Keto/enol tautomerism in phenylpyruvic acids: structure of the o-nitrophenylpyruvic acid

Experimental (FT-IR) and theoretical (DFT-IR) studies of keto–enol tautomerism in pyruvic acid

“…more than 300 times for o-nitrophenylpyruvic acid, variation from 0.17 (gas phase-ab initio calculations) to 59% (DMSO-NMR experiment) [15]}, one may suppose that at least four isomers (Tce, Tte, Cte and E1) may be present in the mixture of tautomers-rotamers in solution.…”

“…The enol form of acid has been signalled in 1981 by Ray et al as possibly present in IR spectrum of the pure liquid phase of pyruvic acid [13]. In the case of solid b C-aryl [14,15] and b C-heteroaryl derivatives of pyruvic acid [16,17], the enol form has recently been proved by IR, NMR and X-ray experiments.…”

Temperature-variable NMR Study of the keto-enol Tautomerism of Phenylpyruvic Acid

“…The enthalpy, ΔH 0 , and entropy, ΔS 0 , for the conversion of the keto to enol form were obtained by the van't Hoff equation, as follows: 11,16 ln ,…”

“…Many spectroscopic studies, ultra violet (UV), infrared (IR), Raman and nuclear magnetic resonance (NMR) studies, have been reported on the keto-enol tautomerism [3][4][5][6][7][8][9][10][11][12] and conformation 6,9,10,12,13 of PA and PPA. These many investigations have revealed that these compounds exist as equilibrium mixtures consisting of the keto and enol forms.…”

“…Carpy et al assigned the structures of the two tautomeric forms of PPA in DMSO solvent by 1 H and 13 C NMR spectroscopy, and found by X-ray crystallography of the single crystal that the crystalline form takes the keto isomer. 11,12 Moreover, the substituent effect on the tautomeric equilibrium was studied by using ab initio calculations in the gas phase, and the thermochemical parameters were obtained. They confirmed a large preference for the enol isomer relative to the keto isomer for PPA and o-chloro PPA.…”