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1H, 13C and 15N NMR and IR studies of halogen-substituted tetrazolo[1,5-a]pyridines

✍ Scribed by P. Cmoch; H. Korczak; L. Stefaniak; G. A. Webb

Publisher: John Wiley and Sons
Year: 1999
Tongue: English
Weight: 85 KB
Volume: 12
Category: Article
ISSN: 0894-3230
DOI: 10.1002/(sici)1099-1395(199906)12:6<470::aid-poc151>3.0.co;2-u

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✦ Synopsis

The tetrazole-azide tautomerization of some halogen-substituted tetrazolo [1,5-a]pyridines was examined by IR spectroscopy at ambient temperature and by 1 H, 13 C and 15 N NMR spectroscopy at various temperatures. The tetrazolopyridines can exhibit equilibrium between the azide and the tetrazole forms. For some of them slow exchange occurs on the NMR time-scale, such that it is possible to estimate equilibrium constants. The position and nature of the substituent in the pyridine ring result in stabilization or destabilization of the tetrazole form and exert a strong influence on the values found for the equilibrium constants. A saturation transfer experiment was carried out for 5-bromotetrazolo[1,5-a]pyridine and the rate constants were estimated. Moreover, based on the van't Hoff equation, the enthalpy DH°and entropy DS°for the tautomerization were calculated. Ab initio calculated energies and charge distribution are in good agreement with differences observed in the tetrazole-azide equilibrium constants.

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