INTERPRETATION OF A GENERAL SCALE OF SOLVENT POLARITIES - SIMPLIFIED REACTION FIELD-THEORY MODIFICATION

The existence of linear relationships of good quality involving the effects of polar solvents on different properties of neutral, highly polar solutes is rationalized in terms of the reaction field theory. It is shown that the treatment of Block and Walker in which the dielectric constant at a distance r from the center of the solute cavity is taken as ε(r) = εBe-K/r where εB is the bulk dielectric constant, gives a satisfactory description of experimental results involving NMR shift data, solvation free energies, activation free energies, π-π* transitions, and molecular dipole moments. It is concluded that (1) the short-lived clustering of polar solvent molecules around dipolar solutes is a significant factor to be considered in the study of solvent effects on dipolar solutes; (2) the scope of the reaction field formalism can be extended to solutes of high polarity provided allowance is made for dielectric saturation of the polar solvent molecules. © 1979 American Chemical Society.