Positioning solvolyses within the SN2-SN1 and SN3-SN2 spectrum of reaction mechanisms

A simple linear regression (Q equation) is devised to position solvolyses within the established SN2-SN1 spectrum of solvolysis mechanisms. Using 2-adamantyl tosylate as the SN1 model and methyl tosylate as the SN2 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 SN1 model and methyl tosylate as the SN2 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 (RCH2OH > R2CHOH > R3COH). The data support the original assignments establishing the NOTs scale of solvent nucleophilicity. Copyright © 2016 John Wiley & Sons, Ltd.