Electronic spectra sulfur compounds

The quantum mechanical interpretations of the electronic spectrum of I are not at aU satisfactory. This is partly due to the fact that there are no analogous compounds around to adjust the heteroatom parameters and there are more parameters to vary (model D) than observable ones. An improved all valence treatment for sulfur compounds is desirable. 

As these phenyl-anologs of isobutane all have a single tertiary hydrogen atom, they may be considered as possible precursors of tertiary carbonium ions. Phenyl derivatives were selected because phenyl groups are known to stabilize carbonium ions and independent existence of these ions have been amply demonstrated by cryoscopic measurements of sulfuric acid solutions of the corresponding carbinols (87, 88) and by conductivity measurements in liquid sulfur dioxide solutions of the corresponding halides and perchlorates (89, 90, 91). Also, the electronic spectra of these ions have been well characterized (92-96). Isobutane is not included in this list since only indirect evidence is available for the independent existence of the tertiary-butyl ion and its electronic spectrum is still in doubt. Studies involving this compound and other aliphatic hydrocarbons will be discussed separately in Section VI, C, 2, c. 

Despite the overall similarity between the XANES spectrum of the mixed model compounds and the asphaltene and coal samples, there are some significant differences in the relative energies of the various features. One possible explanation for these differences is that subtle electronic differences at the sulfur are reflected in the sulfur XANES. Such differences might be expected to arise from extended ring structures or from substituents. This will be a subject for further study. 

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