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Bifurcated hydrogen‐bonding effect on the shielding and coupling constants in trifluoroacetyl pyrroles as studied by 1 H, 13 C and 15 N NMR spectroscopy and DFT calculations
Author(s) -
Afonin Andrei V.,
Ushakov Igor A.,
Mikhaleva Al'bina I.,
Trofimov Boris A.
Publication year - 2007
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1949
Subject(s) - chemistry , intramolecular force , hydrogen bond , proton , pyridine , coupling constant , crystallography , ring (chemistry) , pyrrole , covalent bond , nuclear magnetic resonance spectroscopy , proton nmr , computational chemistry , stereochemistry , molecule , medicinal chemistry , organic chemistry , physics , particle physics , quantum mechanics
According to the 1 H, 13 C and 15 N NMR spectroscopic data and DFT calculations, bifurcated NH···N and NH···O intramolecular hydrogen bond is shown to be present in 2‐trifluoroacetyl‐5‐(2′‐pyridyl)‐pyrrole. This bifurcated hydrogen bond causes an increase in the absolute size of the 1 J (N,H) coupling constant by about 6 Hz, and the deshielding of the bridge proton by 2 ppm. DFT calculations show that the influence of the NH···N and NH···O intramolecular hydrogen bonds on the 1 J (N,H) coupling and proton shielding is almost additive, although the components of the bifurcated hydrogen bond slightly weaken each other. In 2‐trifluoroacetyl‐5‐(2′‐pyridyl)‐pyrrole, the coupling constants involving the fluorine and the NH covalent bond nuclei depend dramatically on the spatial position of the pyridine ring. The pyridine ring rotation operates as a quantum switch controlling the spin information transfer between the 19 F and 15 N nuclei, as well as the proton. Copyright © 2007 John Wiley & Sons, Ltd.