Design of Topological Indices. Part 10.1 Parameters Based on Electronegativity and Covalent Radius for the Computation of Molecular Graph Descriptors for Heteroatom-Containing Molecules

Two new approaches are presented for the calculation of atom and bond parameters for heteroatom-containing molecules used in computing graph theoretic invariants. In the first approach, the atom and bond weights are computed on the basis of relative atomic electronegativity, using carbon as standard. In the second system, the relative covalent radii are used to compute atom and bond weights, again with the carbon atom as standard. The new definition of the atom and bond parameters leads to a periodic variation versus the atomic number Z, with a more natural variation when compared with the parameters defined only by Z. The two approaches are used to define and compute topological indices based on graph distance. A quantitative structure-property relationship study is reported for boiling points of 185 acyclic compounds with one or two oxygen or sulfur atoms (devoid of hydrogen bonding), in terms of four or five molecular descriptors.