NMR INVESTIGATIONS OF THE ENANTIOMERIC EXCESS EFFECTS IN SOLUTIONS WITH WEAK INTERMOLECULAR ASSOCIATION

The main features of statistically controlled associate diasteromerism (SCAD) in solution as measured by nuclear magnetic resonance (NMR) ar e discussed. In an achiral solvent, (R)- and (S)-enantiomers can demon strate distinct NMR signals, with the intensity ratio equal to the con centration ratio, The previous theory of SCADA (anisochronism of nucle ar magnetic moments caused by SCAD) is supplemented by treatment of en antiomeric excess phenomena in relation with the hypothesis that a sam ple consists totally of short-living diastereomeric dimers which are i nvolved in fast (on the NMR time scale) exchange by enantiomers, Therm odynamic parameters of SCAD as well as limits for enantioselectivity p henomena are estimated. (C) 1995 Wiley-Liss, Inc.