Mesoionic 1.3-dimethyltetrazoles of the type A with sulfur, oxygen and nitrogen exocyclic groups, and related mono-and di-methylated tetrazoles have been investigated by means 'H, 13C, 14N and 15N N M R spectroscopy. The measurements were carried out in Me,SO and/or CF,CO,H solutions. The location of the protonation sites of the tetrazoles has been determined. The hydrogen atom is located on the exocyclic group of the mesoionic aminotetrazole 1, whereas the monomethylated and unsubstituted tetrazoles are protonated a t the N-4 position (compounds 4, 6, 8, 11-13). The monomethylated and non-ring substituted tetrazoles (compounds 4-8, 11-1 4 and 16) exist as nonmesoionic compounds, but compounds 1, 2, 9, I0 and 15 have a mesoionic structure.Mesoionic compounds attract attention due to interest in their atypical structures, pharmacological properties,' ring-chain taut omerism, protonation and applications in organic synthesis. '.' Previously, the structures of some mesoionic compounds were investigated by multinuclear NMR methods. It was shown that the 14N and "N NMR techniques were especially useful tools for studying the examples presented here for the class of compounds chosen. Thus, I5N NMR is applied to the investigation of structure and site of protonation of some five-membered Previously I3C, l4N, 15N and 1 7 0 NMR spectroscopy were used to study the mesoionic I-thia-2,3,4-triazoles. 1 -oxa-2,3,4-triazoles,' o,l ' type B mesoionic diazoles ' * and type B mesoionic 2,3-diphenyltetrazoles, 'where type A tetrazoles were disubstituted in positions 1 and 3 and type B ones were disubstituted in positions 2 and 3. However, type A mesoionic tetrazoles had not been investigated previously by multinuclear NMR methods. As a part of our ongoing study of mesoionic structures. we have chosen to examine some mesoionic 1,3-dimethyItetrazoles with various exocyclic groups, and related compounds.Puper 3 /0723 3 I
