Nitromethane, mass spectra

In addition to short-lived molecules that were assigned to the structure classes discussed above, there are various interesting intermediates that are mentioned here separately. Nitrosomethane (38), which is the less stable tautomer of formaldoxime, was generated by collisional reduction of the stable cation-radical and characterized by NRMS [155,156]. The precursor cation for 38 was produced by three different reactions, e.g., elimination of OH upon exothermic protonation of nitromethane [156], electron-induced loss of O from nitromethane [155, 156], and electron-induced CH20 extrusion from ethyl nitrite [156] (Scheme 15). Nitrosomethane gives rise to a moderately abundant survivor ion in the +NR+ mass spectrum and does not undergo unimolecular isomerization to any of its more stable tautomers. 

On photolysis, nitromethane yielded NO2 and methyl (Bielski and Timmons, 1964) as in its mass spectrum and, unlike aromatic nitro compounds, showed no significant loss of NO (Aplin et al., 1965). The mass spectra of many aromatic nitro compounds show evidence for... 

The ions observed as a result of unimolecular dissociations (metastable ions) in the mass spectrometer correspond to reactions in the low- Xs time frame ". Due to the duality of the reaction rate and the available energy, only processes with rather low-energy requirements are observed ", which is nicely reflected in the metastable ion spectrum of nitromethane (Figure 1) . Two dominant processes, i.e. the loss of OH (m/z 44) and CH3O (m/z 30), respectively, are observed leading directly to the conclusion that these reactions have critical energies within a few hundredths of meV. Recent literature reviews offer excellent discussions on the metastable ion dissociations. Nevertheless, it appears reasonable to summarize the more important aspects. 

---