PI index of extremal simple pericondensed hexagonal systems. (Q2846619)

The Padmakar-Ivan index is a Wiener-Szeged-like topological index which reflects certain structural features of organic molecules. This paper deals with the study of the PI index with respect to the extremal simple pericondensed hexagonal system. It turned out that the PI index has a similar discriminating function as the Wiener index or the Szeged index, sometimes it gave better results. Some authors reported on a quantitative structure-toxicity relationship study by using the PI index. However, the PI index alone is not an appropriate index for modeling toxicity of nitrobenzene derivatives. Combining the PI index with other distance-based topological indices resulted in statistically significant models and excellent results were obtained in pentaparametric models.