Coexistence of Hydrogen Atom Transfer Reactions through and not through Triplet Ion Pair between <i>p</i>-Chloranil and Durene

Photoinduced coupling of an acetylene with a quinone in two wavelength regions (λDB and λCT) can be regioselective to yield a single quinone methide adduct when various diarylacetylenes (DA) and 2,6-dichlorobenzoquinone (DB) are used. Thus, the direct photoexcitation of DB at λDB = 355 nm or the specific activation of the 1:1 electron donor−acceptor complex [DA,DB] at λCT = 532 nm both lead to the transient ion-radical pair [DA •+,DB •-], which is established by time-resolved (ps,ns) spectroscopy. Competition between back electron transfer (k BET) and ion-radical pair collapse (k C) to the distonic adduct DA-DB, as described in Schemes and , limits the quantum yields for both photochemical processes in Table . The biradical nature of the distonic adduct in Scheme accommodates the various facets of acetylene reactivity and unique regioselectivity to yield the same quinone methide by both actinic processes. In a more general context, the electron-transfer mechanism established by the charge-transfer excitation of [DA,DB] provides compelling evidence that the Paterno−Büchi coupling (by direct excitation of DB) can proceed via the same sequence of reactive intermediates.

show abstract

“…Diffusional quenching of the excited quinone DB * results in the formation of the triplet ion pair in eq 11 …”

Section: Referencesmentioning

confidence: 99%

Paterno−Büchi Coupling of (Diaryl)acetylenes and Quinone via Photoinduced Electron Transfer

1998

View full text Add to dashboard Cite

show abstract

“…56 In particular, an inert salt (M+ X-) undergoes rapid exchanges with the contact ion pair [eqn. (8)], as well as with the solvent-separated ion ESE", CA'-+ M + , X-c M + , CA'-+ ESE", X-(8) pair. Since the individual ions ESE*+ and CA'-become separated in eqn.…”

Section: Microdynamics Of Contact Ion Pairs: Internal Return Versus S...mentioning

confidence: 99%

Photoinduced electron transfer from enol silyl ethers to quinone. Part 2. Direct observation of ion-pair dynamics by time-resolved spectroscopy

Bockman¹,

Kochi²

1996

J. Chem. Soc., Perkin Trans. 2

View full text Add to dashboard Cite

“…9 Chloranil durene system in 1,2-dichloromethane revealed the presence of both CIP and SSIP in equilibrium. 10 But in such studies reported thus far, there is no structural evidence to differentiate the nature of ion pair formed in different solvent polarity.…”

Section: Introductionmentioning

confidence: 99%

Influence of Solvent on Photoinduced Electron-Transfer Reaction: Time-Resolved Resonance Raman Study

Mohapatra

Umapathy

2009

J. Phys. Chem. A

View full text Add to dashboard Cite

Time-resolved resonance Raman spectroscopy (TR3) has been used to study the effect of solvent polarity on the mechanism and nature of intermediates formed in photoinduced electron-transfer reaction between triplet flouranil ((3)FL) and tetramethylbenzene (TMB). Comparison of the TR3 spectra in polar, nonpolar, and medium polar media suggests that formation of radical anion due to electron-transfer reaction between (3)FL and TMB is favored in more polar solvents, whereas ketyl radical formation is more favored in less polar media. Compared to ketyl radical, the extent of radical anion formation is negligible in nonpolar solvents. Therefore, it is inferred that in nonpolar media ketyl radical is mainly generated by hydrogen-transfer reaction in the encounter complex between (3)FL and TMB. In solvents of medium polarity, the ion-pair decay leads to the formation of both ketyl radical and ketyl radical formed from the encounter between triplet state and the donor. Thus, competition between the formation of ketyl radical and ion pair is influenced by the solvent polarity. The nature of the ion pair in different solvent polarity has been investigated from the changes observed in the vibrational frequency of (fluoranil) FL part of the complex.

show abstract

Coexistence of Hydrogen Atom Transfer Reactions through and not through Triplet Ion Pair between p-Chloranil and Durene

Cited by 54 publications

References 31 publications

Paterno−Büchi Coupling of (Diaryl)acetylenes and Quinone via Photoinduced Electron Transfer

Paterno−Büchi Coupling of (Diaryl)acetylenes and Quinone via Photoinduced Electron Transfer

Photoinduced electron transfer from enol silyl ethers to quinone. Part 2. Direct observation of ion-pair dynamics by time-resolved spectroscopy

Influence of Solvent on Photoinduced Electron-Transfer Reaction: Time-Resolved Resonance Raman Study

Contact Info

Product

Resources

About