Solutions of organic solutes. Part 2.—Moderately polar compounds in water; limiting volumes and compressibilities

Abstract

The chemical thermodynamic (CT) model used to develop equations for the partial molal volumes and compressibilities of amino acids (J. V. Leyendekkers, J. Phys. Chem., 1986, 90, 5449) has been applied to moderately polar solutes; eight solids and 22 liquids. Radii and packing distances of the solutes in water have been estimated from the scaled particle theory, for 25 and 5 °C. The space requirements of the solute due to its polar character could then be deduced from the CT model. These results plus an analysis of the compressibilities indicated that the polar interactions are linked to dynamic correlations between the solute and water and have only a small effect on the volume changes. The latter are dominated by the geometric packing effects. Clathrate-like local bonding is implied, with solute to water ratios of 1:17 and 1:28 (for the bulkier solutes). The overall results are in accord with deductions from computer simulations and a variety of experimental data (e.g. Raman, X-ray and 17O n.m.r. techniques).