Equilibrium constants for keto-enol tautomerisation and migration of hydrogen from carbon to nitrogen to form enamine or zwitterion tautomers have been measured for 2-, 3and 4phenacylpyridines (PyCH,COPh) in aqueous solution at 25 "C. Relative tautomeric stabilities fall in the order ketoimine > enamine > enol and (for the 3-isomer) enol > zwitterion. Values of pKT, (-log KT) where KT = [enamin...

Proton tautomerism is a general phenomenon in organic molecules and plays a vital role in many fields of chemistry and biochemistry. The tautomerism of salicylideneanilines [eq(1)] has attracted a considerable attention because it is closely related to thermoand photochromism. Salicylideneanilines greatly favor the enol form over the cis-keto form in the gas phase. We demonstrate here that the ...

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 (ketoenol) of pyruvic acid, whereas the ketonization (ketoenol) is preferred ...

In the title compound C(14)H(17)N(3)O(2), the dihedral angle between the rings is 16.68 (13)°. Although the compound crystallizes in the keto form, the possibility of keto-enamine-enol-imine tautomerism is explained by a strong intra-molecular N-H⋯O hydrogen bond.

The mol-ecular structure of the title compound, C(8)H(12)N(2)O, indicates that 2-isopropyl-6-methyl-pyrimidin-4-ol (the enol-form) undergoes an enol-to-keto tautomerism during the crystallization process. The pyrimidin-4(3H)-one group is essentially planar, with a maximum deviation of 0.081 (1) Å for the O atom. In the crystal structure, symmetry-related mol-ecules are linked into centrosymmeti...

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 (ketoenol) of pyruvic acid, whereas the ketonization (ketoenol) is preferred ...

Structural diversification of canonical nucleic acid bases and nucleotide analogues by tautomerism has been proposed to be a powerful on/off switching mechanism allowing regulation of many biological processes mediated by RNA enzymes and aptamers. Despite the suspected biological importance of tautomerism, attempts to observe minor tautomeric forms in nucleic acid or hybrid nucleic acid-ligand ...