| Resumo: |
The gas and solution phase relative thermodynamic stabilities of the 89 perfluorooctane sulfonic acid (PFOS) congeners play an important role in assessing whether synthetic conditions for commercial mixtures are under thermodynamic or kinetic control, and in calculating various physico-chemical properties for these important industrial compounds and environmental contaminants. In the present study, 4,272 gas and solvent phase (water and n-octanol) calculations were conducted at various levels of semiempirical (PM6), density functional (B3LYP, B97D, PBE1PBE [PBE0], and M062X functionals with the 6-311++G(d,p) basis set), and second order Moller-Plesset perturbation (MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p)) theory and the SMD, IEFPCM-UFF, and CPCM implicit solvation models on the 89 PFOS congeners in both their acid and anionic forms. The B3LYP functional consistently and incorrectly predicts substantially increasing thermodynamic stability of PFOS isomers with increasing linearity of the perfluoroalkyl chains. By comparison, PM6, M062X, and MP2 calculations more closely reflect the expected patterns of thermodynamic stability for branched versus linear PFOS congeners.
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