Computational study of energies and structures of 2,4,6‐pyrimidinetrione and its anions

Abstract

Energies and structures of 2,4,6-pyrimidinetrione, its anion, dianion, and trianion have been studied by means of ab initio and density functional computations. According to these studies, the most stable among the molecular tautomers is the triketo form, followed by the 6-hydroxy tautomer, in full agreement with earlier theoretical results and with experimental data on the tautomeric equilibrium. The deprotonation energy of 1345.24 kJ mol Ϫ1 calculated for 2,4,6-pyrimidinetrione, corresponds to a moderately strong COH acid, in accordance with its experimental pK a 1 ϭ 8.4 (solvent dimethylsulfoxide). The calculated structural changes, caused by the molecule 3 monoanion conversion, are in good agreement with those found experimentally. Energy and structural changes, worked by both anion 3 dianion and dianion 3 trianion conversions, have also been computed and discussed.

IR spectral and structural studies of 4‐aminobenzenesulfonamide (sulfanilamide)‐d0, ‐d4, and ‐15N, as well as their azanions: Combined DFT B3LYP/experimental approach

“…This rule is also valid for the bond angles (Table IX); it agrees with the data for carbanions, oxyanions, and other azanions (Refs. [10,13,14,19,34] and references therein). …”

“…The charge change values ⌬q i ϭ q i (anion) Ϫ q i (molecule) are usually quite informative in showing the distribution of the new (e.g., carbanionic, azanionic) changes in anions (Refs. [10,11,13,14,19,20,28,29,34] and references therein). According to the present calculations, the new (azanionic) charge of 2a is distributed, as follows: 0.08e Ϫ , 0.23e Ϫ , and 0.12e Ϫ are delocalized over the amino, phenylene, and sulfonyl groups, respectively, and 0.57e Ϫ remain localized at the azanionic center (cf.…”

DFT and experimental study on the IR spectra and structure of 2-hydroxy-3-methoxybenzaldehyde (o-vanillin) and its oxyanion

“…The DMSO as polar aprotic solvent usually de- Table 2. The agreement between the experimental and calculated values is very good -the mean absolute deviation between observed and calculated frequencies is 16.5 cm À1 , which value is not away from the low border of the 15-25 cm À1 interval of deviations, typical for the DFT calculations for molecules containing carbonyl or cyano groups [19][20][21][22][23][24][25][26][27].…”

“…Table 1 Total energies (E), Gibbs free energies (G), zero-point vibrational energy (ZPVE) and relative energies (E rel ) of conformers of o-vanillin and its anion. acidities in polar aprotic solvents [19][20][21][22][23][24][25][26] (and references therein): low E D 's high acidities low pK a values.…”

Thermochemistry of organic molecules: The way to understand energy–structure relationships

“…All ab initio and DFT theoretical calculations [38][39][40][41][42][43][44] report the triketo tautomer to be the most stable one in the gas phase. In the solid state, the anhydrous compound exists only as the triketo form [39,45,46].…”