Studies of thermodynamic properties and relative stability of a series of polyfluorinated dibenzo- p-dioxins by density functional theory

Abstract

The thermodynamic properties of 75 polyfluorinated dibenzo- p-dioxins (PFDDs) in the ideal gas state at 298.15 K and 1.013 × 10 5 Pa have been calculated at the B3LYP/6-311G* level using Gaussian 03 program. The isodesmic reactions were designed to calculate standard enthalpy of formation (Δ H f°) and standard free energy of formation (Δ G f°) of PFDDs congeners. The relations of these thermodynamic parameters with the number and position of fluorine atom substitution ( N PFS) were discussed, and it was found that there exist high correlations between thermodynamic parameters (entropy ( S°), Δ H f° and Δ G f°) and N PFS. According to the relative magnitude of their Δ G f°, the relative stability order of PFDD congeners was theoretically proposed.