Energy storage and release. Direct and sensitized photoreactions of benzvalene. Evidence for a quantum chain process, an adiabatic photorearrangement, a degenerate photovalence isomerization, and two reactive triplet states

Renner, Carl A.; Katz, Thomas J.; Pouliquen, Joseph; Turro, Nicholas J.; Waddell, Walter H.

doi:10.1021/ja00842a059

Cited by 35 publications

(15 citation statements)

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“…This prediction should be most reliable in those cases where the hyperconjugative effects are particularly strong, e.g., in the case of 1-3. The observed photochemical rearrangement of 1 to benzene [23] is consistent with our prediction. It is also interesting that methoxy-azulvalene has been found to undergo clean isomerization to methoxy-azulene on irradiation [24], in accordance with our expectation.…”

supporting

confidence: 92%

Electronic States of Phenylene and Naphthylene Bicyclobutanes. Linear Dichroism in Stretched Polyethylene

Spanget‐Larsen

Gubernator

Gleiter

et al. 1983

Helvetica Chimica Acta

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SummaryExcited singlet states of bicyclobutylene-benzene (2), 1,2 : 4,5-bis (bicyclobuty1ene)benzene (3), 2,3-bicyclobutylene-naphthalene (4), and 1,8-bicyclobutylene-naphthalene (5) are investigated by means of linear dichroic absorption spectroscopy of molecules oriented in stretched polyethylene films and by semiempirical model calculations. The results indicate a strong hyperconjugative impact of the bicyclobutylene group on the aromatic chromophores in these compounds. Valence isomerization to aromatic products is predicted as the preferred photochemical pathway.

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supporting

confidence: 92%

Electronic States of Phenylene and Naphthylene Bicyclobutanes. Linear Dichroism in Stretched Polyethylene

Spanget‐Larsen

Gubernator

Gleiter

et al. 1983

Helvetica Chimica Acta

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“…All three methods gave the same result, but because of the increased dispersion, the 13 C NMR spectra provide the clearest proof of the pathway-(s) occurring. As shown in Figure 6a, a 13 C NMR spectrum of a mixture of the three isomers (41% para, 34% meta, and 25% ortho) gives 10 signals in the region that corresponds to the aromatic carbons which are hydrogen substituted; four of these belong to the ortho isomer, four to the meta and two to the para. Of the 10, eight can be assigned on the basis of literature spectra, 32 but the choice of assignment of C5 and C6 for the signals labeled 2 and 3 in Figure 6a at δ 128.9 and 129.2 for MMBN is not known and proved to be inconsequential.…”

Section: Resultsmentioning

confidence: 72%

Section: Resultsmentioning

confidence: 99%

“…The position of the deuterium labels in the three isomers was determined by 1 H, 2 H, or 13 C NMR spectra. All three methods gave the same result, but because of the increased dispersion, the 13 C NMR spectra provide the clearest proof of the pathway-(s) occurring. As shown in Figure 6a, a 13 C NMR spectrum of a mixture of the three isomers (41% para, 34% meta, and 25% ortho) gives 10 signals in the region that corresponds to the aromatic carbons which are hydrogen substituted; four of these belong to the ortho isomer, four to the meta and two to the para.…”

Section: Resultsmentioning

confidence: 99%

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Photochemical Equilibration/Isomerization of p-, m-, and o-Methylbenzonitrile

MacLeod

Pincock

et al. 1998

J. Am. Chem. Soc.

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The phototransposition reactions in acetonitrile of p-, m-, and o-methylbenzonitrile have been studied. Any one of the three is converted to the other two by either a 1,2-or 1,3-isomerization in a primary photochemical step. However, the reactivities are quite different with the relative values for para:meta:ortho ) 32:4:1. For both the para and meta isomers, extended irradiations approach a calculated steady-state composition of para:meta:ortho ) 3:20:77. Quenching of the excited triplet state of the para and meta isomers with 2,4-dimethyl-1,3-butadiene indicates that these reactions are occurring from the excited singlet state. Irradiation of selectively labeled 2,6-dideuterio-4-methylbenzonitrile demonstrates that only the cyano-substituted carbon undergoes migration.

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“…Finally, one can ask why is the quantum yield for the photoreaction not higher than 0.045? Experiments reveal that a photostationary state evolves in a solution with both benzene and benzvalene present. Furthermore, earlier experiments give E (T 1 ; benzene) = 84.1 kcal/mol and E (T 1 ; benzvalene) ≈ 65 kcal/mol, while our (U)B3LYP/6-311+G(d,p) computations give E (T 1 ) for the two compounds at 83.5 and 60.3 kcal/mol, respectively. Also, the calculated energy needed to reach the vertically excited T 1 state of benzvalene (79.3 kcal/mol) is slightly lower than the triplet energy of benzene (83.5 kcal/mol).…”

Section: Results and Discussionmentioning

confidence: 99%

Impact of Excited-State Antiaromaticity Relief in a Fundamental Benzene Photoreaction Leading to Substituted Bicyclo[3.1.0]hexenes

et al. 2020

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Benzene exhibits a rich photochemistry which can provide access to complex molecular scaffolds that are difficult to access with reactions in the electronic ground state. While benzene is aromatic in its ground state, it is antiaromatic in its lowest ππ* excited states. Herein, we clarify to what extent relief of excited-state antiaromaticity (ESAA) triggers a fundamental benzene photoreaction: the photoinitiated nucleophilic addition of solvent to benzene in acidic media leading to substituted bicyclo[3.1.0]hex-2-enes. The reaction scope was probed experimentally, and it was found that silyl-substituted benzenes provide the most rapid access to bicyclo[3.1.0]hexene derivatives, formed as single isomers with three stereogenic centers in yields up to 75% in one step. Two major mechanism hypotheses, both involving ESAA relief, were explored through quantum chemical calculations and experiments. The first mechanism involves protonation of excited-state benzene and subsequent rearrangement to bicyclo[3.1.0]hexenium cation, trapped by a nucleophile, while the second involves photorearrangement of benzene to benzvalene followed by protonation and nucleophilic addition. Our studies reveal that the second mechanism is operative. We also clarify that similar ESAA relief leads to puckering of S 1 -state silabenzene and pyridinium ion, where the photorearrangement of the latter is of established synthetic utility. Finally, we identified causes for the limitations of the reaction, information that should be valuable in explorations of similar photoreactions. Taken together, we reveal how the ESAA in benzene and 6π-electron heterocycles trigger photochemical distortions that provide access to complex three-dimensional molecular scaffolds from simple reactants.

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Energy storage and release. Direct and sensitized photoreactions of benzvalene. Evidence for a quantum chain process, an adiabatic photorearrangement, a degenerate photovalence isomerization, and two reactive triplet states

Cited by 35 publications

References 1 publication

Electronic States of Phenylene and Naphthylene Bicyclobutanes. Linear Dichroism in Stretched Polyethylene

Electronic States of Phenylene and Naphthylene Bicyclobutanes. Linear Dichroism in Stretched Polyethylene

Photochemical Equilibration/Isomerization of p-, m-, and o-Methylbenzonitrile

Impact of Excited-State Antiaromaticity Relief in a Fundamental Benzene Photoreaction Leading to Substituted Bicyclo[3.1.0]hexenes

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