4628
L. A. STRAIT, K . KETCHAM, D.
spatial arrangement of the atoms and bonds t h a t have to be rearranged in the key step of the fragmentation of I1 and I X , respectively. In the ajmaline series, the hydrogen a t C-2 is sufficiently close to C-17 to lead to its migration with simultaneous aromatization of the dihydroindole to an indole system (I + Ib, see above) In the 2-epi series, this hydrogen is, however, trans and far away from C-17, thus blocking that process. Aromatization is only possible by rearranging the C-2, C-3 bond to a C - 3 , C - l i as implied in the process I X -+ IXa. I t should be noted, however, that the bonds broken and the bonds rearranged are spatially the same (around C-2) in both processes which thus are very closely related although leading to entirely different fragments. These two groups of epimers thus represent a rather unique example in which the stereochemistry a t one center so completely changes the fragmentation of a carbon skeleton. The effect is here so drastic because of the very rigid arrangement of the polycyclic ring system
JAMBOTKAR, A N D
V. P.SHAH
Vol. Ni
Experimental Mass Spectra.--The
conventional spectra were taken \\.?til ;L single-focusing mass spectrometer ( C E C 21-103C) equipped g with a lieated inlet system operated a t 175'; i o n i z i ~ ~currcnt 10 or 50 pa., ionizing voltage 70 v , T h e high-resolution spectra were obtained with a d ~ u b l e focusing inass spectrometer C E C 21-110~),using a pliotographic plate for recording. T h e snniples \yere introduced directly illtc, t h e ion source and perfluorokeroselie was used a s the ir1;iss standard; ionizing current 100 ~ a . , ionizing voltage TO v , All t h e line positions \vert. measured and then converted to accurate masses and corresponding elemental compositions wit11 the aid of a computer.'^ A selected grilup of these values is sho\vn in Fig. 1-6.
Acknowledgment.--1i.e are indebted to Drs. L\., I , Taylor and K . Seuss for gifts of sam,iles. This investigation was supported by research grants from the Satiorial Institutes of Health, Public Health Service 2 ) , arid the National Science Foundation (G-21087). 1\13) 11 1)esiderio a n d K . B i e m a n n . 1 2 t h Annual Conference o n I 1 a b . i Specti-ornetel-s,l l u n t l eal. J u n e . 1064
THE DEPARTMENT OF PHARMACEUTICAL CHEMISTRY A N D T H E SPECTROGRAPHIC LABORATORY, UA'IVERSITY O F CALIFORNIA MEDICAL C E N T E R , S A S FRASCISCO 22, CALIFORSIA]
[COSTRIBUTION FROM
Three-Membered Rings. I. Conjugative Properties and Electronic Spectra of Arylcyclopropanes, Oxiranes, and Thiiranes' BY L. A . STRAIT, ROGERKETCHALI, D.
JAAIBOTKAK, ASII
I-INOU P.SHAH
RECEIVED M A Y11, 1981 T h e ultraviolet spectra of a series of p-substituted plienylcyclopropaiies, styrene oxides, and styrene sulfides have been examined with regard t o chromophoric enhancement a s measured by the effect of the p-substitution on the "primary" ( ~ . l l g - ~ B , uelectronically ) forbidden transition in benzene I t is shown t h a t , relative t o benzene, oxirane a n d thiirdne are electron withdrawing, whereas cyclopropane is electron donating. T h u s pmethosy substitution was observed t o shift conjugatively and enhance the ultraviolet "primary" absorption bands of phenyloxirane a n d thiirane b u t had little effect on phenylcyclopropane; p-nitro substitution showed the reverse effect. These observations are in agreement with second-order resonance effects and clarify some of the conflicting observations and conclusions concerning the unsatutatiori properties of t h e three-membered ring systems.
The electronic spectra of molecules containing threemembered rings adjacent to unsaturated groups have provided an effective method of demonstrating the conjugative properties arising from the unsaturation character of these rings.* These effects in cyclopropane have been documented by a variety of physical3 and chemical4 techniques and have been described theoretically by Coulsonj and Matsen6 and their coworkers ( I ! S u p p o r t e d . in p a r t , b y C a n c e r Research F u n d s , University of California. a n d a n American Cancer Society Institutional G r a n t I N 331). T h i s work h a s been reported in p a r t a t t h e 1963 P i t t s b u r g h C o n f e r e n c e on Analytical C h e m i s t r y a n d Applied Spectroscopy a n d a t t h e 147th S a t i o n a l M e e t i n g of t h e h m e r i c a n Chemical Society, Philadelphia, P a . , April, 1984. Abstractpd from t h e Ph.11. T h e s e s of I ) . J a m b o t k a r a n d V . P . S h a h ( 2 : ( a ) I< A . K a p h a e l , " C h e m i s t r y of C a r b o n C o m p o u n d s . ' Vol. 11.2, E H . l i o d d . E& Elsevier Publishing C o , New I'ork. N Y , 19.58, pp 2 5 - 2 8 , (h) I,. K . Ferguson. " T h e h l o d e r n S t r u c t u r a l T h e o r y o f Organic C h e m i s t r y , ' Prentice-Hall. I n c . , Enplewoods Cliffs, S . J , 1963. pp. 320:326. fa) (a) SI T Rogers. J Arii. C h u m . SOC.,69, 2544 ( 1 9 4 7 j , ( b ) V T. Aleksanian K h E S t e r i n , h l Y u . I-ukiva. I . I. S a f o r o v a . and B 4. K a y o n skii O p l i k a i S p u c l v o s k o p i a , I , 114 (1959). (c) I . 51. K l o t z , J A r m C h u m S o c . 6 6 , 88 (1944:. ( 4 1 (a' I
