Substituent effects in saturated systems. Conformationally transmitted retardation of the rates of solvolysis of substituted cyclohexyl-phenylmethyl chlorides

Abstract

Rate coefficients at several temperatures have been measured for the solvolysis in aqueous acetone of the methyl chlorides p-RC₆H₄·CHCl·C₆H₁₁ and trans-4-RC₆H₁₀·CHClPh where R = H, Me, and Bu^t. The products of solvolysis of cyclohexyl-p-tolylmethyl chloride have been identified and their relative proportions determined.

Alkyl substituents in the cyclohexane ring retard the rate as much as substitution in the phenyl ring increases it. Analysis of activation parameters shows that the remote t-butyl group in the alicyclic ring exerts a rate-increasing effect on the enthalpy of activation as well as an over-riding rate-decreasing effect on the entropy of activation. Both are rationalised on the basis of ring deformation by the t-butyl substituent.