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1 H, 13 C and 15 N NMR and IR studies of halogen‐substituted tetrazolo[1,5‐ a ]pyridines
Author(s) -
Cmoch P.,
Korczak H.,
Stefaniak L.,
Webb G. A.
Publication year - 1999
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199906)12:6<470::aid-poc151>3.0.co;2-u
Subject(s) - chemistry , tautomer , tetrazole , azide , halogen , equilibrium constant , enthalpy , pyridine , computational chemistry , medicinal chemistry , thermodynamics , stereochemistry , organic chemistry , alkyl , physics
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 Δ H ° and entropy Δ S ° 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. Copyright © 1999 John Wiley & Sons, Ltd.