Thermodynamic properties and relative stability of polybrominated phenoxathiins by density functional theory

Abstract

The thermodynamic properties of 135 polybrominated phenoxathiins (PBPTs) 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 standard enthalpy of formation (ΔfHO©) and standard free energy of formation (ΔfGO©) of PBPTs congeners. The relations of these thermodynamic parameters with the number and position of Br atom substitution (NPBS) were discussed, and it was found that there exist good correlations between thermodynamic parameters (entropy (SO©), ΔfHO© and ΔfGO©) and NPBS. According to the relative magnitude of their ΔfGO©, the order of relative stability of PBPT congeners was theoretically proposed. Moreover, using a statistical thermodynamics calculation program based on Gaussian output files, the values of molar heat capacity at constant pressure (Cp,m) from 200 to 1800 K for PBPT congeners were calculated, and the temperature dependence relation of them was obtained using the least-squares method. Key words: Polybrominated phenoxathiins, the number and position of Br atom substitution (NPBS), thermodynamic property, relative stability, molar heat capacity at constant pressure (Cp,m).