Observation of benzocyclobutadiene by flow nuclear magnetic resonance

Trahanovsky, Walter S.; Fischer, David

doi:10.1021/ja00168a059

Cited by 36 publications

(42 citation statements)

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“…Benzocyclobutadiene (43) may become aromatic by inserting the function values of «R G (i)« and «R Gr (i)« for the bond-alternating variant into eqs 2426. 75 This semibenzenoid hydrocarbon, however, is still extremely reactive and has been trapped in an argon matrix at 20 K. 76 …”

Section: Visualization Of Aromatic Stabilizationmentioning

confidence: 99%

“…31 Triangular (73) and azulenoid (77) isomers of 71 likewise exhibit very small SSE(MC) values, so do [10]coronaphene (74) and [9]coronaphene (75). No macrocyclic conjugation circuits can be chosen from septulene (72) and hexa-m-phenylene (76). This must be why SSE(MC) values for these molecules are vanishingly small.…”

Section: Superaromatic Stabilization Energy For Macrocyclesmentioning

confidence: 99%

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Graph Theory of Aromatic Stabilization

Aihara¹

2016

BCSJ

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Aromaticity is very sensitive to the geometry of the π-system. Topological resonance energy (TRE), defined graphtheoretically, represents an aromatic stabilization energy (ASE) arising from cyclic conjugation in the π-system. TRE can be calculated for not only ground-state but also excited-state species. The TRE concept has since been extended analytically to solve many different problems concerning aromaticity and reactivity. Bond resonance energy (BRE), defined in harmony with TRE, is an excellent probe for exploring kinetic stability of cyclic π-systems. It represents the contribution of individual π-bonds to global aromaticity. The well-known isolated pentagon rule (IPR) for fullerenes was verified in terms of BRE. Superaromatic stabilization energy (SSE) defined for macrocyclic π-systems finally confirmed the absence of macrocyclic aromaticity in kekulene. A novel local aromaticity index for polycyclic aromatic hydrocarbons (PAHs) was devised by reinterpreting the definition of SSE. We then found that aromatic properties of some PAHs are not compatible with Clar's aromatic sextet rule. We now feel that many fundamental problems with regard to aromatic stabilization and related phenomena have been solved conceptually.

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Section: Visualization Of Aromatic Stabilizationmentioning

confidence: 99%

Section: Superaromatic Stabilization Energy For Macrocyclesmentioning

confidence: 99%

Graph Theory of Aromatic Stabilization

Aihara¹

2016

BCSJ

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“…evaluated the aromatic character in the central six‐membered rings (6MRs) of 4 , 5 and 6 (Figure b), and found that the “benzene‐like” 6MR in 4 is aromatic whereas the “[6]radialene‐like” ones in 5 and 6 are non‐aromatic . In addition, the research for benzocyclobutadiene and the exploration of the origin of the aromaticity of benzene ring in benzocyclobutadiene have been studied by both experimental and theoretical chemists . The prevailing view supported that the benzene ring in benzocyclobutadiene is essentially nonaromatic.…”

Section: Introductionmentioning

confidence: 99%

“…[20] In addition, the research for benzocyclobutadiene and the exploration of the origin of the aromaticity of benzene ring in benzocyclobutadieneh ave been studied by both experimentala nd theoretical chemists. [21][22][23][24][25] The prevailing view supported that the benzene ring in benzocyclobutadiene is essentially nonaromatic. Our ongoing interest in aromaticity [26][27][28][29] has led us to probe ap ossibility to achievea na ntiaromatic benzene ring.…”

Section: Introductionmentioning

confidence: 99%

Predicting an Antiaromatic Benzene Ring in the Ground State Caused by Hyperconjugation

Zhao

Xie

Sun

et al. 2019

Chemistry An Asian Journal

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Benzene, the prototype of aromatics, has six equivalent C−C bonds (1.397 Å), which are intermediate between a C−C double bond and a C−C single bond. For over 80 years, chemists have spent much effort on freezing a localized structure to obtain a distorted bond‐length alternating benzene ring in the ground state, leading to various localized trisannelated benzene rings. However, most of the central benzene rings are still aromatic or nonaromatic. Here we report an antiaromatic benzene ring caused by hyperconjugation. Specifically, symmetric annulation of 5,5‐difluorocyclopentadiene results in an antiaromatic benzene ring, which is supported by various aromaticity indices, including nucleus‐independent chemical shift, anisotropy of the induced current density, π‐separated electron‐localization function and heat of hydrogenation. Our findings highlight a strong power of hyperconjugation, a “weak” interaction in organic chemistry, paving the way for designing and realizing more novel (anti)aromatics.

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“…molecule with a diatropic ring current; 1c a cyclobutadiene contributor to this electronic structure would be a high-energy diradical or diionic structure (Fig. 9), (2) NMR NICS calculations show the four-membered ring to be opposite in aromatic character to that in benzocyclobutadiene, 1b which latter has a typically reactive antiaromatic cyclobutadiene ring, 33 and (3) cyclobutadiene has high diradical character and a small singlet−triplet gap, 34 while benzene, with no diradical character, has a large singlet−triplet gap. 35 Table 4 shows the calculated singlet−triplet gaps for cyclobutadiene, benzene, and bowtiene (the singlets are the ground states).…”

Section: Moleculementioning

confidence: 99%

The chemistry of bowtiene (tricyclo[5.3.0.0^2,6]decapentaene): a computational study

LewarsErrol

2014

Can. J. Chem.

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Reactions of bowtiene (tricyclo[5.3.0.0 2,6 ]decapentaene, cyclobuta [1,2:3,4]dicyclopentene, bicyclopentadienylene, a tricyclic analogue of [10]annulene), in the sphere of unimolecular decomposition and dimerization were studied computationally to gauge its stability and reactivity, which are relevant to its feasability as a synthetic goal. The intuitively likeliest rearrangement mode to give species of lower energy begins with rearrangement to the 1,5-dehydronaphthalene diradical; this was calculated to have a barrier of approximately 220 kJ mol −1 , too high for reaction at room temperature. Nevertheless, the energetics of rearrangement of the 1,5-diradical to the monocyclic 1,6-didehydro[10]annulene, a species of interest regarding its relationship to bowtiene and the diradical, were studied. The energy of bowtiene was compared with that of several other tricyclic 10 C 10 H 6 cyclic polyenes. Résumé :Réactions du bowtiene (tricyclo[5.3.0.0 2,6 ]décapentaene, cyclobuta[1,2:3,4]dicyclopentène, bicyclopentadienylène, analogue tricyclique du [10]annulène), dans le cadre d'une décomposition unimoléculaire et d'une dimérisation, ont été étudiées par des calculs afin de mesurer la stabilité et la réactivité de ce composé, qui sont liés à l'objectif visé de la faisabilité d'une synthèse. Le mode de réarrangement instinctivement le plus susceptible de générer des espèces de plus basse énergie commence est d'abord le réarrangement sous forme du diradical 1,5-déhydronaphthalène; les calculs ont montré que la barrière de ce réarrangement était d'environ 220 kJ mol −1 , une valeur trop élevée pour permettre une réaction à la température ambiante. Cependant, le profil énergétique du réarrangement du 1,5-diradical sous forme de 1,6-didéhydro[10]annulène monocyclique, une espèce intéressante du point de vue de son lien avec le bowtiene et le diradical, a été étudié. L'énergie du bowtiene a été comparée avec celle des plusieurs autres polyènes 10 C 10 H 6 tricycliques. [Traduit par la Rédaction] Mots-clés : bowtiene, tricyclo[5.3.0.0 2,6 ]décapentaene, calculs de théorie de la fonctionnelle de la densité (DFT), stabilité, rearrangement.

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Observation of benzocyclobutadiene by flow nuclear magnetic resonance

Cited by 36 publications

References 0 publications

Graph Theory of Aromatic Stabilization

Graph Theory of Aromatic Stabilization

Predicting an Antiaromatic Benzene Ring in the Ground State Caused by Hyperconjugation

The chemistry of bowtiene (tricyclo[5.3.0.0^2,6]decapentaene): a computational study

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Observation of benzocyclobutadiene by flow nuclear magnetic resonance

Cited by 36 publications

References 0 publications

Graph Theory of Aromatic Stabilization

Graph Theory of Aromatic Stabilization

Predicting an Antiaromatic Benzene Ring in the Ground State Caused by Hyperconjugation

The chemistry of bowtiene (tricyclo[5.3.0.02,6]decapentaene): a computational study

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The chemistry of bowtiene (tricyclo[5.3.0.0^2,6]decapentaene): a computational study