Chromatographic behaviour of diastereoisomers : X. Thin-layer chromatographic retentions on silica of some ( E)- and ( Z)-oxazolones and related cinnamates as a function of mobile phase effects or Hammett constants

Abstract

The thin-layer chromatographic behaviour of twenty diastereoisomeric 1,1-disubstituted 2-arylethenes [( Z)- and ( E)-oxazolones and -cinnamates] on silica was studied using 40 mobile phases. The ( E)-oxazolone and the ( Z)-cinnamate were the stronger adsorbing isomers in all instances. The relative retentions and the retentions themselves were correlated with solvent selectivity effects or Hammett constants of the various substituents on the aryl group. Solvent selectivity effects were approximated on the basis of Snyder's theory by the parameter localization, m, for experiments with mobile phases of constant strength, ε, and by the molar fraction of one of the solvents for the experiments with binary mobile phases of increasing ε. According to the data obtained, electronic effects determine the model of adsorption of any Z/E pair and steric effects modify it, controlling the relative retention which is not affected by solvent selectivity effects and the nature of the aryl group.