An LFER study of the protolytic equilibria of 4-aryl-2,4-dioxobutanoic acids in aqueous solutions
| Autor: | Verbić Tatjana Ž., Drakulić Branko J., Zloh Mire F., Pecelj Jovana R., Popović Gordana V., Juranić Ivan O. |
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| Jazyk: | angličtina |
| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | Journal of the Serbian Chemical Society, Vol 72, Iss 12, Pp 1201-1216 (2007) |
| Druh dokumentu: | article |
| ISSN: | 0352-5139 1820-7421 |
| DOI: | 10.2298/JSC0712201V |
| Popis: | The protolytic equilibria of 13 4-aryl-2,4-dioxobutanoic acids (ADKs) were spectrophotometrically studied in aqueous solutions in the pH range 1-9 at 25±1 °C and an ionic strength of 0.1 mol l-1 (NaCl), with the exception of the 4-OH-derivative which was also potentiometrically studied in the pH range 7-10 at 25±1 °C and an ionic strength of 0.1 mol l-1 (NaCl). In solution, the compounds simultaneously exist in one diketo and two enolic forms; therefore, the determined acidity constants (pKa1 1.87-2.29, pKa2 6.63-8.13 and pKa3(4-OH-) 9.52) represent system macro constants. The 1H-NMR spectrum of the parent compound (4-phenyl- -2,4-dioxobutanoic acid) (25 °C, pD 5.0) proved the existence of all tautomeric forms. Using the extended Hammett relation, the determined pKa values were correlated with literature σ values. The predicted pKa values were in fair accordance with the experimentally observed ones. Molecular, monoanionic and dianionic forms of the parent compound were optimized by the semi-empirical molecular orbital PM6 method using the implicit water solvation model (COSMO). The obtained geometries were used to explain the quality of the LFER models. |
| Databáze: | Directory of Open Access Journals |
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