A DFT study of the structures of pyruvic acid isomers and their decarboxylation

Abstract

Pyruvic acid and its isomers, including the enol tautomers and enantiomeric lactone structures, have been investigated at the B3LYP/6-311 + + G(3df,3pd) level, and it is found that a keto form with trans C(methyl)C(keto)C(acid)O(hydroxyl) and cis C(keto)C(acid)OH, and with one methyl hydrogen in a synperiplanar position with respect to the keto oxygen, is the most stable. This agrees with previous theoretical and experimental determinations. However, no minimum corresponding to protonated pyruvate could be located, although previous semiempirical calculations had found such structures. Decarboxylation by different possible routes was then studied. It was found that the direct formation of acetaldehyde, the most stable of the resulting C2H4O isomers, via a four-center-like transition state is the most feasible, although there is a high activation barrier of 70 kcal mol(-1). In contrast to semiempirical calculations, it is found that no hydroxyethylidene-carbon dioxide complex exists as a product, and no transition state leading to the dissociation to hydroxethylidene could be located.

Theoretical study on keto–enol tautomerism and isomerization in pyruvic acid

“…Also, keto–enol tautomerism and isomerization in pyruvic acid have been well studied experimentally and theoretically . Kakkar et al theoretically investigated the stability of isomers of pyruvic acid in the gas phase using the density functional theory. They found that a keto form with trans methylgroup‐C keto ‐C acid ‐O hydroxyl and cis C keto ‐C acid ‐O‐H, and one methyl hydrogen in a synperiplanar position with respect to the keto‐oxygen, is the most stable isomer.…”

“…Keto–enol tautomerism of pyruvic acid is mainly studied experimentally . The theoretical studies are almost related to the stability of pyruvic acid tautomers and isomers in the gas phase and solution . The keto–enol tautomerism processes between the enol and keto forms of pyruvic acid have not been studied, theoretically.…”

“…[3,7] The theoretical studies are almost related to the stability of pyruvic acid tautomers and isomers in the gas phase and solution. [9,10,14] The keto-enol tautomerism processes between the enol and keto forms of pyruvic acid have not been studied, theoretically. It has been established [10,14] that energy differences among some of its tautomers and isomers are very small so that they may interconvert at room temperature.…”

“…[9,10,14] The keto-enol tautomerism processes between the enol and keto forms of pyruvic acid have not been studied, theoretically. It has been established [10,14] that energy differences among some of its tautomers and isomers are very small so that they may interconvert at room temperature. Therefore, study of pyruvic acid tautomerism mechanisms and calculation of their activation energies is important.…”

Elimination Reactions

“…Decarboxylation of pyruvic acid and its isomers, including the enol tautomers and enantiomeric lactone structures, has been investigated at the B3LYP/6-311++G(3df, 3pd) level. 18 It has been found that a keto form with trans C methyl C keto C acid O hydroxyl and cis C keto C acid OH, and with one methyl hydrogen in a synperiplanar position with respect to the keto oxygen, is the most stable.…”