EXTENSION OF THE FRONTIER REACTIVITY INDEXES TO GROUPS OF ATOMS AND APPLICATION TO QUANTITATIVE STRUCTURE-ACTIVITY RELATIONSHIP STUDIES

The concept of frontier reactivity index, proposed by Fukui et al. (J. Chem. Phys., 20 (1952) 722), was extended to groups of atoms. The pur pose of this procedure is to simulate frontier indices capable of pred icting the susceptibility of a chemical group to an external electroni c interaction, such as nucleophilic, electrophilic or radical. The gro up frontier indices can be useful in quantitative structure-activity r elationship (QSAR) studies, where substituent constants for groups of atoms are widely used. The group frontier indices are obtained through the sum of the corresponding atomic frontier indices. The atomic fron tier indices were computed from AM1 wavefunction coefficients. The fro ntier indices considered in this article, i.e. frontier electron, orbi tal and radical densities, are shown to be relatively independent of t he molecular geometry. We applied the group frontier index concept to a QSAR study of triazene derivatives. The group frontier indices that appear to be significant in the correlation analysis are consistent wi th the known hydroxylation mechanism of triazene induced mutagenesis.