One of the subjects of special interest in chemical structure handling is to be able to associate a unique quantitative value to each and every chemical compound. The job is not only huge from the stand point of the number of compounds known and to be known, but quite difficult as well from the angle of developing a suitable method. One of the common situations is to be able to discriminate isomeric structures where a large number of compounds having closely related structures for same number of atoms come into picture and this number grows very fast as the number of atoms increases. Getting quantitative descriptors having power of discriminating one compound from another is an important requirement for storage, retrieval and handling of chemical structures as well as for predicting molecular properties/activities. In this chapter, we review several molecular descriptors, mostly topological distance based, in the form of topological indices considering the connectivity aspect of molecular structures only, that have useful discriminative power.
Keywords: Chemical documentation, discrimination of graphs, distance based topological index, distance sum, graph distance complexity, graph vertex complexity, information content of a graph, information-theoretical topological index, molecular connectivity, molecular graph, paths in a graph, spectra of graph, structure property/activity analysis, topological distance, topological index.