Nucleophilic substitution reactions of aliphatic and aromatic carboxylate ions with ethyl iodide. Specific interactions and isokinetic relationships in acetonitrile–methanol mixtures

Abstract

Transfer enthalpies for the transition-state anions in the reactions of the carboxylate anions adamantane-1-carboxylate, pivalate, benzoate, and 4-nitrobenzoate with ethyl iodide have been determined in acetonitrile–methanol mixtures (AN–MeOH). After the separation of these enthalpies into their constituent terms, i.e., physical interaction and specific interaction enthalpies, the number of methanol molecules hydrogen-bonded to the anion has been evaluated on the basis of the assumption that the isokinetic relationship is realized between activation parameters, which can be identified as physical interaction quantities. An empirical correlation was observed between that number and the specific interaction enthalpy, ΔH_t,SI^AN→MeOH, for the anion. On the basis of the AM1 model calculations, discussion is given on the factors which affect the physical interaction enthalpy.