Quantitative structure-property relationship study of GC retention indices for PCDFs by DFT and relative position of chlorine substitution

The structural property and thermodynamic parameters of 136 polychlorinated dibenzofurans (PCDFs) were obtained by fully optimized calculation at B3LYP/6-31G* level, and the free energy and standard heat of formation of these compounds were consequently obtained by designing isodemic reactions. The dependency of these parameters on the number and position of chlorine substitutions were further discussed. The specific structural and thermodynamic parameters were consequently taken as chemical descriptors to get theoretical model I for predicting the gas chromatographic retention indices (RI) of PCDF congeners (R2=0.993 and SD=23.7 and q2=0.986), in which the maximum relative error of RI for PCDFs is 2.75%. On the other hand, the number and relative position of chlorine substitutions were also used as theoretical descriptors, and the corresponding RI prediction model II (R2=0.997, SD=15.1 and q2=0.997) for PCDFs was thus achieved. With maximum error of only 1.42% in predicting RI, it was surprisingly found that model II is simple and has high precision and predictive power. Finally validation for two models was carried out and the result showed the models developed in the present study are both reliable.