Development of a generalized model for the π* scale of solvent polarity

The Kamlet-Taft π* scale of solvent dipolarity/polarizability is examined with a model that combines the classical Onsager reaction field and the dielectrically saturable Block and Walker reaction field. The model presented is found to adequately correlate the π* values of a wide range of solvent classes (perfluoro, polychlorinated, aromatic, and dipolar aprotic); however, systematic deviations are observed for polychlorinated solvents. Comparison of results obtained for 76 aprotic low-molecular-weight solvents with the results for a series of methyl/phenylsiloxane polymer solvents supports the general approach outlined.