Linear solvation energy relationships. Part 19. Correlation of the free energies of solution of 41 solutes in select solvents with Hildebrand's solubility parameter, δH, and with the solvatochromic parameter, π*

Abstract

The effect of a series of select solvents on the standard free energies of solution of 34 volatile solutes and on the standard free energies of transfer of 7 involatile solutes has been correlated with δ_H, with π*, and with a linear combination of δ_H and π*. For nonpolar solutes, only the regression with δ_His significant, but for polar solutes the multiple regression with δ_H, and π* is generally much more satisfactory than either single regression. It is suggested that the term in δ_H represents the solvent-solvent interaction that has to be overcome in order to create a suitably sized cavity in the solvent. Indeed, the value of the coefficient in δ_His directly proportional to the size of the (nonpolar) solute. It is also suggested that the term in π* represents the mainly dipolar–dipolar solute–solvent interaction; thus the coefficient in, π* is related, though not linearly, to the solute dipole moment or charge separation. Use of the combination of δ_H and, π* thus enables the solvent effect on the free energies of a very wide range of solutes to be correlated and interpreted in a conceptually simple manner.