Abstract Fully optimized calculation and frequency analysis of 209 polybrominated diphenylamine (PBDPAs) compounds were carried out by using DFT method at the B3LYP/6-31G* level and their thermodynamic parameters in the ideal gas state at 298.15 K and 101.3 kPa were obtained. The isodesmic reactions were designed to calculate standard enthalpy of formation (ΔfH?) and standard free energy of formation (ΔfG?) of PBDPAs congeners. The relationships of these thermodynamic parameters with the number and the position of Br atom substitution (NPBS) were established, it was found that there exists high correlation between entropy (S?), standard enthalpy of formation (ΔfH?), standard free energy of formation (ΔfG?) and NPBS (R2≥0.984). The stability of PBDPAs congeners was theoretically proposed based on the relative magnitude of their ΔfG?. The values of Cp,m were calculated by using statistical thermodynamics calculation Program at the temperatures between(200 to 1000)K based on Gaussian 03 output files, and obtained relative equation between Cp,m and temperature by the least square method, found that Cp,m and T、T-1、T-2 have a very good relationship(R2=1.000). The isomer which has the highest toxicity may be has three numbers of Br atom according the Vm of PBDPAs.

Key words: polybrominated diphenylamine, density functional theory (DFT), method of position of Br atom substitution, thermodynamic property, relative stability