Solvent Effects on the Solvolysis of Neophyl Tosylates

Abstract

Abstract Solvolysis rates of 2-phenyl-2-methylpropyl and 2-(p-methoxyphenyl)-2-methylpropyl p-toluenesulfonates were determined in a wide variety of solvents and the solvent effects were analyzed based on the Winstein–Grunwald equation. The solvent effect on neophyl solvolyses failed to give a single linear correlation with the 2-adamantyl YOTs parameter. There was dispersion behavior for the respective binary solvent series between neophyl kΔ substrates and 2-adamantyl tosylate. The pattern of dispersion could not be interpreted in terms of nucleophilic solvent assistance. The response to the solvent polarity (m value for each binary solvent series) was significantly lower for both the methoxy and the unsubstituted derivatives than the m = 1.0 for the limiting kc solvolysis, and appreciably lower for the methoxy derivative than for the unsubstituted one. Linearity of the solvent effects between both neophyl systems and also between other kΔ substrates implied the existence of a unique kinetic solvent polarity scale YΔ characteristic of the β-aryl-assisted (kΔ) solvolysis. The dispersion behavior and reduced m value for the kΔ solvolysis were compatible with the entire π-delocalization of cationic charge between the assisting aryl-ring and the reaction center in the transition state.