Nuclear magnetic resonance hydrogen distribution

One has seen that the number of individual components in a hydrocarbon cut increases rapidly with its boiling point. It is thereby out of the question to resolve such a cut to its individual components instead of the analysis by family given by mass spectrometry, one may prefer a distribution by type of carbon. This can be done by infrared absorption spectrometry which also has other applications in the petroleum industry. Another distribution is possible which describes a cut in tei ns of a set of structural patterns using nuclear magnetic resonance of hydrogen (or carbon) this can thus describe the average molecule in the fraction under study. 

Nuclear magnetic resonance spectroscopy has proved to be of great value in fossil fuel research because it allows rapid and nondestructive determination of the total hydrogen content and distribution of hydrogen among the chemical functional groups present (Bartle and Jones, 1978 Retcofsky and Link, 1978 Petrakis and Edelheit, 1979 Snape et al., 1979 Davidson, 1980, 1986 Miknis, 1982, 1988 Calkins and Spackman, 1986 Cookson and Smith, 1987 Bartle,... 

The inhomogeneity of the structure is completely missed in the X-ray RDF measurements, but can be observed by small angle X-ray or neutron diffraction, and also by nuclear magnetic resonance (NMR) measurements of the hydrogen distribution, described in Section 2.3.2. 

Nuclear magnetic resonance spectroscopy has also been used to derive structural parameters for the distribution of aliphatic hydrogen in coal and its extraction products. A ratio of four methylene groups per methyl group was noted also, the methyl group content was higher in the soluble material and varied with the solvent power of the solvent. 

Nuclear magnetic resonance (NMR), to establish distribution of hydrogen and carbon [215,216] and NMR with H/ C [217] to provide average structure. 

Stereochemical studies based on C-nuclear magnetic resonance spectroscopy ( C-NMR) showed the presence of eight cis and trans allylic hydroperoxides (Table 2.1). To determine the isomeric distribution of allylic hydroxyooctadecenoate derivatives, cis and trans fractions were separated by silver nitrate-thin layer chromatography (TLC), a procedure that separates according to the number, position and geometry of double bonds, and they were hydrogenated prior to GC-MS analyses of the TMS ether derivatives. More recently, the six major hydroperoxide isomers of methyl oleate were partially separated by silica HPLC, and identified by chemical-ionization mass spectrometry and IH NMR (Table 2.1). These hydroperoxide isomers were better separated as the hydroxy octadecenoate derivatives by the same silica HPLC method and re-analysed by GC-MS. 

---