A novel topological index Xu based on the adjacency matrix A and distance matrix D was derived in this paper. The index, which was very easy to calculate and also had good discrimination between isomeric alkanes, was highly correlated with the selected physicochemical properties of alkanes, and most properties were well modeled (r>0.99). Moreover, it was also convenient to extend the Xu index to the multipolybonds, heteroatom-containing compounds using the relative ratio of bond length to C-C bond in place of the adjacent topological distance and the valence δ~i instead of the degree of vertex v~i. The index also produced a fair regression for the heat capacity of olefins and the toxicity and hydrophobicity parameters of alkanols (r>0.99). The calculated values were in good agreement with experimental data. The results suggested that the proposed index with fairly high correlation ability and structural selectivity promised to be a useful parameter in QSPR/QSAR research.

Key words: ORGANIC COMPOUNDS, GRAPH THEORY, ALKANE