Photolysis of benzene vapor. Benzvalene formation at wavelengths 2537-2370 A

Kaplan, Louis; Wilzbach, K. E.

doi:10.1021/ja01014a086

Cited by 100 publications

(44 citation statements)

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“…Cyclobutadiene, cyclopentadienone, pentalene, and other cyclic, π-conjugated compounds, with formal [4n] ring π-electrons, easily dimerize to get rid of antiaromaticity. Upon irradiation, benzene rather isomerize to fulvene and the very strained benzvalene than stay [4n + 2] π-electron antiaromatic (49). We show here that many organic compounds that undergo ESPT are antiaromatic at their first ππ* states-and proton transfer provides the perfect escape route.…”

Section: Discussionmentioning

confidence: 80%

Excited-state proton transfer relieves antiaromaticity in molecules

Karas

Ottosson

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Baird’s rule explains why and when excited-state proton transfer (ESPT) reactions happen in organic compounds. Bifunctional compounds that are [4n + 2] π-aromatic in the ground state, become [4n + 2] π-antiaromatic in the first 1ππ* states, and proton transfer (either inter- or intramolecularly) helps relieve excited-state antiaromaticity. Computed nucleus-independent chemical shifts (NICS) for several ESPT examples (including excited-state intramolecular proton transfers (ESIPT), biprotonic transfers, dynamic catalyzed transfers, and proton relay transfers) document the important role of excited-state antiaromaticity. o-Salicylic acid undergoes ESPT only in the “antiaromatic” S1 (1ππ*) state, but not in the “aromatic” S2 (1ππ*) state. Stokes’ shifts of structurally related compounds [e.g., derivatives of 2-(2-hydroxyphenyl)benzoxazole and hydrogen-bonded complexes of 2-aminopyridine with protic substrates] vary depending on the antiaromaticity of the photoinduced tautomers. Remarkably, Baird’s rule predicts the effect of light on hydrogen bond strengths; hydrogen bonds that enhance (and reduce) excited-state antiaromaticity in compounds become weakened (and strengthened) upon photoexcitation.

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Section: Discussionmentioning

confidence: 80%

Excited-state proton transfer relieves antiaromaticity in molecules

Karas

Ottosson

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…The quantum yield of photochemical products from the channel 3 decay is very small (∼0.02), 37 pathway can be important for benzotriazoles since, as we have seen above the proton transfer decay pathway is essentially 100% efficient at regeneration of the ground-state enol species (due to the lack of a stable keto minimum on the ground state). Benzotriazoles do however show some degradation on very long time scales.…”

Section: Resultsmentioning

confidence: 93%

Theoretical Study of Benzotriazole UV Photostability: Ultrafast Deactivation through Coupled Proton and Electron Transfer Triggered by a Charge-Transfer State

et al. 2004

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A theoretical CASSCF study of the reaction path for excited-state intramolecular proton transfer (ESIPT) for a model system derived from the UV absorber 2-(2'-hydroxyphenyl) benzotriazole without the fused benzo ring on the triazole has been carried out. A planar reaction path can be optimized but is shown to have no physical significance. The true reaction path involves twisted geometries. Adiabatic proton transfer is triggered by a charge-transfer from the phenol to the triazole group, and is followed by radiationless decay at the keto form. Along the nonplanar reaction path, there is a coupled proton and electron transfer in a manner similar to tryptophan. This rationalizes unexpected experimental results on the effect of electron withdrawing substituent groups on the photostability. The coupled proton and electron transfer is followed by a barrierless relaxation in the ground state to recover the enol form. An alternative photostabilization pathway from a phenyl localized state has also been documented and is similar to the channel 3 decay pathway in benzene photochemistry. Additionally, a long-lived intermediate for a twisted intramolecular charge-transfer (TICT) state has been identified as the species potentially responsible for the increase of blue fluorescence in strongly polar media.

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“…39 Theoretical study of the gasphase proton affinity of phosphabenzene has been reported using ab initio SCF calculations. 40 The results of ab initio study of valence isomers of phosphabenzene (see Scheme 3) are shown in Tables IV and V. According to these calculations, 3-phosphabenzvalene (17) is 43.29 kcal mol −1 less stable than the planar 6π-electron phosphabenzene (8). Other valence isomers derived from benzvalene (2), namely 2-phospha-and 3-phospha-benzvalene, are 6.57 and 15.55 kcal mol −1 less stable than (17).…”

Section: ) Of Phosphabenzene (8) Andmentioning

confidence: 95%

An Ab Initio Molecular Orbital Study of Valence Bond Isomers of Silabenzene and Phosphabenzene

Yavari

Dehghan

Nikpoor-Nezhati

2003

Phosphorus, Sulfur, and Silicon and the Related Elements

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6-31G * for a single point total energy calculation are reported for silabenzene (7), phosphabenzene (8) and 16 valence bond isomers of silabenzene and phosphabenzene (9-24). The calculated energy difference (19.78 kcal mol −1 ) between silabenzene and the most stable valence bond isomer of silabenzene (1-silabenzvalene, 9) is much smaller than the difference (73.60 kcal mol −1 ) between benzene and benzvalene (2). The energy difference between phosphabenzene and the most stable valence bond isomer of phosphabenzene (1-phosphabenzvalene, 17) is calculated to be 43.29 kcal mol −1 .

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Photolysis of benzene vapor. Benzvalene formation at wavelengths 2537-2370 A

Cited by 100 publications

References 0 publications

Excited-state proton transfer relieves antiaromaticity in molecules

Excited-state proton transfer relieves antiaromaticity in molecules

Theoretical Study of Benzotriazole UV Photostability: Ultrafast Deactivation through Coupled Proton and Electron Transfer Triggered by a Charge-Transfer State

An Ab Initio Molecular Orbital Study of Valence Bond Isomers of Silabenzene and Phosphabenzene

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