Discriminating Interactions Between Chiral Molecules In the Liquid-phase - Effect On Volumetric Properties

Volume changes on mixing for binary mixtures of optically active liquid compounds have been determined at 25 "C by using a vibrating tube densimeter. Six enantiomeric and six nonenantiomeric pairs of chiral molecules have been considered. In all the cases chiral discrimination appeared to produce small but significant effects (0.0024.016 cm3 mol-'). The excess molar volumes, p, of the (+) and (-) isomers of limonene, carvone, 2-methyl-1-butanol, and a-methylbenzylamine showed negative values, while VE of the enantiomers of a-pinene and 2-odanol gave positive results. Partial molar volumes, Po,fo r the investigated chiral solutes in chiral solvents have been obtained from p data. The effecta of chiral discrimination of Po have been compared with the prediction of a simple statistical approach in which discrimination arises from space-filling differences in contacts between hard surfaces.