Theoretical studies of the conformations and 19F NMR spectra of linear and a branched perfluorooctanesulfonamide (PFOSAmide)

Technical perfluorooctanesulfonate (PFOS) and its derivatives, such as perfluorooctanesulfonamide (PFOSA), are not clean compounds but, instead, complex mixtures of linear and branched isomers, and other compounds including sulfonate homologues. Questions have been raised as to whether the linear an...

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Bibliographic Details
Published in:Chemosphere (Oxford) 2007-10, Vol.69 (8), p.1213-1220
Main Authors: Liu, P., Goddard, J.D., Arsenault, G., Gu, J., McAlees, A., McCrindle, R., Robertson, V.
Format: Article
Language:English
Subjects:
Applied sciences
Computational modeling
Conformations
Exact sciences and technology
Fluorine - analysis
Fluorine NMR spectroscopy
Fluorocarbons - chemistry
Global environmental pollution
Isotopes
Magnetic Resonance Spectroscopy
Models, Chemical
Molecular Conformation
Perfluorooctanesulfonamide
PFOSA
Pollution
Sulfonamides - chemistry
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Summary:Technical perfluorooctanesulfonate (PFOS) and its derivatives, such as perfluorooctanesulfonamide (PFOSA), are not clean compounds but, instead, complex mixtures of linear and branched isomers, and other compounds including sulfonate homologues. Questions have been raised as to whether the linear and the branched isomers behave differently in the environment. However, little is known about the physical properties or the finer details of the structures of the individual branched isomers. This study sought an effective computational method to model the preferred conformations of PFOS derivatives, and the energy differences between them and to determine if these results can be used to explain the temperature dependence of their NMR spectra. Good predictions of the 19F chemical shifts were obtained for some PFOSA-type molecules with a computational approach [B3LYP-GIAO/6-31++G(d,p)//B3LYP/6-31G(d,p)] that is relatively inexpensive. Large 5 J FF couplings found in one of the branched isomers could be rationalized on the basis of the relevant F–F distances in the optimized structure. At low temperatures, the splitting observed in the NMR spectrum at C-1 for these sulfonamides can be explained by the existence of the two conformers predicted by the computations.
ISSN:0045-6535
1879-1298
DOI:10.1016/j.chemosphere.2007.06.006