Theoretical study on hydrophilicity and thermodynamic properties of polyfluorinated dibenzofurans

Logarithm values of octanol-water partition coefficients (logK(ow)) of polyfluorinated dibenzofurans (PFDFs) were calculated based on group contributions, and their thermodynamic properties in the ideal gas state at 298.15 K and 1.013 × 10(5) Pa were calculated using a combination of quantum mechanical computations performed with the Gaussian 03 program at the B3LYP/6-311G(*) level. The isodesmic reactions were designed to calculate standard enthalpy of formation (ΔH(f)(θ)) and standard free energy of formation (ΔG(f)(θ)) of PFDF congeners. By establishing relationships between these properties (including logK(ow), standard state entropy S(θ), ΔH(f)(θ),ΔG(f)(θ)) and the number and position of fluorine atom substituents (N(PFS)), it was found that the fluorine substitution pattern strongly influences all of these properties of the compounds. The relation curve of logK(ow) values varying with the fluorine substitution pattern presented a three-level sawtooth shape. Intramolecular repulsive forces exist between an oxygen-adjacent fluorine atom on phenyl ring and the oxygen of dibenzofuran, between ortho-substituted fluorine atoms on a phenyl ring, and between two adjacent fluorine atoms on different phenyl rings. Their repulsion energies were ascertained by comparing ΔG(f)(θ) values to be approximately 14 kJ mol(-1)-17 kJ mol(-1), 18 kJ mol(-1)-22 kJ mol(-1) and 7 kJ mol(-1)-9 kJ mol(-1), respectively. According to the relative magnitude of their ΔG(f)(θ), the relative stability order of PFDF congeners was theoretically proposed.