Graphical bond orders: Novel structural descriptors

We outline an algorithm for construction of novel molecular descriptors from known structural invariants or molecular properties viewed as descriptors. The novel descriptors are bond-additive quantities derived by assigning to each bond a contribution x’obtained by evaluating invariant X for graph G’-e, which is attained from graph G (representing a given molecule) by deleting edge e. The molecular descriptor X’/X is obtained as a normalized sum of bond contributions, where X’is equal to the sum of bond orders x’. The approach is illustrated by presenting X’/X descriptors for smaller alkanes for several well-known topological indices, including the connectivity index, Hosoya’s Z index, the Wiener index, and others. The algorithm is quite general and allows one to include molecular properties as source data for the construction of novel descriptors. This is particularly important in view of a limited number of properties used as descriptors in traditional quantitative structure-activity studies. The new algorithm literally doubles thenumber of descriptors available to traditional chemometricians in their quest for novel property-activity relationships.