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 Keq, 31·9 and 34·9 kcal mol–1 for Ea, 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 Ea 25 kcal mol–1 and ΔS‡–9·7 cal K–1 mol–1 for the diequatorial–diaxial interconversion. Possible interpretations are discussed.