Model calculations of heavy atom isotope effects for E2 and E1cB dehydrochlorination of 1,1-diaryl-2,2-dichloroethanes

Abstract

Calculations of heavy atom kinetic isotope effects for the alkoxide-induced dehydrochlorination of Ar₂CH·CHCl₂ are presented. Previously employed cut-off methods and transition state models are used, and the atoms concerned are α-chlorine (k₃₅/k₃₇ for primary intermolecular and intramolecular effects, and for the secondary effect) and C_α and C_β primary carbon isotope effects, k₁₂/k₁₄). Changes in kinetic isotope effect with simulated variations in transition state structure are discussed. The effect of simulating partial solvation of the incipient anionic leaving group in the transition state is investigated. Theoretical isotope effects are compared with preliminary experimental results, and tentative transition state structures are proposed.