KURTMISLOWAND CHARLES L. HAMERMESH
1590
It is obvious that aromatic substitution suffers steric hindrance, for as the size of the substituent increases, the amount of ortho substitution decreases. In addition, the so-called law of invariable ortho-para substitution is not adhered to. When ortho substitution (in the cumene run) is substantially prevented, meta and para substitution are statistical in quantity. Acknowledgment.-We would like to express our
[CONTRIBUTION FROM THE
Vol. 77
deepest appreciation to Irving Goodman and Paul Wise of the Lewis Flight Propulsion Laboratory of the National Advisory Committee for Aeronautics in Cleveland, Ohio, for supplying us with pure saniples of o-methyl-, m-methyl-, a-ethyl-, m-ethyl- and o-isopropylbiphenyl. We also wish to thank Ernest Yeager for his advice in the performance of the infrared work described. CLEVELAND 6, OHIO
WM. H. NICHOLS CHEMICAL LABORATORY, SEW
YORK UNIVERSITY]
The Effect of Ring Formation on Optical Rotatory Power. A Comparison of the Optical Rotations of 2-Phenylcyclopentanone and of Some Acyclic a-Phenyl Ketones BY KURTMISLOWAND CHARLES L. HAMERMESH RECEIVED AUGUST30, 1954 2-Phenylcyclopentanone has been resolved via its tartrarnazone. The extraordinarily high value of the specific rotation of this ketone, [ ( Y ] ~ +4190° D (cyclohexane), is five t o ten times larger than that of any of ten acyclic analogs, whose maximum rotations have been established in this work. A convincing demonstration has thus been provided that ring formation results in an enhancement of optical activity.
While the problem of optical rotatory power may The present investigation was initiated with a be regarded, in principle, as solvedl1V2very few view toward subjecting this generalization to a simple empirical generalizations are known which somewhat more systematic experimental scrutiny. make possible predictions of rotatory power from The choice of the system to be studied, the a-phenyl an a priori inspection of over-all structural features. ketones, was motivated by the convenience entailed One of the most consistently successful such rules in determining the maximum rotations of the acyclic had already been noted by van't H ~ f f who , ~ re- members of the series (vide infra),while the selection marked that "the interaction of the several groups, of a five-membered ring for the cyclic ketone was rl, r2, r3 and r4 attached to the asymmetric carbon principally governed by the consideration that an atom which may be accompanied by ring formation, observed effect might be more pronounced in the appears to have quite an extraordinary influence on cyclopentane than in the cyclohexane system : the the magnitude of the sign of the rotation." This rotation of 3-methylcyclopentan~ne~ considerably effect on rotatory power of ring formation has been exceeds that of 3-methylcyclohexanone.9 Ten unbranched acyclic a-phenyl ketones (I), noted in miscellaneous instances, such as in comparisons of hydroxy acids with their lactone^,^ of containing a total of four to seven atoms in the diesters with cyclic ketoesters derived t h e r e f r ~ r n , ~straight-chain portion of the molecule, were studof acyclic with cyclic amino acids,6of alkylsuccinic ied for purposes of comparison of optical rotatory and alkylglutaric acids with their anhydride^,^ power with 2-phenylcyclopentanone. These keof polyols with (cyclic) aldohexoses and aldopen- tones, prepared by the reaction of partially resolved toses2 and of 3-methylpentanal with 3-methylcyclo- acids I1 and alkyllithium 111 frequently were conpentanone.2 Unfortunately, in none of the cited taminated with tertiary carbinols, formed by furcases are comparisons entirely satisfactory : either ther reaction of I and 1 1 1 . 1 0 Purification of the new asymmetric atoms are introduced, or the func- ketones involving negligible racemization could be tional groups are considerably different in the com- effected through hydrolysis of the recrystallized pared systems. Nevertheless the trend is unescap- semicarbazones in a refluxing ligroin-dilute hydroable, and it is a generally accepted dictum, based chloric acid mixture. The physical and optical on firm theoretical grounds, that ring formation properties of the ten ketones thus prepared arc enhances the rotatory power approximately ten- listed in Table I. fold.2 (1) E . g . , J. C. Kirkwood, J . Chem. P h y s . , 6 , 479 (1937); E. U. Condon, Reo. Modern P h y s . . 9,432 (1937); E.Huckel, Z.Elcklrochcm., 60, 13 (1944); W. Kuhn, i b i d . , 56, 506 (1952); G. W. van Vloten, Chem. Weckblad, 48, 977 (1952); T. R. Thornson, THISJOURNAL, 76, 6070 (1953). ( 2 ) W. J . Kauzman, J E. M'alter and 11. Eyring, Chcin. Revs., 2 6 , 3:39 (1940); cf. especially p . 376 R. (3) J . H . van't Hoff, "The Arrangement of Atoms in Space," 2nd cd. (translated hy A . Eiloart), Longmans, Green and Co , London,
1808, p. 146.
(4) I. I. Kutyukov, Bull. Siberiaa I n s t . Tech., 60, no. 2 (1929); C . A , , 24,2978 (1030); D. M Bovey and E. E. Turner, J. Chcm. Sac., 9223 (19.51); J. A. Reid and 13. I?, 'Tiirner, i b X , 3219 (1951). (i) A I{t%llrra ~ h d l . l>esroiitaiiirs, inpi, pi, r F i i L , 140, 1205 (1905). (181 I I? ILir*er, K i c . l r a v . c h i n , , 69, 4 1 0 (I!I50) ,;I
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