Do gas-phase reactions between alcohols and protonated alcohols proceed through SN2 transition states? An ab initio study

Abstract

Ab initio calculations (GAUSSIAN 82, SCF 4-31G) indicate that methanol can react with protonated methanol to form two initial intermediates. The minor route produces a species where the methanol oxygen is hydrogen-bonded to the methyl hydrogen atoms of Me[graphic omitted]H²; the major route involves formation of a hydrogen bond between the methanol oxygen and an oxonium hydrogen to produce an unsymmetrical bismethanolhydrogen (1+) ion. Both initial intermediates react further to form the dimethyl oxonium ion plus water: the former reaction proceeds efficiently through an S_N2 transition state, the latter by a less efficient process involving the same S_N2 transition state.