A critical view on the Lewis-donor (nucleophilic) properties of solvents

Parameters which claim to reflect the Lewis-type donor properties of solvents are reviewed. It will be shown that the original concept of Lewis, where one partner supplies one electron-pair for a chemical bond and the other partner accepts this electron-pair, is limited to "hard-hard" interactions. "Soft-soft" interactions, where both solute and solvent donate and accept electron pairs cannot be accounted for by parameters derived from model substances, which are based on the classical Lewis concept. Disregard of the different chemical behaviour of "hard-hard" and "soft-soft" interactions has led to misinterpretation of solvent parameters and to deviations in correlations of kinetic and thermodynamic properties with solvent parameters.