The tetrazole-azide tautomerism of some nitrotetrazolo [1,5-a]pyridines studied by NMR, IR spectroscopy and molecular orbital calculations

The 6-nitro- and 8-nitro- groups in the tetrazolo[1,5-a]pyridine molecule e xhibit completely different influences on the tetrazole-azide equilibrium. Introduction of the methyl-, nitro-, azido groups or a bromine atom in posi tions 5, 6, 7 or 8 of the nitrotetrazolopyridine produce changes in the equ ilibrium constants. Based on the IR spectra taken in the solid state, the t etrazole structure was assigned for almost all the compounds studied. Only one of them, 2,6-diazido-3-nitropyridine, exists in the diazido-form in the solid. The H-1, C-13, N-15, and O-17 NMR spectral parameters (coupling con stants, chemical shifts) as well as ab initio molecular orbital calculation s were used to describe the tetrazole-azide tautomerism in solutions. The d ifferences in the NMR parameters between the neutral compound (6,8-dinitrot etrazolo[1,5-a]pyridine) and its sigma-adducts are also included as data fo r distinguishing between both molecules. (C) 1999 Elsevier Science B.V. All rights reserved.