Isomerism and topicity in three- and four-dimensional space: A review

Abstract

Isomerism is a notion of a considerably broad meaning. Not only chemists but also physicists, biologists and philosophers come across it. In the sequel, some basic problems of the contemporary understanding of the phenomenon of isomerism of molecular structures and related problems of topic relationships between homomorphic ligands and faces are dealt with. Illustrating factual material is selected within the domain of organic chemistry. With the rapid development of nomenclature in this area in mind, the issues are presented from a point of view stressing the unity of historical and logical moments. Problems arising when moving from the analysis of molecular structure models towards the analysis of real sets of molecules are highlighted. Differences between the analysis of static molecular structures in three-dimensional space and the analysis of real dynamic molecular structures in four-dimensional space are dealt with in greater detail. The method of NMR spectroscopy is discussed from this standpoint as an example of the most widespread research tool for investigating intramolecular dynamism at present. Stereo-differentiating reactions are also treated briefly and a suggestion is made to introduce into the teaching of isomerism and topicity a classification of differentiating interactions. The relationships discussed are demonstrated comprehensively using the chemical behaviour of an optically active trisubstituted cycloheptatriene-norcaradiene system as an example and, are also discussed in connection with some new findings concerning actual chiral geometries in some conventionally achiral systems. Attention is paid to didactic presentation of the topic and an attempt is made to show probable trends in future development in this domain.