- Chemically induced dynamic electron polarization studies on photolysis of hexaphenyldisilane, -digermane and -distannane
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EPR signals of the triphenylsilyl and triphenylgermyl radicals were observed for the first time in fluid solution by direct photolysis of hexaphenyldisilane and hexaphenyldigermane. Observed electron spin polarization was interpreted in terms of a triplet mechanism (TM). Along with the main signal, the 29Si isotope signal was also observed and the polarization was tentatively explained by combination of a TM and a radical pair mechanism. An electron density on the silicon atom of the silyl radical was determined as 0.52 from the isotropic hyperfine coupling constant of 29Si. The triphenylstannyl radical was not observed with the time resolution (ca. 80 ns) of our system.
- Saiful,Ohba,Mochida,Yamauchi
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- The first direct observation of magnetic field effects on the dynamic behavior of radical pairs involving group 14 silicon and germanium centered radicals
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Laser flash photolysis was performed on micellar solutions and oil emulsions of organosilicon and organogermanium compounds ((aryl)nMen-4E: E = Si or Ge) in the absence and presence of magnetic fields at room temperature. The dynamic behavior of the silyl and germyl radicals formed upon decomposition of the triplet states was directly observed. The lifetime of the radical pair of group 14 element centered and aryl radicals and the yields of the escaped silyl and germyl radicals were observed to increase with magnetic field strength increasing from 0 to 1.35 T.
- Wakasa, Masanobu,Sakaguchi, Yoshio,Hayashi, Hisaharu
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- Free radicals from cyclic enones: An electron paramagnetic resonance investigation. Part II.1 Radical additions
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The addition of silyl and germyl radicals to a series of substituted cyclopentenones and cyclohexenones has been investigated using EPR spectroscopy. At low temperatures the 3-position is the preferred site for addition unless it is substituted or sterically hindered in which case addition occurs at the carbonyl oxygen. The latter process is also favoured at higher temperatures but no evidence has been obtained for either addition at the 2-position or for an intramolecular migration following initial attack at the 3- or 2-position.
- Hudson, Andrew,Waterman, Daniel,Della Bona, Maria Antonietta,Alberti, Angelo,Altieri, Andrea,Benaglia, Massimo,Macciantelli, Dante
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p. 2255 - 2260
(2007/10/03)
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- Organosilanes as Radical-based Reducing Agents with Low Hydrogen Donating Abilities
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Me3SiSi(H)Me2, Me3SiSiMe2Si(H)Me2, and (Me3Si)3SiSi(H)Me2 have been used as radical-based reducing agents for a variety of organic substrates.Rate constants for the reaction of primary alkyl radicals with these silanes have been measured over a range of temperature by using the neophyl rearrangement as a radical clock.Some kinetic data have also been obtained for phenyl substituted silanes.The experimental findings are complemented by ab initio MO studies, at different levels of theory, which predict the Si-H bond dissociation energies of PhSiH3, Ph2SiH2, and XSiH2SiH2-H, where X = H, Me and SiH3.The radical trapping abilities of these silanes and other common radical-based reducing agents are compared.
- Ballestri, Marco,Chatgilialoglu, Chryssostomos,Guerra, Maurizio,Guerrini, Andrea,Lucarini, Marco,Seconi, Giancarlo
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p. 421 - 425
(2007/10/02)
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- Fluorescence of Silyl and Germyl Ketones and Their Primary Photochemical Processes
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Dual fluorescence was observed for several mono- and bis-silyl and -germyl ketones in solution at room temperature.From their fluorescence spectra, excitation spectra, quantum yields, and time profiles, the observed fluorescence was assigned to the S2 (the second lowest excited singlet state) --> S0 (the ground state) one and the S1 (the lowest excited singlet state) --> S0 one.For the employed mono-M ketones (PhnMe3-nMCOPh, M=Si or Ge), their S2 lifetimes in cyclohexane were shorter than 160 ps and their S1 ones lay between 0.8 and 2.5 ns.For bis(triphenylsilyl) ketone in cyclohexane, its S2 lifetime was 160 ps and its S1 one as long as 460 ns.Norrish type I cleavage of these ketones in solution was also studied with time-resolved optical absorption and ESR techniques.
- Wakasa, Masanobu,Mochida, Kunio,Sakaguchi, Yoshio,Nakamura, Junko,Hayashi, Hisaharu
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p. 2241 - 2246
(2007/10/02)
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- RADICALS DERIVED FROM MONOTHIOANTHRAQUINONE (TAQ): AN ESR INVESTIGATION
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Reduction of monothioanthraquinone (TAQ) under a variety of conditions leads to the formation of the corresponding radical anion.ESR studies indicate that Group 14 organometallic radicals react with TAQ by selectively adding to the carbon-sulphur double b
- Alberti, Angelo,Benaglia, Massimo,Hudson, Andrew
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p. 537 - 540
(2007/10/02)
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- LASER-PHOTOLYSIS STUDY OF ARYL-SUBSTITUTED SILYL AND STANNYL ANIONS
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Photochemical primary processes of aryl-substituted silyl and stannyl anions were studied at room temperature.The silyl and stannyl radicals generated were observed directly by laser-photolysis.
- Mochida, Kunio,Wakasa, Masanobu,Sakaguchi, Yoshio,Hayashi, Hisaharu
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p. 773 - 776
(2007/10/02)
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