Thermal equilibration of substituted trans-1,2-dibromocyclohexanes

Abstract

The kinetics of the thermal equilibration of five trans-1,2-dibromocyclohexanes carrying substituents in the 3- or 4-position have been measured at different temperatures and the activation parameters have been determined. Values ranging between 1·64 and 2·70 for K_eq, 31·9 and 34·9 kcal mol^–1 for E_a, and –1·3 and +5·3 cal K^–1 mol^–1 for ΔS‡ have been found for the 3-methyl, 4-methyl, 4-t-butyl, and 4-methoxycarbonyl derivatives. The 3-t-butyl derivative deviates considerably, since it gives more than 99% of the diaxial isomer at equilibrium and has E_a 25 kcal mol^–1 and ΔS‡–9·7 cal K^–1 mol^–1 for the diequatorial–diaxial interconversion. Possible interpretations are discussed.