Energy & Fuels, Vol.19, No.2, 508-511, 2005
Unambiguous resolution of alpha-methyl and alpha-methylene protons in H-1 NMR spectra of heavy petroleum fractions
In this paper, results of gradient selected (gs) NMR experiments for editing the H-1 NMR spectra of wide range of petroleum fractions are presented. Two such experiments have been performed which edit the proton spectra, with respect to carbon multiplicity: one results in the generation of selective CHn (n = 3, 2, 1) sub-spectra (1d-hmqc), and the other offers carbon-13 distortionless enhancement by polarization transfer (DEPT) type editing of the proton spectra (1d-hsqc). Both the experiments result in unambiguous resolution of alpha-methyl and a-methylene groups appearing in highly overlapped region from 2 ppm to 4.5 ppm, leading to better characterization of petroleum products. The proton editing experiments also provide the quantitative extent of overlap between various groups. The experiments are quite robust, simple to execute, and work well for the entire range of petroleum fractions.