The Structures of 1<i>H</i>‐Cyclopropabenzene and Its 1,1‐Bis(triisopropylsilyl) Derivative

Neidlein, R.; Christen, Detlev; Poignee, V.; Boese, Roland; Bläser, D.; Gieren, Alfred; Ruíz-Pérez, Catalina; Hübner, Thomas

doi:10.1002/anie.198802941

Cited by 51 publications

(20 citation statements)

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“…Fully optimized MP2(fc)/6-31+G(d) structures for benzocyclopropene ( 5H ), benzocyclopropenyl anion ( 5 ), and the latters inversion transition state ( 5pl ) were computed, and the most important geometrical data are summarized in Table and is in reasonable agreement with the experimental X-ray data, although the C−C bonds are systematically too long by approximately 0.004 and 0.02 Å, respectively. Apparently, the diffuse sp functions, which are needed to adequately describe the geometry of anions, lead to a slightly poorer structure in this instance.…”

Section: Resultsmentioning

confidence: 63%

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Benzocyclopropenyl Anion: A Stable 8π-Electron Species

et al. 1997

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The conjugate base of benzocyclopropene has been generated in the gas phase. Its reactivity and thermodynamic stability were explored. The measured acidity is DeltaH degrees (acid)(benzocyclopropene) = 386 +/- 3 kcal/mol, and the electron affinity of benzocyclopropenyl radical is 0.51 eV < EA < 1.11 eV. Ab initio calculations satisfactorily reproduce the experimental results and provide additional insights. Benzocyclopropene is found to be 34.5 kcal/mol more acidic than the allylic position of cyclopropene and only 4 +/- 3 kcal/mol less acidic than toluene. These findings are explained in terms of the structure and electronic properties of benzocyclopropenyl anion.

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Section: Resultsmentioning

confidence: 63%

“… a All distances are in angstroms and angles in degrees. X-ray crystal data are given in parentheses and are taken from ref . …”

Section: Methodsmentioning

confidence: 99%

Benzocyclopropenyl Anion: A Stable 8π-Electron Species

et al. 1997

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“…The deformation of the benzene moiety in 10 has been discussed in terms of the Mills−Nixon effect . The MP2/6-31G* geometry (Figure ) readily reproduces the X-ray structure of 10 , with the calculated bond lengths uniformly longer by ∼0.02 Å. The annelated C−C bond and the adjacent bonds are shortened while the rest of the C−C bonds are elongated.…”

Section: Discussionmentioning

confidence: 91%

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C₇H₆ Energy Surface

1996

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Ab initio calculations at the G2(MP2,SVP) and B-LYP/6-311+G(3df,2p)+ZPVE levels have been used to examine the potential energy surface of C(7)H(6). Fulvenallene (6) is the most stable C(7)H(6) isomer considered in this study. 1-Ethynylcyclopentadiene (9A), benzocyclopropene (10), and 1,2,4,6-cycloheptatetraene (4) lie 12, 29, and 49 kJ mol(-)(1), respectively, above 6. Phenylcarbene (1) is calculated is to have a triplet ((3)A") ground state, 16 kJ mol(-)(1) more stable than the singlet state ((1)A'). Interconversion of 1 and 4 is predicted to have a moderate activation barrier, with the involvement of a stable bicyclic intermediate (bicyclo[4.1.0]hepta-2,4,6-triene, 2). However, 2 is found to lie in a shallow potential energy well with a small barrier (8 kJ mol(-)(1)) to rearrangement to 4. At the G2(RMP2,SVP)//QCI level, the (3)A(2) and (3)B(1) triplet states of cycloheptatrienylidene ((3)3) are predicted to lie very close in energy. The singlet "aromatic" cycloheptatrienylidene ((1)3, (1)A(1)) is found to be a transition structure interconverting two chiral cyclic allenes (4) and it lies approximately 25 kJ mol(-)(1) below the triplet states. Bicyclo[3.2.0]hepta-1,3,6-triene (5) is predicted to be a stable equilibrium structure, lying in a significant energy well. Rearrangement of 4 to 5 constitutes the rate-determining step for the rearrangement of phenylcarbene to fulvenallene (6), the ethynylcyclopentadienes (9), and spiro[2.4]heptatriene (7). Rearrangement of 9A to 6, via a 1,4-H shift, requires a large barrier of 325 kJ mol(-)(1). Rearrangement of benzocyclopropene (10) to 6 involves a methylenecyclohexadienylidene intermediate (27) and is associated with an energy barrier of 223 kJ mol(-)(1). The calculated mechanisms and energetics for the interconversions of various C(7)H(6) isomers are in good accord with experimental results to date.

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“…This postulate states that annelation of small rings onto benzene induces significant alternation of bond lengths of the six-membered ring because of strain associated with bond angle deformation. This concept, which was proposed when benzene was thought by many to be an equilibrating mixture of valence tautomers, has generally been dismissed on the basis of more recent experimental and computational work, however [18][19][20]. Fowler et al have computed ring current densities of benzene fused with several small-ring hydrocarbons, and have shown that fusion of benzene with one or more cyclobutadiene rings disrupts the benzene ring current, but no disruption in the benzene ring current is observed when only saturated small rings are fused [21].…”

Section: Introductionmentioning

confidence: 99%

Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons

Martin¹,

Teague²,

Mills³

2010

Symmetry

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Through-space isotropic NMR shielding values of a perpendicular diatomic hydrogen probe moved in a 0.5 Å grid 2.5 Å above several polycyclic aromatic/antiaromatic ring and aromatic/aromatic hydrocarbons were computed with Gaussian 03 at the GIAO HF/6-31G(d,p) level. Combinations of benzene fused with cyclobutadiene, with the tropylium ion, and with the cyclopentadienyl anion were investigated. Subtraction of the isolated H 2 isotropic value gave shielding increments (∆σ), which, when plotted against Cartesian coordinates of the probe over each hydrocarbon, gave representations of threedimensional isotropic shielding increment surfaces. The results are related to the degree of bond length alternation, the extent of π electron delocalization, and (for the ions) the NPA charge distribution. The shielding increment data are compared to NICS(1) values computed at the same level; both indicate the degree of aromaticity or antiaromaticity of the component rings.

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The Structures of 1H‐Cyclopropabenzene and Its 1,1‐Bis(triisopropylsilyl) Derivative

Cited by 51 publications

References 24 publications

Benzocyclopropenyl Anion: A Stable 8π-Electron Species

Benzocyclopropenyl Anion: A Stable 8π-Electron Species

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C₇H₆ Energy Surface

Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons

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The Structures of 1H‐Cyclopropabenzene and Its 1,1‐Bis(triisopropylsilyl) Derivative

Cited by 51 publications

References 24 publications

Benzocyclopropenyl Anion: A Stable 8π-Electron Species

Benzocyclopropenyl Anion: A Stable 8π-Electron Species

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C7H6 Energy Surface

Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons

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Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C₇H₆ Energy Surface