THE DIELECTRIC CONTINUUM ASSUMPTION AS A DESCRIPTION OF MEDIUM EFFECTS IN BINARY SOLVENT MIXTURES - IMPLICATIONS FOR ELECTRON-TRANSFER PROCESSES IN COSOLVENT SYSTEMS

Most physical models for solvent effects upon electron-transfer reactions represent the solvent role as a dielectric continuum and incorporate the bulk solvent properties of dielectric constant and/or index of refraction into their solvent-dependent kinetics and thermodynamic terms. Because such models may fail quantitatively when applied to cosolvent mixtures, two isodielectric pairs were used as initial test systems to compare trends in classical continuum functions with changing solvent composition. Particular functions considered included those of Marcus, Kirkwood, Block-Walker, and Brady-Carr; the cosolvent pairs were benzene-CCl4 and nitrobenzene-acetonitrile. The conditions under which the mean-spherical approximation (MSA) model of solute solvation reduces to the simpler continuum models have been investigated.