Intramolecular unsymmetrical oxygen-hydrogen-oxygen (OHO) bonds. Thermochemistry

Lazaar, K. I.; Bauer, S. H.

doi:10.1021/j100236a034

Cited by 30 publications

(20 citation statements)

References 1 publication

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“…The similar trends in C 1 , C b , and C a for the aliphatic cases are also consistent with a preference for b [5,[12][13][14][15][16]. For comparison, these equilibrium constants and those described below are collected in Table 7.…”

Section: Ultraviolet-vis Spectrophotometrysupporting

confidence: 65%

“…In one case, 1v, the NMR and UV K aÐb values are in good agreement. All of the methods rely ultimately on model compounds [7,8,11] but the NMR method involves time averaging of signals and therefore the necessity of using weighting factors [14,18]. Even though the NMR indicates a preference for b, the preference decreases when an aromatic group is introduced (cf.…”

Section: K Aðbmentioning

confidence: 99%

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Keto–enol and enol–enol tautomerism in trifluoromethyl-β-diketones

Sloop

Bumgardner

Washington

et al. 2006

Journal of Fluorine Chemistry

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Section: Ultraviolet-vis Spectrophotometrysupporting

confidence: 65%

Section: K Aðbmentioning

confidence: 99%

Keto–enol and enol–enol tautomerism in trifluoromethyl-β-diketones

Sloop

Bumgardner

Washington

et al. 2006

Journal of Fluorine Chemistry

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“…We found that the distance of the C⋅⋅⋅N bond becomes shorter and shorter from reactant ( 3 A ) to product ( 4 A ) via the intermediate TS 3A−4A in Figure S1, resulting from the formation of a C=N double bond. Keto‐enol tautomeric equilibrium is quite normal and the enolic form of 2,4‐pentanedione is mostly present in the gas phase and in solution due to the intramolecular hydrogen bond interactions in the enol isomer . In Figure , the enolic form of 2,4‐pentanedione is combined with 4 A by hydrogen bond interactions with the thiourea group of the catalyst, thus forming 5 A .…”

Section: Resultsmentioning

confidence: 99%

Theoretical Studies on the Mechanism of the Michael Addition Reaction Catalyzed by a Thiourea‐Cinchona‐Amine: Triple Activation

Zhou

Dang

2015

Asian J Org Chem

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This paper attempts to illuminate the mechanism of the catalytic Michael addition of 2,4-pentanedione with acrylaldehyde mediated by at hiourea-cinchona-amine catalyst via density functional theory calculations. The calculated results show that the CÀCc oupling easily occurs once the electronegative and electropositive sites of the reactants are generated by the catalyst. However,t he previously proposed mechanism with the formation of an imine from the carbonyl group of reactants and the amine group of catalyst fails due to high reactionb arriers for both the formation of the imine and the hydrolysis of the imine with water in order to regeneratet he catalyst. Instead,t he reactionp athways going throught he protonation of the amine in the catalyst and formationo fh ydrogen bonds betweent he reactants and catalyst have smaller barriers. Our study will be helpful in designing new catalysts or extending the substrate scope of the reaction.

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“…The individual chemical shifts of the carbon and proton atoms involving an intramolecular chemical exchange in the tautomerism are identified by the usual measurement. It has been reported that the ratio of two enolic tautomers of asymmetric β‐diketones depends on the solute concentration, temperature, and solvent . These dependences are influenced by the intermolecular hydrogen‐bonding effect .…”

Section: Introductionmentioning

confidence: 99%

“…Thus, the NMR signals of the magnetically nonequivalent atoms at the chemically exchanging position in the E‐E tautomerism are observed as a single line shape subject to broadening or sharpening. NMR measurements in the solid state,– a dilute solution of a low‐polarity solvent, and an anhydrous solution and calculation of the chemical shifts were performed to obtain the individual chemical shifts.…”

Section: Introductionmentioning

confidence: 99%

Suppression Mechanism for Enol–Enol Isomerization of 2‐Substituted Dimedones

2015

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2-Substituted dimedones,d escribed as having as imple chemical structure, are at ype of cyclic b-diketone with enol-enol interconversion. The influence of the enolenol isomerism interferes with structure analysiso fm any dimedones in solution by NMR spectroscopy. It was demonstrated that the isomerism of the 2-substituted dimedones depends on solvent, time, solute concentration,a nd temperature. Negativea ctivation energy of the isomerization was determinedb yt he NMR line shape and spin-spin relaxation analyses, which is an extraordinary phenomenon found for the first time in the molecular dynamics of NMR. Suppression of the isomerization by heating, dilution of the solute, and time control in severall ow-polarity solvents enabled analysiso ft he enol form in detail. It was clarified that deceleration of the intramolecular chemical exchange rate in the isomerization was responsible for the decrease in the intermolecular hydrogen-bonding effect in the suppression mechanism. Figure 1. E-E isomerism of a) asymmetric and b) symmetric b-diketones.[a] H.

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Intramolecular unsymmetrical oxygen-hydrogen-oxygen (OHO) bonds. Thermochemistry

Cited by 30 publications

References 1 publication

Keto–enol and enol–enol tautomerism in trifluoromethyl-β-diketones

Keto–enol and enol–enol tautomerism in trifluoromethyl-β-diketones

Theoretical Studies on the Mechanism of the Michael Addition Reaction Catalyzed by a Thiourea‐Cinchona‐Amine: Triple Activation

Suppression Mechanism for Enol–Enol Isomerization of 2‐Substituted Dimedones

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