Energetics of Fluoroalkene Double Bond Isomerizations

Lindner, Patrick E.; Lemal, David M.

doi:10.1021/ja963789f

Cited by 12 publications

(9 citation statements)

References 33 publications

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“…14 Interestingly, Lemal has determined ∆H enol for several highly fluorinated ketones. 31 Unfortunately, these values are strongly affected by the fluorine atom directly attached to the carbon-carbon double bond 32 and cannot be directly compared to data in the present study.…”

Section: Resultsmentioning

confidence: 83%

Enols and Enolates of Carboxylic Acid Derivatives. A G2(MP2) ab Initio Study

Rosenberg

1998

J. Org. Chem.

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The effect of substituents on the stability of enols and enolates relative to their oxo (CO) forms is explored using the G2(MP2) ab initio method for CH3COX (14 substituents). Calculated enthalpies of reaction for enolate formation agree well with experimental gas-phase data. Relative to acetaldehyde, enolate formation from a carbonyl compound is favored by the presence of both σ and π electron-withdrawing groups and disfavored by π-donating groups. Isodesmic reactions show that electron withdrawal stabilizes the enolate more than the oxo form. Donation from the π system stabilizes the oxo form but has little or no effect on the enolate form. Destabilization due to electrostatic repulsion between the oxygen bound carbon and the attached atom for X = {CF3, CHO, C⋮N} is more severe in the oxo than enolate form. The effect of substituents on the stability of both enolates, H2CC(O-)X, and ethoxide derivatives, CH3CH(O-)X, are shown to be very similar. Relative to acetaldehyde, the heats of reaction of CH3COX for both enolate formation and hydride addition are also similar. For enols, both σ electron-withdrawing and π-donating substituents favor the oxo over the enol form. Isodesmic reactions show that substituents have a parallel effect on stability in the oxo and enol forms, as well as in ethene derivatives. The magnitude of these effects increases with the polarity of the double bond, i.e., carbonyls > enols > ethenes. To summarize substituent effects, enols can be thought of as ethene derivatives which are slightly polarized by the hydroxy group, while enolates can be thought of as ethoxide derivatives which are perturbed by the double bond.

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Section: Resultsmentioning

confidence: 83%

Enols and Enolates of Carboxylic Acid Derivatives. A G2(MP2) ab Initio Study

Rosenberg

1998

J. Org. Chem.

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“…Aluminum enolates can also be synthesized by reaction of highly halogenated ketones with activated metal 81 . From a thermochemical perspective, CF 3 C(=O)CF 2 X (X = Cl, Br, O 3 SF) results in loss of the X group (weaker C−X bond but also weaker Al-X bond) and fluorinated enols are often more stable than the corresponding ketones 82 , unlike their hydrocarbon counterparts where CH 2 replaces C=O.…”

Section: Group 13: Aluminum Gallium Indium and Thalliummentioning

confidence: 99%

Thermochemical Considerations of Metal Enolates

Liebman

Slayden

2010

Patai's Chemistry of Functional Groups

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Introduction Group 1: Lithium, Sodium, Potassium, Rubidium and Cesium Group 2: Beryllium, Magnesium, Calcium, Strontium and Barium Group 13: Aluminum, Gallium, Indium and Thallium Group 14: Tin and Lead Group 11: Copper, Silver and Gold Group 12: Zinc, Cadmium and Mercury Group 3: Scandium, Yttrium and the Lanthanides Actinides Group 4: Titanium, Zirconium and Hafnium Group 5: Vanadium, Niobium and Tantalum Group 6: Chromium, Molybdenum and Tungsten Group 7: Manganese and Rhenium Group 8: Iron, Ruthenium and Osmium Group 9: Cobalt, Rhodium and Iridium Group 10: Nickel, Palladium and Platinum

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“…This shift in the equilibrium has been attributed to the destabilization of the ketone through the electron withdrawal induced by the neighboring fluoro groups . Lemal and Lindner studied computationally the optimized structures of 2 – 4 to understand why the propensity for the enol tautomer increases as the ring size of the perfluorinated cyclic keto–enol systems decreases . They noted that the distance between the vinyl and allylic fluorine atoms increases as the ring size of the perfluorinated cyclic enol systems becomes smaller, and they attributed the increased presence of the enol tautomer to the weaker fluorine–fluorine steric repulsions in smaller cyclic systems.…”

Section: Introductionmentioning

confidence: 99%

Hyperconjugative π → σ*_CF Interactions Stabilize the Enol Form of Perfluorinated Cyclic Keto–Enol Systems

2019

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Lindner and Lemal showed that perfluorination of keto-enol systems significantly shifts the equilibrium toward the enol tautomer. Quantum mechanical calculations now reveal that the shift in equilibrium is the result of the stabilization of the enol tautomer by hyperconjugative π → σ* CF interactions and the destabilization of the keto tautomer by the electron withdrawal induced by the neighboring fluorine atoms. The preference for the enol tautomer further increases in smaller perfluorinated cyclic keto-enol systems. This trend is in contrast to the nonfluorinated compounds, where the enol is strongly disfavored in the smaller rings. The fluoro effect overrides the effect of the ring size that controls the equilibria in nonfluorinated compounds. The increased overlap of the enol π bond with the σ* CF orbitals of the allylic C-F bonds results in the increased preference for the enol tautomer in smaller perfluorinated keto-enol systems. We show here why the effect is much greater than in 3,3-difluorocyclooctyne.

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Energetics of Fluoroalkene Double Bond Isomerizations

Cited by 12 publications

References 33 publications

Enols and Enolates of Carboxylic Acid Derivatives. A G2(MP2) ab Initio Study

Enols and Enolates of Carboxylic Acid Derivatives. A G2(MP2) ab Initio Study

Thermochemical Considerations of Metal Enolates

Hyperconjugative π → σ*_CF Interactions Stabilize the Enol Form of Perfluorinated Cyclic Keto–Enol Systems

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Energetics of Fluoroalkene Double Bond Isomerizations

Cited by 12 publications

References 33 publications

Enols and Enolates of Carboxylic Acid Derivatives. A G2(MP2) ab Initio Study

Enols and Enolates of Carboxylic Acid Derivatives. A G2(MP2) ab Initio Study

Thermochemical Considerations of Metal Enolates

Hyperconjugative π → σ*CF Interactions Stabilize the Enol Form of Perfluorinated Cyclic Keto–Enol Systems

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Hyperconjugative π → σ*_CF Interactions Stabilize the Enol Form of Perfluorinated Cyclic Keto–Enol Systems