Fully optimized calculation and frequency analysis of 209 polychlorinated diphenyl ether (PCDE) compounds were carried out using DFT method at the B3LYP/6-31G* level and their structural and thermodynamic parameters were obtained. The relation of these parameters with number and position of Cl atom substitution (N_PCS) was studied and it was found that there existed high correlation between molecular mean polarizability (α), enthalpy (H^Ө), free energy (G^Ө), heat capacity at constant volume ( ) or entropy (S^Ө) and N_PCS (correlative coefficients being 0.9955, 1.0000, 1.0000, 0.9918 or 0.9995 respectively). It was also found that molecular volume (V_m) and the energy of the highest occupied molecular orbital (E_HOMO) have good correlation with N_PCS and correlative coefficients r² were 0.9735 and 0.9362 respectively. The isodesmic reactions were designed to calculate standard enthalpy of formation (Δ_fH^Ө) and standard free energy of formation (Δ_fG^Ө) of PCDE congeners. The order of relative stability of PCDE congeners was theoretically proposed based on the relative magnitude of their Δ_fG^Ө.

Key words: polychlorinated diphenyl ether, density functional theory (DFT), position of Cl atom substitution, structural parameter, thermodynamic property, relative stability