Influence of the substituent on the major decomposition channels of the NO2 group in para-substituted nitrobenzenes: a tandem mass spectrometric study

The relative extents of loss of NO2 and NO were determined by 70 eV electro n ionization and tandem mass spectrometry using B/E linked scans to investi gate metastable (unimolecular) and collision-induced dissociation processes for molecular ions formed by electron ionization of para-substituted nitro benzene compounds. The substituents used (NO2, CHO, H, OCH3) represent a wi de range of electron donor-acceptor properties. Loss of NO2 was favored by electron-withdrawing groups, while an electron-donor group favored loss of NO. Ion fragmentation mechanisms are consistent with the hypothesis that NO 2 to ONO (nitro to nitrite) isomerization precedes the loss of NO. Ring fra gmentation (loss of CO) was observed only after all of the electron-withdra wing groups had dissociated. while the electron-donor group OCH3 remained a ttached to the ring in the analogous CO elimination. These results are plac ed in the context of the thermolysis behavior of nitroaromatic explosives. Copyright (C) 1999 John Wiley & Sons, Ltd.