APPROACHES TO THE PROBLEMS OF SOLVATION IN PURE SOLVENTS AND PREFERENTIAL SOLVATION IN MIXED-SOLVENTS

Of paramount importance to the understanding of the behaviour of solutes in solvent media is the problem of solute-solvent interaction (solvation), or, in solvent mixtures, of solvent-sorting in the solvation sphere of the solute (preferential solvation). Different techniques and theoretical approaches have been developed but the relation of these to classical thermodynamics has rarely been critically discussed. Theories of solute-solvent interaction can be broadly divided into continuum models and models which acknowledge the molecular nature of the solvent. In the latter, the arrangement of the solvent is often treated in terms of discrete structure only in the solvation sphere, or, more generally, through distribution functions which can be obtained in principle from X-ray and neutron scattering experiments. Unfortunately theoretical approaches based on the nature and extent of intermolecular forces have not yet reached the state of development, in spite of the power of modern high speed computers, that they can be of real use in interpreting the properties of systems of experimental and technological importance. By highlighting the interrelations between the different approaches, the possible origin of some recently reported discrepancies in the interpretation of systems studied by two or more experimental methods may become apparent. © IUPAC