The enols of acetic acid and methyl acetate

Guthrie, J. Peter; Li, Zhi

doi:10.1139/v95-173

Cited by 22 publications

(15 citation statements)

References 14 publications

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“…We will take the pK a of acetic acid enol as 8.1. This differs from a previous suggestion (16,18) that was based on the pK a of o-phenylphenol, 9.93 (28), implying that the phenyl would have a very small effect. There remains the question of why a phenyl substitutent has such different effects depending on environment.…”

Section: Resultscontrasting

confidence: 99%

“…This estimated free energy of transfer leads to a value of -9.64 ± 1.16 kcal/mol 2 for the free energy of formation of aqueous ketene. We previously reported (18) the free energy of formation of ketene hydrate (acetic acid enol) in aqueous solution as -67.90 ± 1.67 kcal/mol (16). Thus the free energy change upon covalent hydration of ketene to form ketene hydrate is ∆G°= -1.57 ± 2.03 kcal/mol, and the free energy change for hydration of ketene to acetic acid is ∆G°= -28.02 ± 1.16 kcal/mol.…”

Section: Resultsmentioning

confidence: 99%

“…The enol content of acetic acid has been determined by indirect thermodynamic calculations (16,18) and by molecular orbital calculations (54). The two approaches are in good agreement.…”

Section: Discussionmentioning

confidence: 95%

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The hydration of ketene and carbon dioxide: an examination of the kinetics in terms of No Barrier Theory

Guthrie¹

1999

Can. J. Chem.

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Rate constants for hydration of carbon dioxide and ketene can be calculated by applying No Barrier Theory, which needs only equilibrium constants and distortion energies, the latter calculated using molecular orbital theory. The calculated free energies of activation are in satisfactory agreement with experiment: the rms error in free energy of activation is 2.38 kcal/mol. These compounds can also be described using Marcus Theory or Multidimensional Marcus Theory using the transferable intrinsic barrier appropriate to simple carbonyl compounds; in this case the rms error in free energy of activation is 2.19 kcal/mol. The two methods agree on preferred mechanistic path except for uncatalyzed hydration of ketene where Multidimensional Marcus Theory leads to a lower activation free energy for addition to the C=O, while No Barrier Theory leads to a lower free energy of activation for addition to the C=CH 2 . A rate constant for hydroxide ion catalyzed hydration of ketene can be calculated and is in accord with preliminary experimental results.Résumé : On a calculé les constantes de vitesse d'hydratation du dioxyde de carbone et du cétène en utilisant la théorie sans barrière qui ne nécessite que les constantes d'équilibre et les énergies de distorsion; ces dernières sont calculées par la théorie des orbitales moléculaires. Les énergies libres d'activation calculées sont en bon accord avec les valeurs expérimentales : l'erreur sur l'énergie libre d'activation est de 2,38 kcal/mol. On peut aussi décrire ces composés à l'aide de la théorie de Marcus ou de la théorie multidimensionnelle de Marcus en utilisant la barrière intrinsèque transférable appropriée aux composés carbonylés simples; dans ce cas, l'erreur sur l'énergie libre d'activation est de 2,19 kcal/mol. À l'exception de l'hydratation non catalysée du cétène pour laquelle la théorie multidimensionnelle de Marcus conduit à une énergie libre d'activation plus faible pour l'addition au groupe C=O alors que la théorie sans barrière conduit à une énergie d'activation plus faible pour l'addition sur le C=CH 2 , les deux méthodes sont concordantes en ce qui a trait à la voie mécanistique préférée. On peut calculer une constante de vitesse pour l'hydratation du cétène catalysée par l'ion hydroxyde et elle est en accord avec les résultats expérimentaux préliminaires.Mots clés : cétène, dioxyde de carbone, hydratation, théorie de Marcus, théorie sans barrière.[Traduit par la Rédaction] Guthrie 942Can. J. Chem. 77: 934-942 (1999)

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Section: Resultscontrasting

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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The hydration of ketene and carbon dioxide: an examination of the kinetics in terms of No Barrier Theory

Guthrie¹

1999

Can. J. Chem.

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“…[10,11] The pK Enol values were experimentally estimated [6] and computed; [12,13] these are much higher than those of aldehydes and ketones. The pK Enol value for the parent CH 3 COOH/CH 2 =C(OH) 2 pair was estimated to be in the range of 18-21 [14,15] in reasonable agreement with the computed values of 19-25. [12,16,17] Enols of carboxylic acids have been intensively studied computationally and found to be substantially less stable than their acid tautomers.…”

supporting

confidence: 74%

1,1‐Ethenediol: The Long Elusive Enol of Acetic Acid

2020

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We present the first spectroscopic identification of hitherto unknown 1,1‐ethenediol, the enol tautomer of acetic acid. The title compound was generated in the gas phase through flash vacuum pyrolysis of malonic acid at 400 °C. The pyrolysis products were subsequently trapped in argon matrices at 10 K and characterized spectroscopically by means of IR and UV/Vis spectroscopy together with matching its spectral data with computations at the CCSD(T)/cc‐pCVTZ and B3LYP/6–311++G(2d,2p) levels of theory. Upon photolysis at λ=254 nm, the enol rearranges to acetic acid and ketene.

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“…This led to an interest in various ways to determine enol content by indirect extrathermodynamic means or by estimation. We have reported several such attempts . Reliable and accurate experimental results were obtained by Kresge et al .…”

Section: Introductionmentioning

confidence: 90%

Equilibrium constants for enolization in solution by computation alone

Guthrie

Povar

2013

J of Physical Organic Chem

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Equilibrium free energy changes for enolization in aqueous solution can be calculated with useful accuracy (rmse = 1.3 kcal/mol for 37 reactions). These calculations involve gas phase free energy changes calculated using the G3MP2B3 method and solvation energies calculated using the IPCM method corrected by a parameterization scheme which we have reported. For chloroacetones, we find a small preference for enolization to the halogenated side and a preference for forming an enol with Cl Z to the OH. This may be partly due to weak hydrogen bonding but must be partly due to a relief of crowding; 2-butanone also shows a preference for the Z-enol. There are serious disagreements between calculated and experimental values for some of the enolization equilibria of 1,3,5-cyclohexanetrione (phloroglucinol); we argue that the problems are with the experimental values. Reasonable values are obtained for the enolization of Meldrum's acid, diethyl malonate, and 1,3-cyclohexanedione. Computational equilibrium constants in aqueous solution are now viable as supplements to and checks on experiment.

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The enols of acetic acid and methyl acetate

Cited by 22 publications

References 14 publications

The hydration of ketene and carbon dioxide: an examination of the kinetics in terms of No Barrier Theory

The hydration of ketene and carbon dioxide: an examination of the kinetics in terms of No Barrier Theory

1,1‐Ethenediol: The Long Elusive Enol of Acetic Acid

Equilibrium constants for enolization in solution by computation alone

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