Determination of enantiomer separation factors by nuclear magnetic resonance spectroscopy and by chiral liquid chromatography

The equilibrium constants K+ and K− for formation of the diastereomeric complexes of the two enantiomers of O,O′-dibenzoyltartaric acid (DBTA) with the chiral selector N,N′-diallyltartardiamide bis-(4-tert.-butylbenzoate) (TBB) have been determined by 1H-NMR. The experiments were performed at different temperatures in CDCl3 or in cyclohexane-d12/2-propanol-d8 mixtures. The equilibrium constants from the 1H-NMR results have been compared with the retention factors (k′) obtained from the chromatographic resolution of rac. DBTA on a Kromasil CHI–TBB column with the same solvents as mobile phases. A satisfactory correlation between the 1H-NMR data and the chromatographic data was found.