The thermodynamic properties of 76 polyfluorinated dibenzo-p-dioxins (PFDDs) in the ideal gas state at 298.15 K and 1.013×10⁵ Pa have been calculated at the B3LYP/6-311G** and B3LYP/6-31G* levels using Gaussian 03 program, and it was found that values of standard enthalpy of formation (Δ_fH^?), standard free energy of formation (Δ_fG^?) and standard entropy (S^?) were broadly consistent under the two base groups. According to the relative magnitude of their Δ_fG^? at the B3LYP/6-311G** level, the relative stability order of PFDD congeners was theoretically proposed. Octanol-water partition coefficients (lg K_ow) of polybrominated dibenzofurans (PBDDs), polychlorinated dibenzofurans (PCDDs) and PFDDs were calculated by group contributions. Comparison of the properties (including lg K_ow, S^?, Δ_fH^? and Δ_fG^?) between PFDDs and PCDDs, PBDDs was carried out. Moreover, the relative rate constants of formation reactions of PFDDs and the values of molar heat capacity at constant pressure (C_p,m) from 200 to 1800 K for PFDDs congeners were calculated using a statistical thermodynamics calculation program. The temperature dependence relation of C_p,m was obtained using the least-squares method. The result shows that there exists very good relationship between C_p,m and temperature (T, T^－1 and T^－2) for almost all PFDD congeners.

Key words: polyfluorinated dibenzo-p-dioxins, DFT method, thermodynamic property, octanol-water partition coefficient (lg K_ow), molar heat capacity at constant pressure (C_p,m)