Nuclear magnetic resonance (NMR) spectroscopic investigation of interaction energies of ephedrine stereoisomers in noncrystalline solids and its correlation with thermodynamic data

Abstract

Equations relating the interaction energies of each of the binary mixtures of ephedrine from linear combinations of the energies of the individual isomers are presented. The interaction energies in the noncrystalline solid mixtures measured from NMR chemical shift data using cross-polarization magic angle spinning nuclear magnetic resonance 13C cross-polarization magic angle spinning nuclear magnetic resonance (13CP/MAS NMR) spectroscopy correlate strongly with interaction energy from thermodynamic data. The summation of changes in relative frequencies for structurally equivalent carbons is used as a measure of differences in electron shielding on mixing. The relative direction of polarization of individual stereoisomers is found to affect association in noncrystalline binary mixtures of solids. NMR chemical shift data of solids may be useful in confirming spectroscopically the interactions of stereoisomers observed thermodynamically.