An electron/proton-transfer sequence for quenching chloranil triplets by cyclopolyenes

Jones, Guilford; Haney, William A.

doi:10.1021/j100412a103

Cited by 23 publications

(12 citation statements)

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“…6), which is proposed to have a similar structure as a product that has been reported in the literature 41 . It is assumed to be formed within the geminate dimer radical pair 43 : first, the AQS* abstracts a proton from the CH 3 group at N1, followed by addition of AQSH* as indicated in Fig. 6.…”

Section: Resultsmentioning

confidence: 53%

Photo‐cidnp Study of Pyrimidine Dimer Splitting I: Reactions Involving Pyrimidine Radical Cation Intermediates

Pouwels

Kaptein

Hartman

et al. 1995

Photochem & Photobiology

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The light-induced splitting of pyrimidine dimers was studied using the electron acceptor anthraquinone-2-sulfonate (AQS) as a photosensitizer. To this end, photochemically induced dynamic nuclear polarization (photo-CIDNP) experiments were performed on a series of pyrimidine monomers and dimers. The CIDNP spectra demonstrate the existence of both the dimer radical cation, which is formed by electron transfer from the dimer to the photoexcited sensitizer AQS*, and its dissociation product, the monomer radical cation. In spectra of 1,1'-trimethylene bridged cis, syn pyrimidine dimers, polarization is observed that originates from a spin-sorting process in the dimer radical pair. This points to a relatively long lifetime of the dimer radical cation involved, which is presumably due to stabilization by the trimethylene bridge. Polarization originating from a dimer radical pair is detected in the spectrum of trans,anti (1,3-dimethyluracil) dimer as well. The spectra of the bridged pyrimidines also demonstrate the reversibility of the dissociation of dimer radical cation into monomer radical cation, which is concluded from the observation of polarization in the dimer as a result of spin sorting in the monomer radical pair.

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Section: Resultsmentioning

confidence: 53%

Photo‐cidnp Study of Pyrimidine Dimer Splitting I: Reactions Involving Pyrimidine Radical Cation Intermediates

Pouwels

Kaptein

Hartman

et al. 1995

Photochem & Photobiology

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“…Similar transient spectra were obtained upon the quenching of CX* with hexamethylbenzene and in other solvents of low polarity such as dichloromethane or carbon tetrachloride. In the case of chloranil, the protonated chloranil anion radical ( CA-H • or hydrochloranil) was observed . Hydrochloranil yields could be estimated on the basis of its extinction coefficient at 435 nm (ε 435 = 7700 M -1 cm -1 ) …”

Section: Resultsmentioning

confidence: 99%

“…For our studies on the mechanism of bimolecular electron transfer, we used excited quinones as electron acceptors and examined their diffusional interaction with the polymethylbenzene electron donors in Chart by time-resolved (ps/μs) absorption spectroscopy. Chloranil and the related 2,5-dichloroxyloquinone were chosen as transient acceptors for the following reasons: (i) Upon photoexcitation, both quinones form long-lived (μs) excited triplet states which function as powerful one-electron oxidants for a variety of aromatic donors. , (ii) For chloranil, both exciplex formation , and electron transfer to the excited state 16-18 have been established. (iii) Both quinones also form EDA complexes with arene donors in the ground state, as established by UV−vis spectroscopy…”

Section: Introductionmentioning

confidence: 99%

Direct Observation and Structural Characterization of the Encounter Complex in Bimolecular Electron Transfers with Photoactivated Acceptors

1997

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The encounter complex between photoexcited quinones Q* and various aromatic donors (ArH) is observed directly by time-resolved ps spectroscopy immediately before it undergoes electron transfer to the ion-radical pair [Q•-, ArH•+]. The encounter complex (EC) is spectrally characterized by distinctive (near IR) absorption bands, and its temporal evolution is established by quantitative kinetics analysis. The structural characterization of the 1:1 encounter complex [Q*, ArH] identifies the cofacial juxtaposition of the donor and acceptor moieties for optimal overlap of their π-orbitals. Further comparisons of the (excited-state) encounter complex with the corresponding (ground-state) EDA complex of aromatic donors and quinones establish its charge-transfer character, which directly relates to electron transfer within the encounter complex. The mechanistic significance of the encounter complex to bimolecular electron transfer is discussed (Scheme ).

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“…[9] With homobenzvalene only products resulting from a rearrangement arise, namely two spirotetrahydrofurans and a spirotetrahydropyran. [9] If the alkene has allylic hydrogen atoms, the radical-ion pair may react to give tetrachlorohydroquinone (TCH) or the respective monocycloalkenyl ether of it, as in the cases of 1,3,5-cycloheptatriene, [10] 1,3-cyclohexadiene, [11] cyclohexene, indene, allyl ethyl ether, [5] 2,3-dihydrofuran, and 3,4-dihydro-2H-pyran. [12] The attack of 3 CA as a diradical at an alkene leads to [2+2] cycloadducts of a dichloroethene moiety of CA, that is, cyclobutanes.…”

Section: Introductionmentioning

confidence: 99%

Photochemical Reactions of Chloranil with Cyclooctene, 1,5‐Cyclooctadiene, and Cyclohexene Revisited

et al. 2010

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Depending on the reaction conditions, excited chloranil ( 3 CA) and cis-cyclooctene (cis-CO) furnished three types of products, which all contain carbocyclic four-membered rings. The illumination of a solution in benzene by light bulbs gave rise to the all-cis 1:1 cycloadduct (11a) in 76 % yield. On its part, this compound reacted with cis-CO under the action of better sources for UV light with the formation of three isomeric 1:2 cycloadducts. Two of them underwent a photochemical dechlorination leading to a cyclobutene derivative. Albeit rather sluggishly, 3 CA and trans-cyclooctene (trans-CO) brought about an unsymmetrical 1:1 and a 1:2 cycloadduct. By contrast, excited 11a reacted smoothly with trans-CO and afforded a 72 % yield of the unsymmetrical 1:2 cy-

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An electron/proton-transfer sequence for quenching chloranil triplets by cyclopolyenes

Cited by 23 publications

References 0 publications

Photo‐cidnp Study of Pyrimidine Dimer Splitting I: Reactions Involving Pyrimidine Radical Cation Intermediates

Photo‐cidnp Study of Pyrimidine Dimer Splitting I: Reactions Involving Pyrimidine Radical Cation Intermediates

Direct Observation and Structural Characterization of the Encounter Complex in Bimolecular Electron Transfers with Photoactivated Acceptors

Photochemical Reactions of Chloranil with Cyclooctene, 1,5‐Cyclooctadiene, and Cyclohexene Revisited

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