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The Origin of Regioselectivity in a-Cleavage Reactions of Cyclopropenethiones: Potential Role of Pseudo-Jahn-Teller Effect in Substituted Cyclopropenyl Systems

Usha, G and Rao, BNageswer and Chandrasekhar, Jayaraman and Ramamurthy, V (1986) The Origin of Regioselectivity in a-Cleavage Reactions of Cyclopropenethiones: Potential Role of Pseudo-Jahn-Teller Effect in Substituted Cyclopropenyl Systems. In: Journal of Organic Chemistry, 51 (19). pp. 3630-3635.

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Official URL: http://pubs.acs.org/doi/abs/10.1021/jo00369a015

Abstract

Arylalkylcyclopropenethiones undergo highly regioselective photochemical a-cleavage via thioketene carbene intermediates, giving rise to products derived from the less stabilized carbene. UHF MIND0/3 calculations provide an insight into this unexpected regioselectivity. The nx* triplet of cyclopropenethione is calculated to have a highly unsymmetrical geometry with an elongated C-C bond, a delocalized thiaaUyl fragment, and a pyramidal radicaloid carbon (which eventually becomes the carbene center). From this molecular electronic structure, aryl group stabilization is expected to be more effective at the thiaallyl group rather than at the pyramidal radical center. Thus, the stability of the substituted triplet thione rather than that of the thioketene carbene determines the preferred regiochemistry of cleavage. The unusual structure of the cyclopropenethione triplet is suggested to be related to one of the Jahn-Teller distorted forms of the cyclopropenyl radical. An alternative symmetrical structure is adopted by the corresponding triplet of cyclopropenone, partly accounting for its differing photobehavior. A similar structural dichotomy is demonstrated for the corresponding radical anions as well.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Chemical Sciences > Organic Chemistry
Date Deposited: 03 Feb 2010 09:53
Last Modified: 19 Sep 2010 05:35
URI: http://eprints.iisc.ernet.in/id/eprint/20901

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