Does π−σ−π Through-Bond Coupling Significantly Increase C−C Bond Lengths?

Battersby, a Thomas R.; VernonClark, aand Russell; Siegel, A.

doi:10.1021/ja9622315

Cited by 52 publications

(5 citation statements)

References 56 publications

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“…The contrasting cyclization behavior of p -QDM versus TCNQ and TEQ reflects the additional steric strain in the cyclodimers of these substituted compounds, 20 and 21 , respectively. Figure shows the optimized geometries of the respective cyclodimers where, for example, the (sp 3 )C–C(sp 3 ) bond is considerably longer (1.7 Å versus 1.6 Å) in the substituted derivatives. , While compounds with even longer C–C bonds are known, compounds 20 and 21 are likely to be less kinetically stable since they carry not one but two such bonds, and they also lack the structural features to hold these long bonds together . Noncovalent interaction (NCI) analyses of the cyclodimers (Figure ) reveal additional repulsive interactions involving the cyano (TCNQ) and ethynyl (TEQ) substituents.…”

Section: Resultsmentioning

confidence: 99%

Computational and Experimental Confirmation of the Diradical Character of para-Quinonedimethide

et al. 2023

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The ground-state structure of the parent para-quinonedimethide (p-QDM) molecule is generally represented in its closed shell form, i.e., as a cyclic, nonaromatic, through-conjugated/cross-conjugated hybrid comprising four CC bonds. Nonetheless, p-QDM has been theorized to contain a contribution from its open-shell aromatic singlet diradical form. VBSCF calculations identify an open-shell contribution of 29% to the structure, while CASPT2(16,16)/def2-TZVP and ωB97XD/aug-cc-pVTZ calculations predict that dimerization proceeds along an open-shell singlet diradical pathway with a low (77 kJ/mol) barrier toward dimerization, which occurs by way of C–C bond formation between the exocyclic methylene carbons. A similar low (98 kJ/mol) barrier exists toward the reaction between a p-QDM molecule and the radical trap TEMPO. These predictions are verified experimentally through the isolation of bis-TEMPO-trapped p-QDM, its C–C coupled dimer, and by demonstrating that a mixture of p-QDM and TEMPO can initiate the radical polymerization of n-butyl acrylate at ambient temperature. In contrast to p-QDM, tetracyanoquinone (TCNQ) neither dimerizes nor reacts with TEMPO, despite having a similar diradical character to p-QDM. This lack of reactivity is consistent with both a higher kinetic barrier and a thermodynamically unfavorable process, which is ascribed to destabilizing steric clashes and polar effects.

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Section: Resultsmentioning

confidence: 99%

Computational and Experimental Confirmation of the Diradical Character of para-Quinonedimethide

et al. 2023

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“…Thus the role of indirect interaction through the ethylene bridges is negligible or merely absent, which is in agreement with ref. 36.…”

Section: Electron Density Distribution and Its Topologymentioning

confidence: 99%

The Transannular Interaction in [2.2]Paracyclophane: Repulsive or Attractive?

2003

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The molecular structure and charge density distribution in the crystal of [2.2]paracyclophane derived from the high-resolution single crystal X-ray diffraction data at 100 K is reported together with ab initio calculations of this molecule. Analysis of the atomic, anisotropic displacement parameters in a "rigid-body" model approximation has revealed that the molecule is ordered in the crystal. Topological analysis of the electron density and potential-energy density-distribution functions has demonstrated that there is no "through-space" interaction between the rings in the molecule. The role of the ethylene bridges and distortion of the aromatic desks on the inter-ring interaction are discussed.

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“…However, it has been known for years that through-bond coupling can weaken the bond without changing the bond length. 38,39 Furthermore, to describe the BDE of an expanded C-C bond, the Lennard-Jones-type potential may be more appropriate than a simple linear correlation. Thus, the change in BDE with an increase in the length of pre-strained weak C-C bonds (>1.7 Å ) should Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Longest C–C Single Bond among Neutral Hydrocarbons with a Bond Length beyond 1.8 Å

Ishigaki

Shimajiri

Takeda

et al. 2018

Chem

117

109

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Compounds with an ultralong CC single bond have been successfully constructed in three steps from commercially available dihalo aromatics. The intramolecular ''core-shell strategy'' is a key tactic for stabilizing compounds with an ultralong CC bond. Using this concept could lead to an even longer CC bond (''hyper covalent bonds'' with a bond length of 1.8-2.0 Å) because the covalently bonded state and non-bonded state are seamlessly connected in terms of the interatomic distance.

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Does π−σ−π Through-Bond Coupling Significantly Increase C−C Bond Lengths?

Cited by 52 publications

References 56 publications

Computational and Experimental Confirmation of the Diradical Character of para-Quinonedimethide

Computational and Experimental Confirmation of the Diradical Character of para-Quinonedimethide

The Transannular Interaction in [2.2]Paracyclophane: Repulsive or Attractive?

Longest C–C Single Bond among Neutral Hydrocarbons with a Bond Length beyond 1.8 Å

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