The behaviour in electrospray conditions of a series of thiazol-benzimidazolones and 2-benzimidazolylsulphanyl ethanones has been studied by means of multiple tandem mass spectrometry experiments. Even though the experimental conditions were the same, different behaviour is observed for the two classes of compounds. In the case of thiazol-benzimidazolones, the formation of a protonated complex with CH3OH employed as solvent is observed, but in the case of 2-benzimidazolylsulphanyl ethanones the formation of MNa+ ions is privileged. This behaviour has been related to molecular structure. The collisionally-induced decompositions of MH+ ions have been rationalised in terms of the Stevenson–Audier and even-electron rules, as well as on the basis of proton affinity data. Thus, protonated thiazol-benzimidazolones undergo facile loss of CO and a series of different decomposition pathways involving cleavage of the thiazolone ring that reflect the structure of the neutral fragments. In contrast, the decompositions of the protonated 2-benzimidazolylsulphanyl ethanones are mainly related to the piperazine moiety, suggesting that the protonation takes place on this substructural unit.
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