RESUMEN
Nitro substituted pyridyl sulfide and amine derivatives were found to exhibit many fragmentation mechanisms a behaviour which is due to the high reactivity of nitropyridyl, nitro heterocyclic and nitro aromatic compounds. The most common mechanism in nitropyridyl derivatives is the ring closure through expulsion of nitrous acid molecule either by elimination of hydrogen and nitro radicals in two steps or a concerted mechanisms. Moreover, the elimination of nitrous acid molecule may occure via skeletal rearrangement of the molecular ion followed by successive loss of hydride and nitroside radicals to form a cyclic fragment. These mechanisms showed the importance of ortho effect, which favours the elimination of HNO2 molecule from the molecular ion. These mechanisms of ring closure could be confirmed on the basis of studied fragmentation processes by tandem mass spectrometry. It is usually used to propose the fragmentations pathways by following up the mass spectra produced from each individual ion