Solvolysis of 2-aryl-2-adamantyl p-nitrobenzoates and some tertiary benzylic p-nitrobenzoates. Y_BnOPNB and Y_xBnOPNB scales

Solvolysis rate constants for a number of tertiary benzylic p-nitrobenzoate esters in a wide range of solvents were measured. New scales of solvent ionizing power for Grunwald-Winstein-type correlation analyses, Y_BnOPNB from 2-phenyl-2-adamantyl p-nitrobenzoate and Y_xBnOPNB from 2-(6-methoxy-2-naphthyl)-2- adamantyl p-nitrobenzoate, were developed for the mechanistic study of solvent effects on the solvolytic reactivity of benzylic p-nitrobenzoates. The excellent linear log k - Y_BnOPNB plot for 2-(4-methylphenyl)-2-propyl p-nitrobenzoate indicated a limiting S_N1 mechanism. The solvolytic transition state for 9-phenyl-9-fluorenyl p-nitrobenzoate and that for 1,1-diphenylethyl p-nitrobenzoate were considered to involve extended positive charge delocalizations from the observation of linear relationships between log k and Y_xBnOPNB. The ambiguity in the case of 2, 2-dimethyl-1-(4-methoxyphenyl)-1-phenyl-1-propyl p-nitrobenzoate is discussed.