Crystallographic consequences of molecular dissymmetry.

The molecular chirality associated with an optically active molecule is manifested in the bulk crystallography of the compound. The historical development of optical activity was greatly aided by systematic studies of the habits of enantiomorphic crystals. The concepts of molecular dissymmetry, crystallography, and chirality are therefore linked. Racemic materials can be characterized by means of their melting-point phase diagrams, and this information used to design rational separations of racemic mixtures into their component enantiomers. Certain compounds are found to resolve spontaneously upon crystallization, and the enantiomers of these conglomerate species may be separated by direct crystallization. Compounds which crystallize as true racemates require resolution through the formation and separation of dissociable diastereomer species. The choice of resolution pathway is therefore determinable through an evaluation of the melting-point phase diagrams. When possible, resolution through direct crystallization represents the simplest, most cost-effective means of enantiomer resolution.