Search results for "Keto–enol tautomerism"
showing 10 items of 11 documents
Gold/Isophorone Interaction Driven by Keto/Enol Tautomerization
2016
The binding behavior of isophorone (C9H14O) to Au adatoms and clusters deposited on MgO/Ag(001) thin films is investigated by scanning tunneling microscopy (STM) and density functional theory (DFT). The STM data reveal the formation of various metal/organic complexes, ranging from Au1/isophorone pairs to larger Au aggregates with molecules bound to their perimeter. DFT calculations find the energetically preferred keto-isophorone to be unreactive toward gold, while the enol-tautomer readily binds to Au monomers and clusters. The interaction is governed by electrostatic forces between the hydroxyl group of the enol and negative excess charges residing on the ad-gold. The activation barrier b…
Isotopic Effect on the Kinetics of the Belousov-Zhabotinsky Reaction
2007
In this work we present results about the deuterium isotope effect on the global kinetics of a Belousov-Zhabotinsky reaction in batch conditions. A nonlinear dependence of the Induction Period upon the percentage of deuterated reactants was found. The isotopic effect on the bromination reaction of malonic acid was evaluated.
Ab initioanalysis on metal ion catalysis in the enolization reactions of some acetylheterocycles: kinetics of the enolization reactions of 3-acetyl-5…
2002
Kinetic data on the enolization reaction of 3-acetyl-5-methylisoxazole, 5-acetyl-3-methylisoxazole, 3(5)-acetylpyrazole and some previously studied acetylheterocycles have been the object of a comprehensive ab initio analysis. Enolization rate constants were measured spectrophotometrically by the halogen trapping technique at 25 °C and ionic strength of 0.3 mol dm−3 in water, in acetate buffers, in dilute hydrochloric acid, in dilute sodium hydroxide and in the presence of some metal ion salts. In the spontaneous (water) and base (acetate) catalysed reactions the ketones investigated are generally more reactive than acetophenone, according to the electron-withdrawing effect of the heterocyc…
1H,13C and17O NMR study of substituted nitropyridines
1991
1H, 13C and 17O NMR spectra for 22 substituted nitropyridines were measured and their 1H NMR spectra were analysed. The most significant variations in the NMR parameters are found for isomeric hydroxy derivatives, owing to the possibility of keto–enol tautomerism. The prevalence of the keto form is observed in 2- and 4-hydroxy derivatives, while the 3-hydroxy derivative exists in its enol form. Among the three nuclei studied, 17O seems to be the best nucleus for probing the keto–enol tautomerism. No correlation is observed between the torsion angle of the nitro group and its 17O NMR chemical shift. Molecular mechanics calculations were performed to clarify the torsional energetics of the ni…
Antidiabetische wirkstoffe, IV [1] trifluormethylsubstituierte 2-(4-toluidino)pyrimidine
1985
Zusammenfassung Durch Umsetzung von 4-Tolylguanidin mit den entsprechenden fluorierten β-Diketonen in Gegenwart von Natriumcarbonat im Schmelzfluβ sind die folgenden 4-Trifluormethyl-2-(4-toluidino) pyrimidine zuganglich gemacht worden: die 6-Methyl-, 6-Ethyl-, 6-Isopropyl-, 6-tert. Butyl- und 6-Isopentyl-Abkommlinge. Zur Charakterisierung der dargestellten Verbindungen sind IR-, 1H-NMR- und MS-Daten herangezogen worden. In dem neuen Strukturtyp sind besonders antidiabetische, antimykotische, trichomonazide und herbizide Wirksamkeit ausgepragt.
Antineoplastika XVI [1]. 4-Alkyl-6-trifluormethyl-2-ureidopyrimidine
1985
Zusammenfassung Bei der Umsetzung von Dicyandiamid mit Trifluormethyl- gruppen tragenden β-Diketonen entstehen die korrespondierenden 4-Alkyl-6-trifluormethyl-2-ureidopyrimidine. So wird mit 1,1,1-Trifluor-2,4-pentandion das 4-Methyl-6-trifluormethyl- 2-ureidopyrimidin, mit 1,1,1-Trifluor-2,4-hexandion das 4- Ethyl-6-trifluormethyl-2-ureidopyrimidin, erhalten. Die Struktur der Endprodukte wird dutch die IR-, 1 H-NMR-, 13 C-NMR- und Massenspektren charakterisiert.
Stereoelectronic Requirements for Optimal Hydrogen-Bond-Catalyzed Enolization
2011
Protein crystallographic analysis of the active sites of enolizing enzymes and structural analysis of hydrogen-bonded carbonyl compounds in small molecule crystal structures, complemented by quantum chemical calculations on related model enolization reactions, suggest a new stereoelectronic model that accounts for the observed out-of-plane orientation of hydrogen-bond donors (HBDs) in the oxyanion holes of enolizing enzymes. The computational results reveal that the lone-pair directionality of HBDs characteristic for hydrogen-bonded carbonyls is reduced upon enolization, and the enolate displays almost no directional preference for hydrogen bonding. Positioning the HBDs perpendicular to the…
Syntheses with organoboranes. Part 14: Enolization–aldolization of conjugated cyclohexenones via dienolborinates
2002
Abstract Enolization of cyclohex-2-enone ( 1 ), 3-methyl- ( 2 ), 3,5-dimethyl- ( 3 ), 3,5,5-trimethyl- ( 4 ), and 3,4,5,5-tetramethylcyclohex-2-enone ( 5 ) with chlorodicyclohexylborane proceeds by deprotonation at the 6-position. Aldolization of the dienolborinates with benzaldehyde, and acetaldehyde, provides the corresponding anti aldols with 87–95% selectivity. Ketones 4 and 5 undergo competitive deprotonation at the 3-methyl group and aldolization at the 2-position. In contrast, lithium dienolates derived from 4 and 5 gave syn aldols with 95% selectivity.
Chlorodicyclohexylborane-mediated aldol additions of alpha,alpha'-dioxygenated ketones.
2001
Boron aldol additions of variously O-protected alpha,alpha'-dioxygenated ketones using dicyclohexylboron chloride and a tertiary amine have been investigated. The stereoselectivity of the process was dependent on the protecting group on the alpha-oxygen atoms. Notably, ketones with bulky silyloxy groups gave syn aldols, most likely via Z enolates. This rules out the participation of chelates during the enolization process, at least in the presence of such sterically crowded protecting groups. An alternative explanation is offered.
Durch sterische effekte stabilisierte ß-ketocarbonsäuren
1989
Abstract Increasing steric hindrance in β-keto carboxylic acids leads to an increasing kinetic stability towards decarboxylation, till systems are reached which are completely stable at room temperature. Simultaneously the tautomeric equilibrium is changed in favour of the (Z)-enol, and finally in favour of the (E)-configurated enol.