Energetics of acetic acid enol in aqueous solution. A new method for thermodynamic estimation

Guthrie, J. Peter

doi:10.1139/v93-263

Cited by 29 publications

(22 citation statements)

References 25 publications

(30 reference statements)

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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%

“…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%

“…Although intrinsic barriers are approximately transferable within families of "similar" reactions, they cannot be expected to remain independent of major changes in structure. The closest available values are the intrinsic barrier for addition of water (or hydroxide) to carbonyl compounds, for which a value of 7.36 was found to be a good average value (36), and the intrinsic barrier for protonation of an enol ether, for which a value of 12.3 was found (18).…”

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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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%

“…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%

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: 75%

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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“…104 An alternative estimation starts from the pK a for acetone enol, 10.94. 77 Using the general estimation procedure for r* proposed by Perrin et al, 101 we take r* = 3.2; s* for CH 3 is 0.0 and s* for OH is 1.34.…”

Section: Pk a Values For Acetic Acid Enolmentioning

confidence: 99%

Rate constants for decarboxylation reactions calculated using no barrier theory

et al. 2010

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No barrier theory (NBT) provides both a qualitative way of thinking about what makes a reaction fast or slow and a quantitative way of calculating the rate constant (free energy of activation) corresponding to a particular mechanism. The origin and development of this idea are reviewed and examples of its use for qualitative understanding are presented before applying it to a set of decarboxylations. From the literature, a set of best values for rate constants for decarboxylation was picked. Detailed mechanistic models were developed for reactions leading to delocalized ''anions'' or to localized anions. It was necessary to have pK a values for ionizaion of the carbon acids corresponding to all of these species and these were selected from the literature or estimated by linear free energy relations (or occasionally calculated from proton exchange data). Over the entire range of measured decarboxylation rate constants, a range of 10 25 in rate constant, the calculated values were in good agreement with experiment, with two exceptions: malonate dianion, which has been reported but probably not measured, and glycine, where it is possible that a different mechanism is being followed, unfortunately, one which we do not yet know how to treat by NBT. NBT is both a qualitatively and quantitatively useful tool for understanding chemistry.Résumé : La théorie sans barrière fournit d'une part une façon qualitative de réfléchir sur ce qui fait qu'une réaction est rapide ou lente et d'autre part une façon quantitative de calculer la constante de vitesse (énergie libre d'activation) correspondant à un mécanisme particulier. On passe en revue l'origine et le développement de cette idée et on présente des exemples de son utilisation dans la compréhension qualitative avant de l'appliquer à un ensemble de décarboxylations. On a tiré de la littérature un ensemble des meilleures valeurs pour les constantes de vitesse de décarboxylation. Des modèles de mécanismes réactionnels détaillés ont été développés pour des réactions conduisant à des anions délocalisés ou localisés. Il était nécessaire d'avoir les valeurs de pK a pour l'ionisation des acides carboniques correspondants à chacune des espèces et celles-ci ont été sélectionnées à partir de la littérature ou elles ont été évaluées par des relations d'énergie linéaires ou elles ont été occasionnellement calculées à partir de données d'échange de proton. Sur l'ensemble complet des constantes de vitesse de décarboxylation, une plage de constantes de vitesse relatives s'étalant de 1 à 10 25 , les valeurs calculées ont en bon accord avec les valeurs expérimentales, à deux exceptions près: le dianion de l'acide malonique a été rapporté, mais qui n'a probablement pas été mesuré et la glycine pour laquelle il est possible qu'un mécanisme différent soit impliqué, un mécanisme qu'on ne peut malheureusement pas encore traiter par la théorie sans barrière. La théorie sans barrière (TSB) est un outil qualitativement et quantitativement utile pour la compréhension de la chimie.Mots-clés : décarbox...

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Energetics of acetic acid enol in aqueous solution. A new method for thermodynamic estimation

Cited by 29 publications

References 25 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

Rate constants for decarboxylation reactions calculated using no barrier theory

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