Browsing by Author "Ayscough, Peter B."

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    Electron Spin Resonance Studies of Elementary Processes in Radiation- and Photo-chemistry: Part 12.—Fluorinated Carboxylic Acids at Cryogenic Temperatures
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1974, 70 (1-6), 1974) Ayscough, Peter B.; Mach, Karel
    Some information concerning the mechanism of the radiolysis of perfluorinated carboxylic acids is presented from an examination of the e.s.r. spectra of radicals trapped in polycrystallinc samples of the acids between 77 and 300 K. Three types of radicals have been identified iny-irradiatcd samples of RCF2COOH (R = F, CF3, CF3CF2, C6H13, CF2COOH, CF2CF2COOH). These arc (1) parent radical anions RCF2COOH", (2) primary fluoralkyl radicals RCF2, and (3) secondary radicals RCFCOOH. The radical anions lose F~ on thermal annealing to yield additional RdFCOOH radicals, but when samples containing RCF2COOH~ are u.v.-irradiatcd at 77 K these species disappear without the appearance of any identifiable radical product, as do the corresponding species in non fluorinated carboxylic acids. The RCF2 radicals are believed to originate from the cationic species formed in the initial ionization following proton transfer and elimination of CO2.
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    In Situ Radiolysis Electron Spin Resonance Study of the Radical-anions of Substituted Nitroimidazoles and Nitroaromatic Compounds
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (3), 1978) Ayscough, Peter B.; Elliot, A. John; Salmon, G. Arthur
    Reaction of e–aq, (CH3)2ĊOH, (CH3)2CO[graphic omitted] or CO[graphic omitted]2 with a number of substituted nitroimidazoles and nitrobenzenes results in the formation of their radical-anions and in no case were radical-adducts detected. Changes in the e.s.r. spectra of the product species with pH are interpreted in terms of either the protonation of the radical-anion (metronidazole) or the loss of a proton from the radical anion (2-methyl-5-nitroimidazole, 4-nitroimidazole and nitrophenols) and pK values of some of these processes are evaluated. In several cases the dynamics of these acid–base reactions influence the linewidths of the e.s.r. spectra.
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    Kinetic Electron Spin Resonance Spectroscopy Part 61.—Formation and Termination Reactions of Aliphatic Radicals by Reductive Dissociation of Halogeno-compounds
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Ayscough, Peter B.; Lambert, Graham
    The reactions of hydroxy-alkyl radicals with a variety of aliphatic halogeno-compounds RX have been studied. By examining the effects of varying concentrations of RX on the concentration and lifetime of the hydroxy-alkyl radicals it is shown that these are replaced by radicals R· produced by electron transfer to RX and subsequent loss of X–. Peak intensity anomalies are satisfactorily explained in terms of a hyperfine energy induced E–A polarization plus a contribution from an initial (emissive) polarization. Self-termination rate constants for nine aliphatic radicals have been determined. These rate constants are in the range 3 × 108 to 5 × 109 dm3 mol–1 s–1 in propan-2-ol at 300 K and have an inverse correlation with molecular mass. The problems associated with measurements of rate constants for the electron transfer step are discussed. For the reaction of Me2ĊOH with trichloroacetic acid the value (6.1 ± 1.9)× 106 dm3 mol–1 s–1 was obtained in propan-2-ol at 293 K.