Solvation and nucleophilic reactivity of 2-nitrobenzoate and of 2,6-dichlorobenzoate ions in acetonitrile–methanol mixtures

Abstract

Rate constants and activation parameters for the reactions of the 2-nitrobenzoate and 2,6-dichlorobenzoate ions with ethyl iodide have been determined in acetonitrile–methanol mixtures. The activation parameters for the two reactions indicated different responses to solvent compositions. Single-ion enthalpies of transfer for the two anions have also been determined in the same solvent mixtures and on the basis of the results single-ion enthalpies of transfer for the transition-state anion for the two reactions have also been calculated and separated into their components. By empirical analysis of the transfer enthalpies due to the “more physical” interaction for the transition-state anion, Δ_tH_PHYS^AN→MeOH (TS⁻), the approach of solvent molecules to the α-carbon atom and the central carbon atom in carboxylate group in the carboxylate ion, together with the number of partial dipoles in the anion, have been suggested to account for the various transfer enthalpies.