Impact of chirality on phase diagrams and conversely relative quantification of chirality by using the binary phase diagram of enantiomers

Abstract

The heterogeneous equilibria between two enantiomers can be depicted in a unary system or a binary system according to the possibility of interconvertion (n = 2 if no racemization occurs). In case of a binary system, the symmetry between the chemical potentials introduces a modification in the Gibbs phase rule but the resulting Gibbs-Scott phase rule is only applicable if the number of symmetrical phases differs from zero i.e. no racemic monophasic domain exists. At a given temperature a quantitative determination of the degrees of asymmetry of a molecule is proposed by using the stable (or metastable) binary heterogeneous equilibria with its antipode. For monophasic domains, this evaluation is based on the width in composition and on how far from the racemic mixture the boundaries are. For biphasic domains the evaluation corresponds to the algebraic departure in composition of the two co-existing phases.