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Computational Study of the Acidity of Some Substituted Pyridinium Cations

The aim of this work was to investigate the acidity of the pyridinium cations using high-level quantum-chemical calculations, and to compare the calculated results to the existing experimental ones. The study included the full optimization and vibrational analysis of all of the conformers of keto and enol forms of 1?6 and all of the conformers of all corresponding deprotonated forms, both in vacuum and water, at B3LYP/6- 311+G(d, p) level of theory. The pKa values were calculated within the framework of a continuum solvation model, using IEF-PCM method. The computational results show that the keto?enol equilibrium is always shifted towards the keto form. Calculated pKa values are in a good agreement with the corresponding experimental values. Based on obtained results it is possible to analyze the influence of structure changes to the studied compounds acidity.

quantum-chemical calculations; acidity; pyridinium cations

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