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

The thermodynamic properties of 75 polyfluorinated dibenzo-p-dioxins (PFDDs) in the ideal gas state at 298.15K and 1.013 x 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 (Delta H-f degrees) and standard free energy of formation Delta G(f)degrees 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 degrees), Delta H-f degrees and Delta G(f)degrees) and N-PFS. According to the relative magnitude of their Delta G(f)degrees, the relative stability order of PFDD congeners was theoretically proposed. (C) 2010 Elsevier B.V. All rights reserved.