximum at 750°C. We observed the lines of the d2 species and the normal species, which were present in small amounts.
Results and discussion Intense lines of the b-type R- and Q-branch transitions appeared near the predicted frequencies from the rotational constants of the two normal species, 35C1, and 3sC137C1[l]. The quadrupolar coupling of the chlorine nuclei with the molecular rotation gives characteristic hyperfine splitting to each of the rotational transitions. The hyperfine splitting was predicted from the quadrupole coupling constants obtained in the previous work [l]. Many rotational transitions were observed as triplets. The center peak position of the triplet was taken as the unperturbed frequency. This was also adopted in cases where the two chlorine atoms were non-equivalent in the molecule. This was justified because only rather high J transitions were observed.” The rotational constants obtained are shown in Table 1.
M. Onda et al/J. Mol. Struck, 295 (1993) 101-104
r, coordinate The observed inertia defect had a small positive value, as expected for a planar ring molecule with small amplitude out-of-plane vibrations of substituents. The rs coordinates of the Cl and H atoms were obtained using Kraitchman’s equation for a planar molecule, as given in Table 2. The nonbonded distances, H ... H and H ... Cl, were calculated using the rs coordinates. The rs non-bonded distances are nearly equal to those of electron diffraction data except for two distances, Cl(9) a**H( 10) and H(8) ... H( 10). The non-bonded distances of Cl ... orthohydrogen in 1,3-dichlorobenzene, Cl(7) ... H(8) (284.9 pm) and Cl(9) ***H( 10) (283.0 pm) are nearly equal to that in monochlorobenzene (284.48pm) [5]. However, the non-bonded distance in 1,2-dichlorobenzene (280.9 pm) [2] is much shorter than in the above two molecules. The non-bonded distances between Cl and meta- or para-hydrogen are almost the same in these three molecules. The distance between the two hydrogen atoms located para to each other, H(8) ... H(l l), in 1,3-dichlorobenzene (498.6pm), is slightly greater than the corresponding non-bonded distance in benzene, 495.4 pm [6]. To obtain a complete rs structure of the substituted benzene, we have to observe isotopic species with 13Cin the benzene ring. Synthesis of the 13C species is very tedious and expensive, and only a few complete r, structures of monosubstituted benzene have been reported so far (C6H,X, X=F, Cl, CN, OH, NH,, CH,) [7]. There are no data for the rs structure of disubstituted benzene. This time, we obtained the rOstructure of 1,3-dichlorobenzene using the same method as in the case of 1,2-dichlorobenzene [8].
“A list of the observed transition frequencies is available from B.L.L.D. as Supplementary Publication number SUP 26467 (2 pages).
M. Onda et al/J.
Table 1 Rotational
Mol. Struct., 295 (1993)
constants
103
101-104
(MHzpb and inertia defect (uA2) of 1,3-dichlorobenzene
Species”
A
B
c
I,-I,-&
[35,35]d [35,37]d [35,35,2d] [35,35,4dl [35,35,5dl [35,37,2dl [37,35,4dl [35,37,5dl
2832.335(22) 2811.643(55) 2783.445(26) 2773.938( 12) 2678.515(18) 2767.56(12) 2754.787(20) 2659.010(26)
862.829(S) 842.254(10) 862.279( 12) 855.909(4) 862.834(5) 841.73(l) 835.315(5) 842.242(6)
661.270(4) 648.017(9) 658.679( 11) 654.002(3) 652.520(3) 645.46( 1) 640.880(5) 639.555(6)
0.100(9) 0.109(21) 0.074( 10) 0.101(7) 0.105(8) - 0.038 0.099( 11) 0.101(14)
“The centrifugal distortion constants (kHz) are assumed to be the same as for [35,35] in ref. 1: z,,,,, = 0.3(9), rbbbb= - 0.18(l), 0.09(6) and rabub= 0 (assumed). Z,,bb = bFigures in parentheses are the uncertainties in the last digits of the value, calculated from 2.5 times the standard deviation. ’ [35,37,4dj represents the species 1,3-dichlorobenzene-1-SSCl-3-37C1-4-d, etc. dRef. 1.
r, structure Assuming a rigid planar structure for this molecule, only two moments of inertia are independent for each of the eight species. Using the
Table 2 r, Coordinates of chlorine and hydrogen, distances of 1,3-dichlorobenzene (in pm)
Cl H(8) H(l0) H(l1)
lal
IQ
ICI
269.06(7) Ob 216.69(8) Ob
83.06(23) 176.88(9) 195.00(9) 320.20(6)
Ob Ob Ob Ob
Non-bonded
Cl(7) ‘. Cl(9) Cl(7). . . H(8) Cl(9). . H(lO) Cl(7). . . H( 10) Cl(9) . . . H( 11) H(8). . . H( 10) H(8). . . H( 11) H(lO)...H(ll) H(lO)...H(12)
and non-bonded
distance
ED + MW’
r,
538.1(l) 285.2(2) 285.4(2) 560.8(3) 485.9(3) 432.5(5) 498.6(6) 250.0(3) 433.6(6)
538.1(l) 284.9 283.0(3) 559.7 484.8(l) 430.4 497.1 250.3(2) 433.4
a Uncertainties are calculated from the error in the observed rotational constant. bAssumed. ‘Ref. 3.
moments of inertia of the eight species in Table 1, eleven structural parameters have been derived as in Table 3 by the non-linear least-squares fitting on the SALS [9] system. The set consisting of 24 moments of inertia of all the isotopic species studied was used as the SALS input data. The signifi-
Table 3 Structural degrees)
parameters
of 1,3-dichlorobenzene
(in pm and
Parameter
Value
ED + MW”
ro C(2)-H(8) r, C(4)-H(lO) r, C(5)-H(11) r, C(3)-Cl(9)
110.8(42) 109.1(38) 108.3(57) 172.7(35) 139.5(47) 139.4(51) 138.9b
110.71(64) 109.73(23) 1lOSO(66) 173.90(14) 139.06(38) 139.44(32) 140.69(29)
118.9(44) 120.9(41) 119.0(29) 118.4(44) 120.1s 119.2(36) 122.4b 121.0b 120.5b 119.5b
118.09(38) 122.27(18) 118.91(27) 121.19(22) 118.83(22) 118.13(23) 120.68(25) 121.10(40) 120.96b 119.45b
r. C(2)-C(3) r. C(3)-C(4) r0 C(4)-C(5) ~C(l)C(2)c(3) L C(2)C(3)C(4) LC(2)C(3)C1(9) LC(3)C(4)H(lO) L C(4)C(3)C1(9) L C(3)C(4)C(5) L C(5)C(4)H( 10) L C(4)C(5)C(6) LC(l)C(2)H(8) L C(4)C(5)H( 11) “Ref. 3. b Derived parameter.
104
cance attached to the input data was calculated from the standard deviation of the observed rotational constants, and was used as the fitting criterion for the normalized residual. The structural parameters obtained are shown in Table 3. In this non-linear fitting procedure, the result depended sensitively on the assumed initial values and did not always converge. To obtain a converged result, loose restriction on the initial values must be imposed. The values of the restriction are 0.005.pm and lo for bond lengths and bond angles, respectively. These did not rigidly limit the fitted values but influenced the significance of the final values. Several magnitudes of the restriction range were tried. In every case each of the converged values was the same within the corresponding significance. The standard deviations of the fitting were 0.05 u A2. The distortion of the ring in monochlorobenzene has been reported by Michel et al. [5]. Results for 1,3-dichlorobenzene inferred from the obtained r0 structural parameters indicate that the distortion of the benzene ring is rather small: bond length rc_c = 138.9-139.5pm (average 139.7pm) and bond angle LCCC = 118.9-121.0”. The characteristic features of this molecule are a small “pushin effect” at the ipso-carbon atom and alternation of the magnitude of the LCCC angle as the position goes from ipso to para. The magnitude of the “push-in”, estimated by distortion of the C-C(ipso)-C angle, is equal to that in monochlorobenzene. However, this kind of distortion is very small compared with that in fluorobenzene, as reported by Doraiswamy and Sharma [lo], where the angle LC(6)C(l)C(2) is 123.4’. They suggested from electronegativity considerations that the ring distortion due to a chlorine substituent would be rather small. Certain distortion in the bond angles is apparent: LC(2)C(3)C1(9) = 119.0’ and LC(3)C(4)H(lO) = 118.4”. The two chlorine atoms are close to H(8) and the two C-H bonds
M. Onda etal./J. Mol. Strut.,295 (1993) 101-104
adjacent to the C-Cl bond bend toward the Cl atom side. A similar tendency appears in the rs structure. This is just as if the hydrogen and chlorine atoms attract each other. The deflection angle of the C-Cl bond from the bisector of the ipso-carbon is about 1”. Only a small distortion appeared on the opposite side of the ring to the Cl atoms, so it is concluded that the molecular structure relaxation results mainly from the rearrangement of bonding electrons in the substituent moiety. In the present case the significant distortion is the deflection of the C-Cl bond by about 1” in the molecular plane owing to the attraction between the chlorine atom and ortho-hydrogen. References M. Onda, 0. Ohashi and I. Yamaguchi, J. Mol. Struct., 31 (1976) 203. M. Onda, Nippon Kagaku Kaishi, (1986) 1476. D.G. Anderson, S. Cradock, P.B. Liescheski and D.W.H. Rankin, J. Mol. Struct., 216 (1990) 181. I. Merke, Ch. Keussen, H. Dreizler and M. Onda, Z. Naturforsch., Teil A, 45 (1990) 1273. F. Michel, H. Nery, P. Nosberger and G. Roussy, J. Mol. Struct., 30 (1976) 409. M. Oldani and A. Bauder, Chem. Phys. Lett., 108 (1984) 7. (X=F) L. Nygaard, I. Bojesen, T. Pedersen and J.R. Andersen, J. Mol. Struct., 2 (1968) 209; (Cl) F. Michel, H. Nery, P. Nosberger and G. Roussy, J. Mol. Struct., 30 (1976) 409; (CN) J. Casado, L. Nygaard and G.O. Sorensen, J. Mol. Struct., 8 (1971) 211; (OH) N.W. Larsen, J. Mol. Struct., 51 (1979) 175; (NH,) D.G. Lister, J.K. Tyler, J.H. Hog and N.W. Larsen, J. Mol. Struct., 23 (1974) 253; (CH,) V.A. Ebrahimi, A. Choplin, J. Demaison and G. Roussy, J. Mol. Spectrosc., 89 (1981) 42; W.A. Kreiner, H.D. Rudolph and B.T. Tan, J. Mol. Spectrosc., 48 (1973) 86. 8 M. Onda, M. Ueda, M. Atsuki, J. Yamaguchi and I. Yamaguchi, J. Mol. Struct., 147 (1986) 77. 9 T. Nakagawa and Y. Oyanagi, Program system SALS, computer centre of the University of Tokyo, 1980. 10 S. Doraiswamy and S.D. Sharma, J. Mol. Struct., 102 (1983) 81.