Change of the tautomeric preference for radical cation of pyruvic acid. DFT studies in the gas phase

Keto-enol tautomerism was investigated for ionized pyruvic acid using the DFT(B3LYP) method and the larger basis sets (6-31++G(d,p), 6-311++G(3df, 3pd) and aug-cc-pVDZ). Change of the tautomeric preference was observed when going from the neutral to ionized tautomeric mixture. Ionization favors the enolization process (keto→enol) of pyruvic acid, whereas the ketonization (keto←enol) is preferred for the neutral system. Ionization influences also π-electron delocalization, which increases exceptionally in the enol form, and slightly decreases in the keto form.