Preferential enrichment and crystal structure

Comparison of three different stable crystal structures of (+/-)-[2-[4-(3-e thoxy- 2-hydroxypropoxy)phenylcarbamoyl]ethyl]dimethylammonium p-nitrobenze nesulfonate [(+/-)-NNMe2], and its p-chlorobenzene-sulfonate [(+/-)-NCMe2] and p-toluenesulfonate [(+/-)-NTMe2] derivatives is described. The first tw o racemates exhibited the phenomenon of the Preferential Enrichment, but th e last one failed to do, It is clear that the nature of the para substituen t on the benzenesulfonate group greatly affects the crystal structure and t hereby governs the occurrence of the Preferential Enrichment; i.e., substit ution by an electron-withdrawing group leads to the formantion of an ordere d racemic compound crystal or a fairly ordered racemic mixed crystal of the two enantiomers. while the presence of an electron-donating group results in the formation of a highly disordered racemic mixed crystal.