Studies in organic mass spectrometry—V: N-arylsulphonyliminopyridinium betaines

The mass spectral fragmentation of N-arylsulphonyliminopyridinium betaines has been rationalized using high resolution mass spectrometry as well as deuterium labelling. The most characteristic features are a very facile N S bond cleavage and skeletal rearrangements accompanied by the expulsion of SO₂ from the molecular ion and the [M 1] ion to the corresponding ionized N-aryliminopyridinium betaines and azacarbazoles, respectively. The presence of methyl substituents at the α-position of the pyridine ring has a significant effect on the mode of the fragmentation.