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Carbon‐13proton coupling constants in N ‐substituted imidazoles. A 13 C NMR study and MO calculations
Author(s) -
Pachler K. G. R.,
Pachter R.,
Wessels P. L.
Publication year - 1981
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.1270170411
Subject(s) - imidazole , chemistry , ring (chemistry) , pyridine , pyrrole , coupling constant , proton , cationic polymerization , proton nmr , nitrogen , spectral line , medicinal chemistry , stereochemistry , organic chemistry , physics , particle physics , quantum mechanics , astronomy
The 13 C NMR data of imidazole, and N ‐methyl‐, N ‐acetyl‐, N ‐trifluoroacetyl‐, N ‐heptafluorobutyryl‐ and 2‐methyl‐imidazoles, were obtained from proton‐noise decoupled and single frequency NOE 13 C NMR spectra. The considerable changes in the directly‐bonded (C, H) coupling constants upon N ‐acetylation of the imidazole ring, which are comparable to those noted when going from the neutral to the cationic form of imidazole, are primarily due to the large π‐electron transfer ability of the N ‐acetyl‐ and N ‐trifluoroacetyl‐substituents. The differences in magnitude of the three‐bond (C, H) coupling constants along different paths in the imidazole ring may be attributed to the larger π‐contributions across a pyridine‐like nitrogen than along a pyrrole‐like nitrogen.