Theoretical study on hydrophilicity and thermodynamic properties of polyfluorinated dibenzofurans

Abstract

Logarithm values of octanol–water partition coefficients (log K 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 ( Δ H f θ ) and standard free energy of formation ( Δ G f θ ) of PFDF congeners. By establishing relationships between these properties (including log K ow, standard state entropy S θ, Δ H f θ , Δ G 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 log K 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 Δ G 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 Δ G f θ , the relative stability order of PFDF congeners was theoretically proposed.