For barbituric acid and thiobarbituric acid, the pKas of the hydrogens bonded to carbon and the hydrogens bonded to nitrogen in each system are computed using an isodesmic reaction with a reference acid. Isodesmic reactions conserve bond number and bond type. Optimum equilibrium geometries, harmonic vibrational frequencies, and the corresponding Gibbs free energies are computed for all of the reactants and products in each isodesmic equation using SCF theory and density functional theory. The DFT functionals employed are Becke's three-parameter hybrid functional using the LYP correlation functional, the M06-2X high nonlocality hybrid functional from Thular and Zhao, and the ?B97XD functional from Head-Gordan and coworkers which includes empirical dispersion. The basis sets employed are Dunning and coworkers' correlation consistent basis sets, aug-cc-pVDZ and aug-cc-pVTZ. The solvation model used is the continuous surface charge formalism for the polarizable continuum model (PCM). Results are presented for different levels of theory and for different basis sets to determine what level of computation is needed for consistent results. In addition, the effect of employing different reference acids is investigated.

Computing acidities of barbituric and thiobarbituric acid

247th National Meeting (2014)

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