Dynamic Variable Temperature NMR Investigation of Tautomerism in Nicotinamide
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Date
2024-08
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Addis Ababa University
Abstract
Dynamic Variable temperature proton nuclear magnetic resonance (1H NMR) spectrometry has been used to study variable temperature nicotinamides. A functional group with limited rotation around the C-N bond, the dynamic nicotinamide bond is studied using variable temperature (VT) 1H NMR spectroscopy.
The majority of the structural and stereochemical characteristics of an organic compound can be revealed by 1H NMR spectroscopy, which is categorized under the category of 1H NMR spectroscopy or proton magnetic resonance (PMR) spectroscopy in conjunction with 13C NMR. A compound's potential carbon atom composition and number of non-equivalent carbon atoms can both be ascertained from its 13C-NMR spectra. As a result, 13C-NMR offers precise information about a molecule's carbon skeleton.
The amide molecule in the studies exhibited two separate peaks, each of which corresponded to the amine group. The peak separation decreased with increasing temperature, suggesting the presence of a rotating barrier around the amide bond.
At 328 K, the two peaks were seen to combine. Acetonitrile and chloroform, two generally nonpolar solvents, cause amide and related compounds to undergo substantial temperature-dependent structural changes, according to variable-temperature 1H NMR investigations.
The behavior that has been seen indicates that the rotational barrier about the C=N bond cannot be the cause of the peak splitting. Instead, it implies that a tautomeric equilibrium is the cause of the two peaks, which come from two distinct chromophores (O-H and =N-H chromophores).
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Keywords
1H NMR, Amide, Tautomeric Equilibrium, Variable Temperature, Rate 13C NMR