The nature of intramolecular hydrogen bond in 2-nitromalonaldehyde

Thermodynamic and kinetic effects of Lewis acid complexation on a Schiff base present in two tautomeric forms

“…The geometry of the tautomers and hydrogen transfer transition states has been optimized with the hybrid functional B3LYP 25, 26. The 6‐31+G(d,p) basis set27 has been used in combination with the B3LYP functional because it has been shown to provide a good geometrical and electronic description of hydrogen bonded systems 28–33. Frequency calculations have been carried out at the same computational level to verify that the structures obtained correspond to energetic minima or true transition states.…”

Comparison of Tautomerization, Vibrational Spectra and UV-Vis Analysis of β-Ketoester With Acetylacetone. An Experimental and Theoretical Study

“…Cook and Feltman determined the tautomeric composition of AA in the liquid phase by 1 H NMR: AA (neat; 80% enol), (chloroform; 86% enol(, (DMSO; 63% enol) [17]. 1 H NMR shows that the enol form of AA prevails in the both gas and liquid phase (in inert solvents) at all temperatures. In these conditions, a strong hydrogen bond is created that can stabilize the enol tautomer [16].…”

“…Thermodynamic factors of enol and keto forms for methyl acetoacetate (MAA) (R1=CH3, R2=H, and R3=CH3) obtained from a van't Hoff equation integrated by 1 H NMR results are G 0 (g) = G 0 (keto) -G 0 (enol) = 0.08 kcal.mol -1 , S 0 (g)= 9.93 cal.mol -1 .K -1 , H 0 (g)= 3.04 kcal.mol -1 in the gaseous phase and G 0 (l) = -1.89 kcal.mol -1 , S 0 (l)= 6.07 cal.mol -1 .K -1 , H 0 (l)= -0.08 kcal.mol -1 in the liquid phase [11]. These outcomes show that decreasing temperature ranges increases equilibrium constants and leads to a great enol content of methyl acetylacetone, which is energetically favored in the gas phase.…”

“…Under usual conditions when one tautomer is more stable than the others, it is known as the "stable form". An intramolecular hydrogen bond is present in closed cis-enol forms of -dicarbonyl and it leads to a stable form of the tautomer [1][2].…”

“…The results showed that acetylacetone reacted faster with formaldehyde than methyl acetoacetate. Fokendt et.al, using 1 H NMR spectroscopy, investigated the intermolecular tautomeric interaction of keto-enol -dicarbonyl compounds [11]. They found that the proton chemical shift of enol form in acetylacetone (AA), methyl acetoacetate (MAA) and, ethyl acetoacetate (EAA) in the pure liquid phase, is 14.6, 11.96, 11.6 ppm, and in the gas phase, is 15.2, 11.97, 12.01 ppm, respectively.…”