Simplification and assignment of proton and two-dimensional hetero-correlated NMR spectra of petroleum fractions using gradient selected editing pulse sequences

In this paper, gradient selected (gs) NMR experiments are presented for editing the proton, and two-dimensional (2D) 1H–13C-correlation spectra of different fractions of the petroleum according to the carbon multiplicity. The state of the art experiments allow the much sought after simplification and resolution of the proton, and 2D 1H–13C correlated NMR spectra of such fractions in considerably reduced acquisition times. The proton-edited experiments offer a new and much convenient way of unambiguous estimation of cut-off points between signals from α-methyl and α-methylene protons in 1H NMR spectra of petroleum fractions. The gs edited 2D 1H–13C correlated spectra of the fractions provide carbon multiplicity information and hetero-nuclear correlation with improved sensitivity in a single experiment leading to complete spectral assignment. These experiments have been applied to complex petroleum fractions for the first time, and show lot of potential to resolve various hitherto unanswered issues concerning the interpretation of the complex NMR spectra of the petroleum products.