A multinuclear NMR study of some mesoionic 1,3-dimethyltetrazoles, 1- and 2-methyltetrazoles and related compounds

Abstract

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 ¹H, ¹³C, ¹⁴N and ¹⁵N NMR spectroscopy. The measurements were carried out in Me₂SO and/or CF₃CO₂H 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 at the N-4 position (compounds 4,6, 8, 11–13). The monomethylated and non-ring substituted tetrazoles (compounds 4–8, 11–14 and 16) exist as non-mesoionic compounds, but compounds 1, 2, 9, 10 and 15 have a mesoionic structure.