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The study of 29Si MAS NMR spectra of zeolites of both low and high Si/Al ratios has provided insight on the factors affecting the residual 29Si line-widths of these materials. It is found that the residual linebroadening in low Si/Al ratio zeolites is due to the distribution of local environments of a particular Si(nAl) type, resulting from the distribution of aluminium atoms in second and further coordination spheres. This is complicated in some cases by a distribution of chemical shifts resulting from crystallographic inequivalence, each of which is subject to the above environmental broadening factors.

Carbon-13 chemical shifts are reported for a series of carcinogenically active and related inactive polynuclear hydrocarbons. Resonance assignments for complex systems such as 3-methylcholanthrene, dibenzanthracenes, benz[a]anthracene and its 7-methyl and 7,12-dimethyl derivative, have been made primarily from a study of simpler models, including phenanthrene, triphenylene, and anthracene. Selective proton decoupling has been employed extensively. Quaternary carbon assignments have been aided by deuterium isotope shift and spin–lattice relaxation time measurements. Vicinal C—D couplings have been found to be unreliable as means of assignment for quaternary carbons.

The hydrocarbon-type content of petroleum fractions has tradltlonally been determlned by uslng different techniques but often wlth poor agretsment among the varlous results for a glven sample. In thls study, three different fractlons were analyzed by using mass spectrometric (MS), nuclear magnetlc resonance (NMR), and fluorescent Indicator analysis (FIA) techniques. The lac and 'H NMR results were flrst converted from an atomic to a molecular bask. The MS, NMR, FIA, and bromllne number results are compared, wlth special attention given to the olefinlc contents. The assumptlons Involved In, and lirnltations of, each technlque are Identified. The analysis of llght fractions free of dlenes, olefins, and heteroatom-ccontalning species is best performed by MS methods. The atomic hydrogen and carbon dlstrlbutlon from the NMR method Is found to be applicable to all samples examined. Whlle these atomic data can be correlated with the properties of the fractlons, the NMR resuns on a molecular basis are uncertain because of the number of assumptions Involved.Performance characteristics and other properties of petroleum products depend on their chemical compositions. Among the determining factors is the content of aromatic, olefinic, and saturated hydrocarbons. For example, the amounts of aromatic and saturated hydrocarbon affect the combustion properties of fuels, while olefins have a marked effect on a fuel's stability.Petroleum fractions must be subjected to various refining treatments to meet final product specifications. Such treatments always lead to a change in the constituent hydrocarbons. A rapid method of determining the proportions of the hydrocarbons would be a valuable tool for controlling technological parameters during production.Mass spectrometric (MS) techniques have been extensively applied, for many years to various types of hydrocarbon analysis, and new developments have been periodically reviewed (1). A number of MS analytical methods were standardized (2). ThLese can be applied with good precision to samples which fall within the limitations of the methods. Two important limitations are that there be very low amounts of olefins and of heteroatom (i.e., S-, N-, 0-) containing compounds. Both these classes of compounds are a source of interference in the calculations based on the spectral information. It appears,, therefore, that MS methods are suitable only for analyzing refined products from which these interferences are usually absent.Nuclear magnetic resonance spectrometry (NMR) is a powerful tool in fuel analysis as well (3). Preferential use of this technique in analysis of coal-derived liquids, i.e., liquids with high content of heteroatoms, suggests that the interference of the latter i8 less critical. An additional advantage of NMR over MS is NMR's ability to analyze nonvolatile samples, including semisolids and solids.The gas chromatographic-mass spectrometric (GC/MS) technique acts at a molecular level; that is, there is a molecular separation followed by detection and analysis of molecules. T...