The origin of regioselectivity in α-cleavage reactions of cyclopropenethiones

Potential role of Pseudo-Jahn-Teller effect in substituted cyclopropenyl systems

G. Usha, B. Nageswer Rao, J. Chandrasekhar, Vaidhyanathan Ramamurthy

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

Arylalkylcyclopropenethiones undergo highly regioselective photochemical α-cleavage via thioketene carbene intermediates, giving rise to products derived from the less stabilized carbene. UHF MINDO/3 calculations provide an insight into this unexpected regioselectivity. The nπ* triplet of cyclopropenethione is calculated to have a highly unsymmetrical geometry with an elongated C-C bond, a delocalized thiaallyl 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.

Original languageEnglish
Pages (from-to)3630-3635
Number of pages6
JournalJournal of Organic Chemistry
Volume51
Issue number19
StatePublished - Dec 1 1986
Externally publishedYes

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Jahn-Teller effect
Regioselectivity
Thiones
Molecular electronics
Molecular structure
Electronic structure
Anions
Carbon
Stabilization
Geometry
carbene

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

The origin of regioselectivity in α-cleavage reactions of cyclopropenethiones : Potential role of Pseudo-Jahn-Teller effect in substituted cyclopropenyl systems. / Usha, G.; Rao, B. Nageswer; Chandrasekhar, J.; Ramamurthy, Vaidhyanathan.

In: Journal of Organic Chemistry, Vol. 51, No. 19, 01.12.1986, p. 3630-3635.

Research output: Contribution to journalArticle

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