https://doi.org/10.1351/goldbook.11525
A numerical value associated with chemical constitution for correlation of chemical structure with various physical properties, chemical reactivity or biological activity. The numerical basis for topological indices is provided (depending on how a molecular graph is converted into a numerical value) by either the adjacency matrix or the topological distance matrix. In the latter the topological distance between two vertices is the number of edges in the shortest path between these.
Examples: Molecular connectivity chi (\(^{m}X_{t}\)); Kappa Shape (\(^{1}K\), \(^{2}K\), \(^{3}K\), etc.); electrotopological state (\(S_{i}\)); and Dragon descriptors.