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Calculation of the nitrogen screening constants of some N ‐heterocycles
Author(s) -
Ebraheem K. A. K.,
Webb G. A.,
Witanowski M.
Publication year - 1978
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270110107
Subject(s) - cndo/2 , nitrogen , chemical shift , tautomer , chemistry , pyridine , pyrrole , computational chemistry , thermodynamics , stereochemistry , organic chemistry , molecule , physics
Absolute nitrogen screening constants and chemical shifts of some N ‐heterocycles are calculated within the CNDO/S level of approximation to Pople's model. Satisfactory agreement between calculated and observed nitrogen chemical shifts is obtained in most cases. The application of the results to the study of tautomeric equilibria is discussed. ‘Pyridine‐type’ nitrogen chemical shifts are dominated by n → π* transitions together with significant contributions from π → σ* and σ → π* transitions whereas the latter two are the dominant ones for ‘pyrrole‐type’ nitrogen nuclei.