Topicity and Stereogenicity

Since the terminology in stereochemistry has been to a great extent empirically developed, it has not escaped some ambiguity. Thus, there have appeared many reviews for clarifying or getting rid of such ambiguity.[1]–[7] The term stereogenic was originally proposed by McCasland[8] in order to avoid confusions provided by so-called “asymmetric” and “pseudoasymmetric” carbon atoms. The term stereogenic has been utilized as a key concept in the revised CIP-system for describing chirality and related matters. [9] Later, Mislow and Siegel[10] have extended the definition of a stereogenic atom so as to manipulate a stereogenic element (unit); this is defined as an element (uint) bearing several groups of such nature that an interchange of two groups produces a stereoisomer. They also discussed the conceptual distinction between the stereogenicity and chirotopicity. The term stereogenic has been adopted by several authors[11] in place of the terms “asymmetric” and “chiral”. In the present chapter, we redefine topicity terms in the light of chirality fittingness of orbits and then discuss stereogenicity.