Solvation of carboxylate ions and of transition-state anions for the reaction of carboxylate ion with ethyl iodide in acetonitrile–methanol mixtures. Thermodynamic and quantum mechanical approaches

Abstract

Rate constants and activation parameters for carboxylate ion plus ethyl iodide reactions and enthalpies of solution for the tetraalkylammonium salts of relevant nucleophiles have both been measured in acetonitrile–methanol mixtures and have been analysed from the viewpoint of molecular thermodynamics of solute–solvent interaction. An empirical correlation incorporating nucleophiles and transition-state anions has been found between the derived quantities, namely the specific interaction enthalpies for anions and the number of methanol molecules participating in hydrogen bonding with the anions. The mechanism of the hydrogen-bonding interaction in the transition state could be visualized through rationalization of the specific interaction enthalpies for the transition-state anions in terms of the concept of the ‘effective atomic charge on oxygen’.