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Optimized calculation of 209 PCBs was carried out at B3LYP/6-31G* level in Gaussian98 program to obtain their structural parameters. It was found there is significant correlation between the Cl substitution position and some structural parameters such as a (r 2 ¼ 0.9972), E HOMO (r 2 ¼ 0.8874) etc. Consequently the numbers of Cl substitution positions (N) were taken as theoretical descriptors to establish the novel QSPR model for predicting n-octanol/water partition coefficients (logK ow ) of all PCB congeners, which can be used directly without computation of their complex structural and thermodynamic parameters. The new model achieved in this work contains three variables, of which r 2 ¼ 0.9497 and q 2 ¼ 0.9465. In addition, the variation inflation factors (VIF) of variables in the present model are all less than 5.0, suggesting high accuracy of the logK ow predicting model. And the results of cross-validation test and method validation (r 2 ¼ 0.9640 and q 2 ¼ 0.9606) also showed the models of this study exhibited optimum stability, convenience for use and better predictive power than that from AM1 method.

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