Positioning solvolyses within the S_N2‐S_N1 and S_N3‐S_N2 spectrum of reaction mechanisms

Abstract

A simple linear regression ( Q equation) is devised to position solvolyses within the established S N 2‐S N 1 spectrum of solvolysis mechanisms. Using 2‐adamantyl tosylate as the S N 1 model and methyl tosylate as the S N 2 model, the equation is applied to solvolyses of ethyl, allyl, secondary alkyl and a range of substituted benzyl and benzoyl tosylates. Using 1‐adamantyl chloride as the S N 1 model and methyl tosylate as the S N 2 model, the equation is applied to solvolyses of substituted benzoyl chlorides in weakly nucleophilic media. In some instances, direct correlations with methyl tosylate were employed. Grunwald–Winstein l values and kinetic solvent isotope effects are also used to locate solvolyses within the spectrum of mechanisms. Product selectivities (S) for solvolyses at 50 °C of p ‐nitrobenzyl tosylate in binary mixtures of alcohol–water and of alcohol–ethanol for five alcohols (methanol, ethanol, 1‐propanol and 2‐propanol and t ‐butanol) are reported and show the expected order of solvent nucleophilicity (RCH 2 OH > R 2 CHOH > R 3 COH). The data support the original assignments establishing the N OTs scale of solvent nucleophilicity. Copyright © 2016 John Wiley & Sons, Ltd.