The thermodynamic properties of 135 polychlorinated carbazoles (PCCZ) in the ideal gas state at 298.15 K and 1.013×105 Pa have been calculated at the B3LYP/6-31G* level using Gaussian 03 program. The isodesmic reactions were designed to calculate the standard enthalpy of formation (ΔfHÖ) and standard free energy of formation (ΔfGÖ) of PCCZ congeners. The relations of these thermodynamic parameters with the number and position of Cl atom substitution (NPCS) were discussed, and it was found that there existed high correlation between thermodynamic parameters (entropy (SÖ), ΔfHÖ and ΔfGÖ) and NPCS. According to the relative magnitude of their ΔfGÖ, the relative stability order of PCCZ congeners was theoretically proposed. Moreover, using a statistical thermodynamics calculation program based on Gaussian 03 output files, the values of molar heat capacity at constant pressure (Cp,m) from 200 to 1800 K for the PCCZ congeners were calculated, and the temperature dependence relation of them was obtained using the least-squares method, which suggested that there be very good relationships between Cp,m and temperature (T, T－1 and T－2) for almost all the PCCZ congeners.

Key words: polychlorinated carbazoles, density functional theory (DFT), method of position of Cl atom substitution (NPCS), thermodynamic property, relative stability, molar heat capacity at constant pressure (Cp,m)