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Synthesis, determination of pK<inf>a</inf> values and GIAO NMR calculations of some new 3-alkyl-4-(p-methoxybenzoylamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones

Abstract:

3-Alkyl-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones (2) reacted with p-methoxybenzoyl chloride to afford the corresponding 3-alkyl-4-(p-methoxybenzoylamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (3). Five newly synthesized compounds have been characterized by elemental analyses, IR, 1H NMR, 13C NMR and UV spectral data. The newly synthesized compounds 3 were titrated potentiometrically with tetrabutylammonium hydroxide in four non-aqueous solvents such as acetonitrile, isopropyl alcohol, tert-butyl alcohol and N,N-dimethylformamide, and the half-neutralization potential values and the corresponding pKa values were determined for all cases. Thus, the effects of solvents and molecular structure upon acidity were investigated. In addition, isotropic 1H and 13C nuclear magnetic shielding constants of compounds 3 were obtained by the gauge-including-atomic-orbital (GIAO) method at the B3LYP density functional level. The geometry of each compound has been optimized using the 6-311G basis set. Theoretical values were compared to the experimental data. © 2007 Elsevier B.V. All rights reserved.