On Structure Descriptors Related with Intramolecular Energy of Alkanes

Abstract

In an earlier work it was demonstrated that the Zenkevich index U provides a measure of the intramolecular energy of an organic molecule, and that– in the case of alkanes– it is related to the Wiener index. We now show that U is much closer related to the recently introduced variable Wiener index Wλ: Within sets of isomeric alkanes, the relation between U and Wλ is linear, the (U,Wλ)-points forming several, mutually parallel, lines. Each such line pertains to a group of isomers possessing a fixed number of methyl groups. There exists a critical value of the parameter λ for which all the (U,Wλ)-lines coalesce, in which case the relation between U and Wλ becomes independent of the number of methyl groups. Approximate analytical expressions for the (U,Wλ)-dependence are deduced.