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 δH, with π*, and with a linear combination of δH and π*. For nonpolar solutes, only the regression with δHis significant, but for polar solutes the multiple regression with δH, and π* is generally much more satisfactory than either single regression. It is suggested that the term in δH 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 δHis 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 δH 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.