Investigation of Solvent and Concentration Effects on the Tautomeric Equilibrium of Acetamide
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Date
2020-03-06
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Addis Ababa University
Abstract
Solvent effects on tautomeric equilibria of acetamide have been investigated by Infra-red spectroscopic technique. IR absorption spectra of solvents of varying polarity were recorded at different concentrations. The solvents used were chosen to cover wide polarity ranges that include cyclohexane, 2-propanol, methanol and acetonitrile. Increasing the solvent polarity, a shift in absorption maxima to lower frequency (bathochromic shift) was observed. Dilution studies on acetamide showed that the relative intensity of the bands with respect to the main antisymmetric stretching bands were concentration dependent which was attributed to intermolecular association (aggregation).From the results obtained, when the acetamide concentration was diluted, the third band disappeared and the second band decreased steadily. This indicated that the carbonyl absorption band in acetamide was concentration dependent. Further, as the concentration was decreased, the relative intensity of the bands gradually decreased. The presence of a concentration dependent second band (band IΙ) was a clear sign of intermolecular aggregation resulted in dimer that is favored when the amount of acetamide molecule in the medium was higher. As expected, the aggregation of acetamide molecule was higher in non-polar solvents. The presence of isosbestic point in cyclohexane indicated the monomer dimer coexisted in equilibrium. The relative stability of amide-imidol tautomeric equilibrium has been studied over a wide range of solvent polarity. In polar solvents the tautomeric equilibrium shifted towards amide tautomer and in non-polar solvents the tautomeric equilibrium shifted in favor of the imidol tautomer due to formation of self-association.
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Solvent and Concentration Effects, Dimerization, Tautomerism, Acetamide, Ft-Ir