Differentiations of Enantiomers via Their Diastereomeric Association Complexes—There Are Two Ways of Shaking Hands

The intermolecular interactions of one enantiomer with a chiral auxiliary molecule and the interactions of the other enantiomer with the auxiliary are considered. Different functions of the latter give rise to the following well-known aspects of organic stereochemistry that are characterized in the present article: (i) preparative separation of enantiomers via crystallization of diastereomeric salts; (ii) analysis of enantiomers by NMR spectroscopy; (iii) separation of enantiomers by chromatography; (iv) biological activities of enantiomers; and (v) reactivities of enantiomers in enzymatic resolution. The common basis of these aspects is the formation of two diastereomeric association complexes that may differ with respect to their physical and chemical properties. The following practical applications of this phenomenon are briefly described: the small- and large-scale preparation of the enantiomers of organic compounds; the analysis of chiral nonracemic mixtures by chromatography and by NMR spectroscopy; and the growing use of drugs in the form of one of the enantiomers. It is proposed to emphasize the similarity of the association-based differentiations. This goal can be attained by giving a corresponding lecture in the second or third year of university chemistry.