- PHOTODISSOCIATION OF AROMATIC THIOLS AND DISULFIDES
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For the first time, the quantum yields of cleavage of SS and SH bonds in a disulfide and a thiol and also the extinction coefficient of the photoinduced aminophenylthiyl radical were determined, on the basis of which the relation of the photodissociation
- Borisevich, N. A.,Malkin, Ya. N.,Ruziev, Sh.,Mel'nichuk, S. V.,Tikhomirov, S. A.,et al.
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- Magnetic Field Effect on the Photodecomposition of p-Aminophenyl Disulfide in a Micellar Solution
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Upon laser flash photolysis of p-aminophenyl disulfide at room temperature, the radical pair of two p-aminophenylthiyl radicals was found to be generated by direct excitation and triplet sensitization in the magnetic field range 0-1.35 T.Only in the case
- Wakasa, Masanobu,Sakaguchi, Yoshio,Hayashi, Hisaharu
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- Photochemical properties of excited triplet state of 6H-purine-6-thione investigated by laser flash photolysis
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Photochemical reactions of 6H-purine-6-thione (PuT) via the excited triplet state [3(PuT)*] have been studied by means of laser flash photolysis in organic solvents. Transient absorption bands at 475 and 690 nm were assigned to 3(PuT)*. Intersystem quantum yield and the lowest triplet energy of 3(PuT)* were evaluated to be 0.99 and 63 kcal/mol, respectively. The self-quenching rate constant is quite large (2.3×109 M-1 s-1 in THF). In photoinduced electron transfer, 3(PuT)* acts as electron acceptor for tetramethylbenzidine, while 3(PuT)* acts as electron donor for p-dinitrobenzene. Rate constants for H-atom abstraction (khT) of 3(PuT)* from benzenethiols, tocopherol, and 1,4-cyclohexadiene are on the order of 108 M-1 s-1. From the Hammett plots of khT for substituted benzenethiols, a negative ρ value indicates that 3(PuT)* has electrophilic character. In the addition reaction of 3(PuT)* toward various alkenes, the electrophilic character of 3(PuT)* was also confirmed. By steady-light photolysis of PuT, purine was produced via 3(PuT)* after H-atom abstraction. On combination of these results, the character of the lowest 3(PuT)* was presumed.
- Alam,Fujitsuka,Watanabe,Ito
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p. 1338 - 1344
(2007/10/03)
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- Reduction potentials and kinetics of electron transfer reactions of phenylthiyl radicals: Comparisons with phenoxyl radicals
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The reduction potentials relative to the standard hydrogen electrode (SHE) for a number of para-substituted phenylthiyl radicals (Eo(p-XC6H4S./p-XC6H 4S-)) have been derived from pulse radiolytic studies of electron transfer equilibria which compare their values to those of radicals of known reduction potentials. A ladder combining the reduction potentials for both phenylthiyl and phenoxyl radicals has been established. These reduction potentials have been shown to be self-consistent and are intermediate between those of p-benzosemiquinone radical anion at 0.02 V and phenoxyl radical at 0.79 V. The reduction potential decreases as the electron donating power of the para substituent rises. The substituent effect is, however, much weaker for the phenylthiyl radicals than for their oxygen analogs. These observations demonstrate that the electronic interaction between the sulfur atoms and the aromatic ring system is much less than that which occurs with oxygen atoms. Examination of the rates of electron transfer in terms of the Marcus theory indicates that the reorganization energies of both p-XC6H4O. and p-XC6H4S. radicals are similarly affected by H, CH3, and CH3O substitution. However, the reorganization energies increase substantially for H2N and O- para substituents with the effect being much less for the p-XC6H4S. radicals than for the p-XC6H4O. radicals. These observations are in accord with structural information from spectroscopic and theoretical studies of the radicals which show that in the latter system the substituent groups interact strongly with the aromatic π system.
- Armstrong,Sun, Qun,Schuler
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p. 9892 - 9899
(2007/10/03)
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- Kinetic Study for Spin-Trapping Reactions of Thiyl Radicals with Nitroso Compounds
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The rate constants for the reactions of para-substituted benzenethiyl radicals with nitroso compounds have been determined by flash photolysis.For the benzenethiyl radical the rate constants (M-1 s-1) decreased in the order pentameth
- Ito, Osamu,Matsuda, Minoru
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p. 1937 - 1940
(2007/10/02)
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- Solvent Effects on Rates of Free-Radical Reactions. Addition of the p-Aminobenzenethiyl Radical to Styrene
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Absolute rate constants (k1) for addition of the p-aminobenzenethiyl radical (p-NH2C6H4S.) to styrene in 26 kinds of solvents have been determined by the flash photolysis technique.The relative rate constants for the reverse reactions and the relative equ
- Ito, Osamu,Matsuda, Minoru
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p. 568 - 572
(2007/10/02)
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