Theoretical Studies of the Conformations and super(19)F NMR Spectra of Linear and a Branched Perfluorooctanesulfonamide (PFOSAmide)

The best practical computational method for modeling the preferred conformations of perfluorooctanesulfonate (PFOS) derivatives and the energy differences between them were evaluated. The free induction decays were processed using exponential multiplication before Fourier transformation. The testing demonstrated that the calculated chemical shifts were sensitive to the choices of basis set for both the geometry optimizations and the gauge independent atomic orbital (GIAO) calculations. The density functional calculations were more accurate than Hartree-Fock for most basis sets. At low temperatures, the splitting observed in the NMR spectrum at C-1 could be explained by the existence of the two conformers predicted by calculations.