The Puzzle of Bond Length Variation in Substituted Cyclobutenes. A New Example: Molecular Structure and Conformations of 1,2-Dimethoxy-3,3,4,4-tetrafluorocyclobut-1-ene

Richardson, Alan D.; Hedberg, Kenneth; Lunelli, Bruno

doi:10.1021/jp911185z

Cited by 5 publications

(6 citation statements)

References 18 publications

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“…The calculated C–C bond lengths for the cyclobutene ring in trans- 25 of 1.583, 1.522, 1.520, and 1.340 Å for C3–C4, C1–C3, C2–C4, and C1–C2, respectively, are a good match for a strained cyclobutene ring. Elongation of the C3–C4 bond has been observed previously in substituted cyclobutenes. , The outward ring-opening transition structure TS3 differs markedly from the inward ring-opening structure TS4 . Starting from trans- 25 , ring opening to form ( E , E )-diene 29 via TS3 results in significant elongation of the cyclobutene CC bond (1.397 Å) and shortening of the C sp 2 –C sp 3 bonds (1.416 and 1.415 Å) in the transition structure.…”

Section: Resultssupporting

confidence: 58%

“…Elongation of the C3−C4 bond has been observed previously in substituted cyclobutenes. 56,57 The outward ring-opening transition structure TS3 differs markedly from the inward ring-opening structure TS4. Starting from trans-25, ring opening to form (E,E)-diene 29 via TS3 results in significant elongation of the cyclobutene CC bond (1.397 Å) and shortening of the C sp 2 −C sp 3 bonds (1.416 and 1.415 Å) in the transition structure.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Using Ring Strain to Control 4π-Electrocyclization Reactions: Torquoselectivity in Ring Closing of Medium-Ring Dienes and Ring Opening of Bicyclic Cyclobutenes

et al. 2017

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Syntheses of strained cyclic dienes were accomplished via palladium(II)-catalyzed oxidative cyclizations of terminal bis(vinylboronate esters). The reactions generate strained (E,E)-1,3-dienes that undergo spontaneous 4π-electrocyclizations to form bicyclic cyclobutenes. Formation of the cyclobutenes is driven by the strain in the medium-ring (E,E)-1,3-diene intermediate. Thermal ring openings of the cyclobutenes give (Z,Z)-1,3-diene products, again for thermodynamic reasons. DFT calculations verified the thermodynamic versus kinetic control of the reactions, and kinetic studies are in excellent agreement with the calculated energy changes. An extension of the tandem coupling/4π-electrocyclization pathway was demonstrated by a palladium(II)-catalyzed oxidative homocoupling/8π-electrocyclization cascade.

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Section: Resultssupporting

confidence: 58%

Section: ■ Results and Discussionmentioning

confidence: 99%

Using Ring Strain to Control 4π-Electrocyclization Reactions: Torquoselectivity in Ring Closing of Medium-Ring Dienes and Ring Opening of Bicyclic Cyclobutenes

et al. 2017

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“…During the last two decades several experimental and theoretical studies have been carried out both on the same perfluorinated compound and on other CB derivatives, with various degrees of fluorination, ,− or even bearing different functional groups. , In our combined experimental/theoretical analysis of hexafluorocyclobutene by means of accurate single-crystal X-ray diffraction and periodic optimizations in the solid state, we found values for the Csp 3 –Csp 3 bond very close (or even identical, in terms of our X-ray estimated standard deviations, esd’s) to both the MW outcomes for CB and the last results of Császár. This author has proposed to rationalize his findings in terms of a simple rehybridization model, “namely that the increased number of fluorines attached to a carbon atom increases the s character of the carbon bonds and tends to shorten all the bonds around the carbon.…”

Section: Introductionsupporting

confidence: 62%

“…Both recently and in the past, ,, the Coulomb repulsion between positively charged Csp 3 atoms has been invoked to account for the C1–C4 bond length in fluorinated CB derivatives. This rationalization appears to be in contrast with the topological analysis (see sections and ), as the latter shows a strengthening of the bonds linking the substituted carbon atoms upon fluorine substitution at both allylic and vinylic positions, even if the carbon charges increase enormously (from ≈0 e up to ≈ +1.2 e at allylic positions) when hydrogen is replaced by fluorine.…”

Section: Resultsmentioning

confidence: 99%

Rationalizing the Effect of Halogenation on the Molecular Structure of Simple Cyclobutene Derivatives by Topological Real-Space Analysis of Their Electron Density

et al. 2011

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The accurate gas-phase equilibrium structures on the ground-state potential energy surface of the complete series of fluorinated and chlorinated cyclobutene derivatives with C(2v) symmetry have been evaluated at DFT PBE0/6-311++G(d,p) theory level. The optimized geometries have been compared with all the available experimental data reported in the literature, as obtained by microwave spectroscopy (MW) and gas-phase electron diffraction (GED) techniques. For hexafluorocyclobutene and 1,2-dichloro-3,3',4,4'-tetrafluorocyclobut-1-ene, the results of accurate low-temperature single-crystal X-ray diffraction experiments have also been considered. Structural changes within the cyclobutene ring, as induced by fluorination and chlorination at allylic and vinylic positions, have been correlated with changes in the corresponding theoretical charge densities. To this aim, several local and nonlocal topological descriptors provided by the quantum theory of atoms in molecules, QTAIM, have been employed, with particular emphasis on the delocalization indices and integrated source function decomposition schemes. Key factors for the resulting molecular structures are the chemical nature and the steric hindrance of the substituents, as well as quantum-mechanical effects, such as delocalization and partial conjugation. When fluorine atoms replace hydrogens at allylic or vinylic positions, the corresponding Csp(3)-Csp(3) or Csp(2)═Csp(2) bonds between the substituted carbons undergo a significant strengthening, while chlorination has just the opposite effect. In the latter case the steric hindrance between bulky chlorine atoms occupying vicinal positions is crucial in determining the single Csp(3)-Csp(3) bond length. These findings are discussed in the context of the reactivity of chemically related chlorofluorocarbon compounds.

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“… a B3LYP/cc-pVTZ. b Reference . c Reference . d Reference . e This work; the values are weighted averages. f Reference . …”

Section: Discussionmentioning

confidence: 99%

Molecular Structure and Conformations of 1,2-Dimethoxycyclobutene-3,4-dione. An Electron-Diffraction Investigation Augmented by Quantum Mechanical and Normal Coordinate Calculations

Costello

Hedberg

2014

J. Phys. Chem. A

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The structure and conformations of 1,2-dimethoxycyclobutene-3,4-dione in the vapor at a temperature of 185 °C have been measured by gas-phase electron diffraction. The molecule exists in two forms, one of symmetry C2v with the methyl groups trans to the double bond, and one of Cs symmetry with a methyl group cis and the other trans to this bond (these forms hereafter designated as trans and cis). The molar ratio trans/cis is 68/32 with a 2σ uncertainty of about 24. Many of the parameter values for the two forms are very nearly alike and could not be measured experimentally. With the adoption of parameter differences calculated at the B3LYP/cc-pVTZ level, the following bond distances (r(g)/Å) and bond angles (∠/deg) with estimated 2σ uncertainties were obtained for trans/cis: C1═C2 = 1.381(9)/1.381, C1-C4 = 1.493(11)/1.495, C3-C4 = 1.543(20)/1.545, C═O = 1.203(4)/⟨1.200⟩, C1-O = 1.316(6)/⟨1.320⟩, O-CH3 = 1.444(9)/⟨1.443⟩, C═C-C3 = 93.1(5)/⟨93.1⟩, C3-C4═O = 136.7(29)/⟨136.9⟩, C═C-O = 131.0(23)/137.5, and 131.8, C-O-C = 117.2(12)/118.2 and 116.9; the individual angle values for the cis form listed as averages differ very little. The bond distances and bond angles are in excellent qualitative agreement with prediction based on conventional ideas about the effects of conjugation and hybridization, and their relative values agree very well with predictions from quantum mechanical calculations.

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The Puzzle of Bond Length Variation in Substituted Cyclobutenes. A New Example: Molecular Structure and Conformations of 1,2-Dimethoxy-3,3,4,4-tetrafluorocyclobut-1-ene

Cited by 5 publications

References 18 publications

Using Ring Strain to Control 4π-Electrocyclization Reactions: Torquoselectivity in Ring Closing of Medium-Ring Dienes and Ring Opening of Bicyclic Cyclobutenes

Using Ring Strain to Control 4π-Electrocyclization Reactions: Torquoselectivity in Ring Closing of Medium-Ring Dienes and Ring Opening of Bicyclic Cyclobutenes

Rationalizing the Effect of Halogenation on the Molecular Structure of Simple Cyclobutene Derivatives by Topological Real-Space Analysis of Their Electron Density

Molecular Structure and Conformations of 1,2-Dimethoxycyclobutene-3,4-dione. An Electron-Diffraction Investigation Augmented by Quantum Mechanical and Normal Coordinate Calculations

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