Valence isomerization equilibria of highly fluorinated cycloocta-1,3,5-trienes

Rahman, M. M. A. Abdel; Secor, Beth A.; Morgan, Kimberly J.; Shafer, Paul R.; Lemal, David M.

doi:10.1021/ja00172a011

Cited by 14 publications

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“…Thus, the exo-H configuration is by far the more stable one. Probably the chief reason is smaller dipole−dipole repulsion in this stereoisomer between the C 3 −F bond and neighboring C−F bonds …”

Section: Resultsmentioning

confidence: 99%

Novel Keto−Enol Systems: Cyclobutane Derivatives

et al. 1996

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3H-Perfluorobicyclo[2.2.0]hexan-2-one (3) has been synthesized from hexafluorobenzene and equilibrated with its enol form (4). In carbon tetrachloride K e/k = 0.07 ± 0.01 (25 °C), but in Lewis basic solvents (e.g. acetonitrile, ether, and tetrahydrofuran) only enol is detectable at equilibrium because of its strength as a hydrogen bond donor. In the monocyclic counterpart of this keto−enol system, 2H-perfluorocyclobutanone (1) and perfluorocyclobut-1-enol (2), the enol is more stable yet. Here ketone is undetectable under equilibrating conditions in all media examined, including carbon tetrachloride. Among unhindered and unconjugated enols, 2 and 4 are more stable relative to their ketones than any others that have been reported. Ab initio quantum mechanical calculations support the conclusion that destabilization of the ketones, but not stabilization of the enols, by fluorine substitution is responsible for the unique relative stability of these enols.

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Section: Resultsmentioning

confidence: 99%

Novel Keto−Enol Systems: Cyclobutane Derivatives

et al. 1996

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“…There has been considerable interest in the effect of fluorine substitution on the energies of small ring compounds . If stabilization is found, it will have significant consequences for the synthesis of the more highly strained compounds.…”

Section: Introductionmentioning

confidence: 99%

Effect of Fluorine Substitution on the Energies of Small Ring Compounds

Wiberg

Márquez

1998

J. Am. Chem. Soc.

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The effect of fluorine substitution on the energies of small ring compounds has been examined via ab initio calculations at the MP2/6-31G*, MP2/6-311+G*, and B3LYP/6-311+G* theoretical levels, along with correction for differences in zero-point energies. The introduction of a fluorine into a cyclopropane ring leads to destabilization, which results from the higher s character in the orbitals forming the bonds to a substituent. On the other hand, this is not seen with cyclopropene. The effect of 3-substituents on cyclopropene was examined by studying cyclopropenone, cyclopropenethione, methylenecyclopropene, and 3,3-difluorocyclopropene. The stabilization was largest and about equal with the O and S substituents. Smaller effects were observed with CH2 and F2 substituents. The nature of the effects was studied making use of electron density difference maps. The structures and energies of the series of C4H4 and C4F4 derivatives were studied at the above theoretical levels. In most cases, fluorine substitution led to stabilization with respect to but-3-en-1-yne, but with tetrahedrane there was considerable destabilization. Fluorine substitution leads to destabilization of cyclobutyne with respect to cyclobutene.

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“…Surprisingly, these values are indistinguishable from those for the parent hydrocarbon. 54 The amount of 10 in equilibrium with 6 at 20 °C was found to be 0.2(8)%, 55 as compared with 0.01% for the hydrocarbon parent of 10 at 100 °C. Gamma irradiation at 77 K of cyclooctatetraene 6 in a 2-methyltetrahydrofuran glass by Williams et al generated the radical anion 64, which gave upon warming to 145 K an isotropic ESR spectrum comprising nine lines with binomial intensity distribution.…”

Section: Syntheses Based On Photocycloaddition To Alkenesmentioning

confidence: 93%

Hexafluorobenzene Photochemistry: Wellspring of Fluorocarbon Structures

Lemal

2001

Acc. Chem. Res.

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Ultraviolet irradiation of hexafluorobenzene in the vapor phase gives exclusively its Dewar valence isomer, from which a wealth of highly fluorinated compounds has been derived. Photoexcited in solution, hexafluorobenzene is capable of cycloaddition with a variety of unsaturated molecules. Like the Dewar benzene, resulting adducts have served as intermediates en route to many new fluorocarbons and fluorocarbon derivatives.

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Valence isomerization equilibria of highly fluorinated cycloocta-1,3,5-trienes

Cited by 14 publications

References 0 publications

Novel Keto−Enol Systems: Cyclobutane Derivatives

Novel Keto−Enol Systems: Cyclobutane Derivatives

Effect of Fluorine Substitution on the Energies of Small Ring Compounds

Hexafluorobenzene Photochemistry: Wellspring of Fluorocarbon Structures

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