2348-48-3Relevant articles and documents
Mechanism of Formation of o-Methylbenzyl Radical by Photodissociation of o-Xylene in Solution
Fujiwara, Masao,Tanimoto, Yoshifumi
, p. 5695 - 5700 (1994)
Photodissociation of o-xylene in room temperature n-heptane solution has been studied by means of two-pulse laser-induced fluorescence and transient absorption spectroscopy.Excitation of o-xylene at 266 nm into the S1 state causes the molecule to undergo carbon-hydrogen bond homolysis in its methyl group, resulting in formation of the o-methylbenzyl radical.The fluorescence of the o-methylbenzyl radical has been observed around 500 nm with a lifetime of 4.1 +/- 1.0 ns, when it has been excited with a 308-nm pulse after the photolysis pulse.The absorption of the o-methylbenzyl radical has been obtained with maxima at 309 and 320 nm.The formation raet constant of the o-methylbenzyl radical, (3.1 +/- 0.4)E7 s-1, agrees with the decay rate constant of the fluorescence of o-xylene, (2.7 +/- 0.3)E7 s-1.It is concluded that excitation with one photon at 266 nm followed by vibrational relaxation populates the thermal equilibrium.S1 state of o-xylene, from which predissociation occurs.
Kinetics of the reaction of the TEMPO radical with alkylarenes
Opeida,Matvienko,Bakurova,Voloshkin
, p. 900 - 904 (2007/10/03)
The kinetics of the reaction of the stable radical 2,2,6,6- tetramethylpiperidine-N-oxyl (TEMPO) with a series of alkylarenes containing primary and secondary benzyl C-H bonds was studied by ESR, and the reaction rate constants were determined. The scheme
Reaction pathways involved in the quenching of the photoactivated aromatic ketones xanthone and 1-azaxanthone by polyalkylbenzenes
Coenjarts,Scaiano
, p. 3635 - 3641 (2007/10/03)
The reactions of the photoexcited aromatic ketones, xanthone and 1-azaxanthone, with polyalkylbenzene donors yields the corresponding ketyl radicals as detected by nanosecond laser flash photolysis. On the basis of formation of these photoreduced products, the quenching of the photoexcited species is expected to occur either by a one-step hydrogen abstraction from the donor, electron transfer followed by proton transfer from the donor, or by formation of a charge-transfer type encounter complex prior to hydrogen atom transfer. The reactions of triplet xanthone and triplet 1-azaxanthone with polyalkylbenzene donors in acetonitrile were investigated to probe the effect of the nature of the triplet state and the redox properties on the relative importance of each quenching pathway. Determination of bimolecular rate constants, as well as analysis of kinetic isotope effects and ketyl radical yields, suggests that for both xanthone and 1-azaxanthone the quenching process is dominated by formation of charge-transfer encounter complexes between excited-state aromatic ketone acceptor and ground-state polyalkylbenzene donor. The reactivites of the xanthone π,π* triplet and 1-azaxanthone n,π* triplet toward these donors is shown to be governed by their reduction potentials, with their electronic configuration being unimportant to the kinetics of encounter complex formation. The only exception to this is found when sterically encumbered polyalkylbenzene donors are employed. Results with these compounds suggest that π,π* and n,π* states form encounter complexes of different structure which affects their ability to react with hindered donors. Additionally, product yields with all of the donors are controlled by both the extent of charge transfer within encounter complexes and the encounter complex structure.
