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The tautomerism of nitraminopyridines
Author(s) -
Gawinecki Ryszard,
Kolehmainen Erkki,
Rasała Danuta,
Suontamo Reijo
Publication year - 1995
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/poc.610081007
Subject(s) - tautomer , chemistry , chemical shift , hydrogen atom , ring (chemistry) , hydrogen , nitrogen , hydrogen bond , nuclear magnetic resonance spectroscopy , nitrogen atom , carbon 13 nmr , computational chemistry , stereochemistry , molecule , organic chemistry , group (periodic table)
1 H, 13 C and 15 N NMR data for nitraminopyridines are discussed in terms of tautomeric equilibria in these compounds. The favoured tautomer is determined mainly from 15 N NMR spectroscopy. The chemical shift of the nitrogen atom of the nitro group in nitraminopyridines and N ‐nitroanilines which cannot tautomerize vary from 28·0 to 35·4 ppm in DMSO solution. 3‐Nitraminopyridine and 2‐nitramino‐3‐ and ‐5‐nitropyridines behave similarly. In the 15 N NMR spectra of nitrimino‐1‐methyldihydropyridines, used as models, an upfield shift of that atom, different from that observed for 2‐nitraminopyridine, indicates the significance of the nitrimino tautomer. In contrast, a downfield shift of the ring nitrogen atom of some other compounds shows an increased weight of the nitramino tautomer. 3‐Nitraminopyridine, when dissolved in DMSO, does not have the zwitterionic structure. Changes in the chemical shift of the amino nitrogen atom are not readily interpreted. Some proton and carbon chemical shifts and hydrogen–hydrogen and carbon–hydrogen spin–spin coupling constants can also be used to determine the predominant tautomer of 2‐ and 4‐nitraminopyridines.