106259-98-7Relevant academic research and scientific papers
Substituent and temperature controlled tautomerism of 2-phenacyl-pyridine: The hydrogen bond as a configurational lock of (Z)-2-(2-hydroxy-2-phenylvinyl)pyridine
Kolehmainen, Erkki,Osmiaowski, Borys,Nissinen, Maija,Kauppinen, Reijo,Gawinecki, Ryszard
, p. 2185 - 2191 (2007/10/03)
2-Phenacylpyridines substituted in the benzene ring are in equilibrium with (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines when dissolved in chloroform. The substituent affects significantly the tautomeric equilibrium [the amount of the enolimine form stabilized by the intramolecular hydrogen bond is 1 and 92% for R = p-N(CH2)4 and p-NO2, respectively]. The negative logarithm of the tautomeric equilibrium constant, KT, is linearly dependent on the Hammett σ substituent constants. The dependence of KT vs. temperature is exponential in character: the more electron-withdrawing is the substituent, the more distinct is the influence of temperature. Unexpectedly, the tautomer present in the crystalline state is not the same for all compounds studied (it is the ketimine one for those carrying strong electron-donor groups). Among the different ab initio methods used to calculate the enthalpy of the proton transfer in chloroform solution, MP2/6-31G** gives the best results.
Keto-Enol and Imine-Enamine Tautomerism of 2-, 3- and 4-Phenacylpyridines
Carey, A. R. Edwin,Eustace, Stephen,O'Ferall, Rory A. More,Murray, Brian A.
, p. 2285 - 2296 (2007/10/02)
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-, 3- and 4-phenacylpyridines (PyCH2COPh) in aqueous solution at 25 deg 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=/ or /, are 1.05, 5.87 and 2.42 for the enamine or zwitterion tautomerism and 2.0, 4.86 and 4.4 for keto-enol tautomerism of the 2-, 3- and 4-isomers respectively.For the enamines KT was determined kinetically by quenching the enolate anion at a pH below its pKa and monitoring its relaxation to the ketoimine spectrophotometrically: combining rate constants for this process and the reverse reaction measured by halogen trapping of the enol or enamine gave KT.Values are compared with results of earlier indirect measurements by Katritzky.For the 3-isomer, the N-methyl-3-phenacylpyridinium ion was taken as a model for the zwitterion tautomer and a ratio of enol to zwitterion concentrations of 10:1 was derived from kinetic and equilibrium ionisation measurements corrected for a methyl substituent effect.The unusually large enol content of 2-phenacylpyridine in non-polar solvents was measured spectrophotometrically and extrapolated to water.For the 4-isomer the enol content could be obtained from a correlation of pKas of phenacylpyridine enols and vinylogously related phenols.Acidic and basic pKas of all tautomers are reported including kinetically determined values for O-protonation of the enaminones.Proton activating factors for ionisation and tautomerisation have been calculated andare compared with values for the vinylogous hydroxypyridines.The influence of charge delocalisation and electrostatic interactions on the stability of enolate and carboxylate anions is discussed.
Enol Content of α-Pyridyl- and Pyridinio-acetophenones
Carey, A. R. Edwin,Al-Quatami, Shaikha,O'Ferrall, Rory A. More,Murray, Brian A.
, p. 1097 - 1098 (2007/10/02)
A comparison of the effects of phenyl, pyridyl, and pyridinio substituents upon keto-enol tautomerisation and enol ionisation equilibria of acetophenone shows that polar effects upon bond hybridisation and resonance interaction with 'neutral' double bonds are important influences upon enol stability.
TAUTOMERISM OF AZINE DERIVATIVES. 11. 14N-NMR AND 17O-NMR INVESTIGATION OF INTRACHELATE TAUTOMERISM OF ACYLMETHYLPYRIDINES
Lapachev, V. V.,Stekhova, S. A.,Mainagashev, I. Ya.,Fedotov, M. A.,Khall, V. E.,Mamaev, V. P.
, p. 633 - 639 (2007/10/02)
Intrachelate -sigmatropic tautomerism in a series of acylmethylpyridines has been studied by 14N- and 17O-NMR specroscopy.Principles of tautomer modelling or simulation have been proposed and examined, nitrogen ond oxygen chemical shift spectra have been determined, and the accuracy of this method for the determination of tautomer composition has been evaluated.The presence of acceptor (electron withdrawing) substituents in the acylmethyl side-chain fragment has been found to stabilize the NH-tautomer.
