Spectroscopic and Theoretical Study on Isomerism, Prototautomerism, and Acid Dissociation Constants of 2-Hydroxy-3-(3-oxo-1-phenylbutyl)chromen-4-one

Abstract

The prototropic, tautomeric, and ionization equilibria of all of the structures of 2-hydroxy-3-(3-oxo-1-phenylbutyl)chromen-4-one (warfarin) were studied experimentally and theoretically. The structure elucidation and acidity constant determination along with the tautomeric equilibrium constants were carried out experimentally by a UV−visible spectroscopic method and theoretically investigated at the HF/6-31G(d) and B3LYP/6-31G(d) levels of theory. The obtained K a values were evaluated by structure elucidation and a protonation mechanism. Using the gauge-including atomic-orbital (GIAO) method for calculating 1H and 13C nuclear magnetic shielding tensors, the Hartree−Fock (HF) and density functional (DFT) levels of theory were applied to warfarin. Geometry optimizations were also performed on each species, and the absence of negative frequencies verified that all structures were true minima. Theoretical values were compared to the experimental data. Satisfactory agreement between the experimental chemical shifts and the theoretical values of shielding constants (calculated by GIAO/DFT and GIAO/HF methods) was obtained.

Potentiometric, Theoretical, and Thermodynamic Studies on Equilibrium Constants of Aurintricarboxylic Acid and Determination of Stability Constants of Its Complexes with Cu2+, Ni2+, Zn2+, Co2+, Hg2+, and Pb2+Metal Ions in Aqueous Solution

“…Semiempiric molecular orbital (SE-MO) methods are one of the theoretical calculations that will assist in comprehending the protonation sequence of phenolate and carboxylate groups in the ligand molecule. The method is very useful for determination of the order of protonation in polyprotic coordination molecules. − The formation heats ( H f ) and the total energies (TE) of the ligands and monoprotonated species were calculated by the Semi-Empirical AM1 method. In addition, the proton affinity (PA) of each oxygen atom in the ligands was found using formation heats in the following equation and given in Table . PA = 367.2 + Δ italicH normalf normal° ( B ) − Δ italicH normalf normal° ( BH + ) where PA is the proton affinity of B types; Δ H f °(B) is the formation heat of the B molecule; Δ H f °(BH + ) is the formation heat of the BH + molecule; and 367.2 is the formation heat of H + …”