Aromatic hydrocarbon ions mass spectra

Figure 1.22c shows the LD/EI/FT/ICR mass spectrum of a second phosphite additive, WESTON 618 diphosphite. Although the molecular ion miz 732) is readily observed, its abundance is lower than for Ultranox 626 diphosphite or XF 2502, presumably because WESTON 618 diphosphite has saturated hydrocarbon chains in place of aromatic rings and therefore fragments more easily. Similar behaviour has been reported for other phosphate additives [43]. 

The mass spectra of most aromatic hydrocarbons show an intense molecular ion peak. The mass spectrum of toluene (Figure 14.14), for example, shows a large molecular ion peak at m/z 92. 

Example The EC mass spectrum of benzo[a]pyrene, C20H12, shows the negative molecular ion exclusively at m/z 252 (Fig. 7.14). This spectrum is representative for EC spectra of polycyclic aromatic hydrocarbons (PAHs) [87,88]. One particular PAH, fluoranthene, has recently received much attention as its ion serves as electron donating reactant ion in electron transfer dissociation (ETD, Chap. 9.15). 

Mass spectral data have frequently been used in the structural determination of boron heterocycles. One paper has been devoted to the mass spectra of some six-membered boron-nitrogen systems. It was concluded that the spectra could be interpreted analogously to their hydrocarbon counterparts. In all cases the molecular peak was the base peak of the spectrum (68T6755). Doubly charged molecular ions, a feature typical of aromatic compounds, are often encountered. It should be noted, however, that some certainly non-aromatic aminoboranes give such doubly charged ions as well. 

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