Nuclear magnetic resonance spectra, configuration and conformation of diastereomers: 3-Substituted 2,3-diphenylpropanoic acids and their methyl esters

Abstract

The NMR spectra of the erythro and threo forms of compounds of the type PhCH AXCH B(Ph) COOR, where X = OH, OAc, NH 2, NHMe, NHPh, NHCONH 2, NHCONHAc, and R = H or Me have been investigated in CDCl 3 and DMSO-d 6 solutions at normal and in some cases also at higher temperature. The values of the vicinal coupling constant J AB are used to study the conformational equilibrium of the erythro and threo forms and its dependence on the solvent and temperature. It is shown that the chemical-shift difference and the shape of the signals of some proton groups as R = Me and Ph are criteria permitting an unequivocal assignment of relative configuration of diastereomers of such type as well as their quantitative determination in complex mixtures.