Mass spectral fragmentation pathways in some dinitroaromatic compounds studied by collision‐induced dissociation and tandem mass spectrometry

A collision‐induced dissociation study of a series of dinitroaromatic compounds was carried out using a tandem BB mass spectrometer. Fragmentation pathways were determined in the electron impact mode. Loss of NO2˙ from the molecular ion was observed In most of the investigated compounds. In some compounds loss of NO2˙ occurred only after loss of OH˙. In other compounds it was not observed at all because of competitive processes, such as loss of NO˙, CO2, CH2O, C2H4 or H2O. Loss of NO˙ was a major decomposition pathway, forming ‘dished peaks’ in some of the compounds having a nitro group ortho to a phenyl group, indicating a release of kinetic energy associated with the decomposition. Loss of OH˙ due to an ‘ortho effect’ occurred in compounds where a nitro group was ortho to a group containing a labile hydrogen, but was not observed when competitive processes such as loss of NO˙, NO2˙ or H2O occurred. ‘Nitro to nitrite’ isomerization was suggested to explain the decarboxylation process in 2,4‐ and 2,5‐dinitrobenzoic acid and the loss of COH2 in 2,4‐dinitroanisole.