Stabilities of Carbonium-Ions. IV. Steric Effects in the Solvolysis of Substituted Diphenylmethyl Chlorides

Abstract

The replacement of ortho-hydrogen atoms by methyl groups in diphenylmethyl chloride has three distinguishable results upon the rate of solvolysis . Firstly, the alkyl groupactivates by its electronic effect; secondly, steric interactions diminish all observed substituent effects regardless of the position of the substituent in the aryl system; and thirdly, steric acceleration of the solvolysis can be seen in the rate of reaction of bis (2,6-dimethylphenyl)methyl chloride. The ortho-methyl substituents inhibit the formation of the planar transition state necessary to allow the greatest resonance stabilization by the aryl substituents of the incipient carbocation. Greater degrees of twist are reflected both in the variations in the rates of solvolysis of the poly(orthomethyl ) diphenylmethyl chlorides and in the consistent fall in the value of p⁺ with successive ortho-substitution.