Aug. 20, 1959
MOLECULAR
STRUCTURE O F
atoms for hydrogen atoms in this series due to a decrease in the ionic character of the chlorine atoms as more chlorine atoms are attached to the same carbon atom. Such a trend is observed for 1,ldichloroethane, methylchloroform and carbon tetrachloride, the values of the C-C1 distances being 1.795, 1.775 and 1.76 A., respectively, but an inconsistency occurs in ethyl chloride, where the C-Cl distance is 1.77 The C-C-C1 and Cl-C-C1 angles (110 f 4' and 109.5 1.5' respectively) obtained in this investigation are in excellent agreement with results obtained for most of the investigations on other chloroalkanes except t-butyl c h l ~ r i d e and 1,2-dichloropropane,8where the C-C-CI angles are approximately 107 and 1OSo, respectively.
A.
*
a-CHLOROCYCLOHEXANO"
4159
The greatest difference between the results of this investigation and those of other investigations, however, lies in the non-bonded C-C1 distance (2.745 f 0.03 A,), which is longer than any value reported previously, except for the early value reported by Beach and S t e v e n ~ o n 'for ~ ethyl chloride (2.74 f 0.02 The large uncertajnty on the C-C distance in 1,l-dichloroethane makes it impossible t o be certain that this distance is different from the corresponding distance in 1,2-dichloroethane, but it does seem most likely that the latter compound is very unusual in this respect. ~ (13) ~ ~ J.~ Y. Bench and D. 1'. Ste.r.ensoo, Tms J I , I I R X A I61, . , 2G43
A.).
(1939). T,AFAYETTE, TNDIASA
[CONTRIBUTION FROM TFIE CHEMICAL LABORATORY,
TOKYO INSTITUTE
O F TECHNOIXKY]
The Molecular Structure of a-Chlorocyclohexanone BY KUNIOKOZIMA AND YOSHIKO YAMANOUCIII RECEIVED MARCII 9, 1959 By the measurements of the infrared spectra and t h e dipole moment of a-chlorocyclohexanone the following results have been obtained t h a t the molecules of a-chli~rocyclohexanonein the vapor or the liquid state are in a dynamic equilibrium of mutually convertible isomers represented by the usual symbols as follows ( e ) e (a) and t h a t the (e)-form is more stable in the liquid state and only this form persists in the solid state. T h e energy difference between the isomers was approximately determined. Variation of the energy difference with solvents can be estimated by use of the reaction field theory of Onsager.
The measurements of infrared absorption spectra It has been well established t h a t the ring structure of various cyclohexane derivatives is the chair were made with a Perkin-Elmer 112 spectrometer. c NaCl and KBr prisms were employed to cover form. Because the valency angle of O=C( C 2 to 25 p . A CaFz prism was used to study the band shape of the C=O stretching vibrations. The Raman spectrograph and other apparatus of cyclohexanone should be about 120', its ring structure may be somewhat different from t h a t of used in this work have been described previously. la The wave number readings of the Raman bands usual cylcohexane derivatives. I t seems reasonable, however, that the ring structure is nearly and the infrared absorption maxima are listed the chair form. We can expect, therefore, that the in Table I. The intensities are shown by the usual molecules of a-chlorocyclohexanone in the vapor symbols, respectively. Carbon disulfide was used or the liquid state are in a dynamic equilibrium for obtaining the spectra in non-polar solvent. of the two mutually convertible isomers (inverted Because of the overlap of the absorption of carbon isomers)' represented by the usual symbols2 disulfide and that of the solute, the bands a t 1435 and 1450 cm.-' for non-polar solvents were obas tained in carbon tetrachlaride. ( e ) Z (a) I n order to determine the energy difference where e and a represent the position of chlorine atom attached to the ring, respectively. Both between the two isomers, the temperature dependence of the relative intensities of the two bands at forms are shown schematically in Fig. 1. In an earlier paper3 i t was described t h a t most 917 and 933 cm.-l which are due to the different of the molecules of a-chlorocyclohexanone in the forms of the compound was measured for the CS2 liquid exist as the axial form, although a small dilute solution and for the pure liquid. The true integrated absorption intensities A corrected for amount of the equatorial form probably exists. This work was undertaken with the primary finite slit widths were calculated from the equation A = K ( 1/CL) loge( T o / T ) v ( m a x ) X Avnl/2 purpose of determining the energy difference between the two isomers, special interest being where the letters have their usual meanings. The centered in the determination of the more stable values of K were obtained from the table of Ramform of this compound. say.5 The results obtained are shown in Table 11. a-Chlorocyclohexanone was prepared by the The dipole moment was measured by the usual method of Bartlett and Rosenwald4 and had b.p. solution method. The results are shown in Table 71.5-72.5' a t 6 mm., m.p. 23.0'. 111. ( 1 ) (a) K . Kozima a n d T. Yoshino, THIS J O U R N A L76, , 1GG (1953); ( b ) K . Kozima, K . Sakashita and S. h l a e d a , ibid., 76, 1SGS (1954). (2) D. H . R. Barton, 0. Hassel, K . S. Pitzer a n d V. Prelog, Knlzlre, 173, 1090 (1053); Science, 119, 49 (1953). (3) E. J , Corey, THISJ O U R N A L 76, , 2301 (1953). (4) P. D. Bartlett a n d R . H . Rosenwald, ibid., 66, 1992 (1834).
Discussion of Results As is clear i n Table I, the infrared bands of the liquid spectra are divided into two groups, ac( 3 ) D. A. R a m s a y , rbzd., 74, 72 (19.52).
\'ol. SI
41 00 TABLE I \.IBRATION
R a m a n spectra, cm. - 1 Liquid
421(2) 486( G )
538( 10br) c,03(4) G98(3) 716(4) 752(3) 790(3) 832( 5br)
855(4) 890(4) 919( 1)
SPECTRA O F a-CHLOROCYCLOHEX.4NONEn
Vapor
444(w) 471 476( w) 484 538(s) 542( 111) (;97(m) 705( S ) i12(m) it54(wbr) 798(m) 818(w) 825(1n) 833(n) #lo( rr.)
1121(4) 1192(4)
1250(6) 130S(G) 1332(2) 1425(2) 1447(8) 1721(5)
.... 891( w ) 9lO(W) 918(in) 925( IT)
974(m) 982(m) 991(w) 1020(w) 1065(111br ) ....
1110(I l l ) 11l7(s) 1125(rn) ll93(lll) .... 1227(sbr) 1203(m ) 1290(171) 1307inbr ) 1317(\v 1 13
