A MULTINUCLEAR NMR-STUDY OF SOME MESOIONIC 1,3-DIMETHYLTETRAZOLES, 1-METHYLTETRAZOLES AND 2-METHYLTETRAZOLES AND RELATED-COMPOUNDS

Mesoionic 1,3-dimethyltetrazoles of the type A with sulfur, oxygen and nitrogenexocyclic groups, and related mono- and di-methylated tetrazo les have been investigated by means H-1, C-13, N-14 and N-15 NMR spect roscopy. The measurements were carried out in Me2SO and/or CF3CO2H sol utions. The location of the protonation sites of the tetrazoles has be en determined. The hydrogen atom is located on the exocyclic group of the mesoionic aminotetrazole 1, whereas the monomethylated and unsubst ituted tetrazoles are protonated at the N-4 position (compounds 4, 6, 8, 11-13). The monomethylated and non-ring substituted tetrazoles (com pounds 4-8, 11-14 and 16) exist as non-mesoionic compounds, but compou nds 1, 2, 9, 10 and 15 have a mesoionic structure.