Solvolysis rates of diarylmethyl p-nitrobenzoates in aqueous ethanol. The question of solvent assistance and the validity of selectivity probes

Abstract

Rate constants for solvolysis of diarylmethyl p-nitrobenzoates in ethanol–water and trifluoroethanol–water mixtures have been measured. Hammett ρ values and Winstein–Grunwald m parameters have been evaluated. The former are insensitive to solvent composition and the latter to ring substituent. Mechanistic speculation is regttired before these results can be assessed as contributors to debate on the reactivity–selectivity principle, and it is concluded, on the basis of the trifluoroethanol–water probe, that solvent assistance is absent.