Solutions of organic solutes. Part 4.—Structure and the effect of solute concentration on the volume

Abstract

The chemical thermodynamic (CT) model and dielectric theory have been used for an analysis of [∂(∂V/∂n₂)/∂n₂]_{T, p, n}, the volume differential with respect to solute concentration, for aqueous solutions of dipolar compounds at 25 °C (24 solutes). There are three main components of this function, arising from: (1) the response of the solute-cavity volume (including packing and dynamic requirements) to changes in concentration, (2) changes in the dipole compressional effects and (3) the change in the static-dielectric orientational correlation function (g₁) of the solvent, water. For the amino acids the third term is negligible. The orientational correlation functions of the solute (g₂) and solvent were estimated and considered in relation to electrical packing factors, the cavity field and the polar work associated with solvation. The relationship of g₂ to the number of adjacent water molecules showed distinct solute classifications in terms of the relative effects on orientation and relaxation of neighbouring water molecules.