Chemistry

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Browsing Chemistry by Subject "1H NMR"

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    Dynamic Variable Temperature NMR Investigation of Tautomerism in Nicotinamide
    (Addis Ababa University, 2024-08) Dejene Girma; Mesfin Redi
    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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    Investigation of Rotational Barrier in Nicotinamide and Picolinamide Using Temperature-Dependent 1H NMrR Spectra
    (Addis Ababa University, 2018-05-05) Mohammed, Ali; Redi, Mesfin (PhD); Tsegazab, Yisak (Mr)
    Rotational barrier in nicotinamide and picolinamide have been investigated employing temperature-dependent proton nuclear magnetic resonance (1H NMR) spectrometry. In nicotinamide and picolinamide the two protons on the nitrogen appeared at different chemical shift positions revealing that they are magnetically non-equivalent. In the experiments, nicotinamide showed two distinct peaks corresponding to the amine group of the amide molecule, and the peak separation decreased as a function of temperature indicating a rotational barrier about the amide bond. The coalescence of the two peaks was observed at 328 K. Using through line shape analysis of the temperature dependent spectra; a rotational barrier of 17.9 kcal mol −1was calculated. Interestingly the opposite temperature dependence of the peak separation was observed in picolinamide in which the separation increased as the temperature was increased and no convergence was observed in the temperature ranges the experiments were conducted. The observed behaviour clearly demonstrates that the splitting of the peaks cannot be attributed to the rotational barrier about the C−N bond rather it suggests that the two peaks originate from two different chromophores (O−H and =N−H chromophores) resulting from a tautomeric equilibrium.