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Proton‐coupled 13 C NMR and { 14 N}— 1 H‐INDOR of highly‐substituted 6‐membered heterocycles. I—trisubstituted pyridones and isomeric aminopyrones; tetrasubstituted pyridines
Author(s) -
Cavagna F.,
Pietsch H.
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.1270110407
Subject(s) - geminal , chemical shift , chemistry , electronegativity , substituent , coupling constant , amide , proton , nuclear magnetic resonance spectroscopy , spectral line , crystallography , computational chemistry , stereochemistry , organic chemistry , physics , astronomy , particle physics , quantum mechanics
Abstract The structural elucidation by NMR spectroscopy of trisubstituted α‐pyridones and the isomeric 2‐amino‐γ‐pyrones as well as their internal and external pyrylium salts is described. The most useful parameter for the differentiation between α‐pyridones and isomeric γ‐pyrones is the geminal coupling constant 2 J (C‐6, H‐5) which changes from ∼2.5 Hz to ∼7 Hz whenever the cyclic amide group is replaced by an oxa‐function; this applies to both the γ‐pyrones and their pyrylium salts. The value of J (C‐6, H‐5) in the pyridones resembles that of the analogous coupling in N ‐vinylacetamide, whose sign determination by the selective population inversion (SPI) technique is reported. The 13 C chemical shifts of seven pyridones, pyrones and pyrylium salts are reported and their structural correlations are discussed. Quick structural assignments in these classes of compounds may also be performed by evaluating the 14 N chemical shifts, which often are accessible by the { 14 N}— 1 H‐INDOR technique. The proton coupled 13 C NMR spectra of two tetrasubstituted pyridines are also reported, and empirical correlations between long range CH coupling constants and substituent electronegativity are discussed.