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Изучение структурных параметров и кислотно-основных свойств тиобарбитуровой кислоты А. П. Лакеев, Н. М. Коротченко, Э. Р. Сайфулин

By: Лакеев, Александр ПавловичContributor(s): Коротченко, Наталья Михайловна | Сайфулин, Эдуард РияловичMaterial type: ArticleArticleContent type: Текст Media type: электронный Other title: Examination of structural parameters and acid-base properties of thiobarbituric acid [Parallel title]Subject(s): тиобарбитуровая кислота | кислотно-основные равновесия | лиганд | pH-метрия | УФ-спектрофотометрия | ИК-спектроскопия | квантово-химические расчетыGenre/Form: статьи в журналах Online resources: Click here to access online In: Журнал Сибирского федерального университета. Химия Т. 12, № 1. С. 6-17Abstract: The stepwise proton-ligand stability constant of thiobarbituric acid (TBA) singly charged anion was determined in an aqueous solution via pH-metry and UV-spectrophotometry at ionic strength I = 0.1 (NaCl) and temperature T = 20 °C (25 °C). The values (lg æ2) obtained by these methods show satisfactory convergence, namely, 2.30 ± 0.01 (20 °C), 2.16 ± 0.01 (25 °C) and 2.37 ± 0.06 (20 °C), respectively. Additionally, the UV-spectrophotometry results have shown that TBA could exist in the two conjugate forms within pH of 1.1–9.2. Quantum chemical calculations have confirmed that the keto-form is more thermodynamically stable than the enol one. The obtained values for geometric parameters and for the effective charges on Mulliken atoms make it possible to describe the structure of this tautomer and to argue that the acid mainly functions as an N- and/or O-donor ligand during the complexation with metal ions. IR-spectroscopy data have confirmed that the investigated solid thiobarbituric acid has represented mainly by ketone tautomer.
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The stepwise proton-ligand stability constant of thiobarbituric acid (TBA) singly charged anion was determined in an aqueous solution via pH-metry and UV-spectrophotometry at ionic strength I = 0.1 (NaCl) and temperature T = 20 °C (25 °C). The values (lg æ2) obtained by these methods show satisfactory convergence, namely, 2.30 ± 0.01 (20 °C), 2.16 ± 0.01 (25 °C) and 2.37 ± 0.06 (20 °C), respectively. Additionally, the UV-spectrophotometry results have shown that TBA could exist in the two conjugate forms within pH of 1.1–9.2. Quantum chemical calculations have confirmed that the keto-form is more thermodynamically stable than the enol one. The obtained values for geometric parameters and for the effective charges on Mulliken atoms make it possible to describe the structure of this tautomer and to argue that the acid mainly functions as an N- and/or O-donor ligand during the complexation with metal ions. IR-spectroscopy data have confirmed that the investigated solid thiobarbituric acid has represented mainly by ketone tautomer.

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