Browsing by Author "Ayscough, P. B."

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    Electron Spin Resonance Studies of Elementary Processes in Radiation- and Photo-chemistry: Part 10.—Carboxylic Acid Anhydrides at Cryogenic Temperatures
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Ayscough, P. B.; Oversby, J. P.
    The four carboxylic acid anhydrides, acetic, propionic, n-butyric and iso-butyric, -(-irradiated at 77 K show esr spectra indicating the presence of acyl radicals and radicals formed by loss ol H from the anhydride The latter radicals are derived in part from simple alkyl radical precursors as mav be adduced from experiments on thermal annealing of the irradiated samples. No evidence is found for the presence of trapped radical-anions or cations. Hydrogen atoms react with anhydrides at 77 K to give the same types of radicals that arc formed during y-radtolysis, though in different relative yields.
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    Electron Spin Resonance Studies of Elementary Processes in Radiation- and Photo-chemistry: Part 8.—Thermal and Photochemical Annealing of y-irradiated Glycine
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (6), 1972) Ayscough, P. B.; Mach, K.
    E.s.r. studies of y-irradiatcd single crystals of a-glycinc and glycine-d3 between 77 and 403 K show that the primary radical anions are the only species trapped at 77 K. These arc converted to a mixture of radicals NH3CHCOO' and CH.COOH (or ND^CHCOO" and CH2COOD) below 113 K which change in relative proportions on further annealing. The carboxymethyl radicals disappear only at temperatures approaching 370 K. Differences in the relative stabilities of the two types of radicals in the deuterated and non-dcuterated samples arc observed: these arc thought to have their origin in small differences in crystal parameters. Ultra-violet irradiation of y-irradiated crystals at 77 K produces radicals of structure HNCH2COOH (or DNCH2COOD) apparently by loss of molecular hydrogen.
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    Electron Spin Resonance Studies of Elementary Processes in Radiation- and Photo-chemistry: Part 9.—Carboxylic Esters at Cryogenic Temperatures
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (7), 1972) Ayscough, P. B.; Oversby, J. P.
    Some of the reactions occurring during they-radiolysis of a number of carboxylic esters at cryogenic temperatures have been identified by studying the e.s.r. spectra of trapped intermediate radicals. It appears that the capture of thermal electrons by the ester molecule is followed by dissociation of the radical-anion by one of two possible processes, each leading to the formation of alkyl radicals. Secondary radicals formed by abstraction of hydrogen from the ester appear during thermal annealing. Ultraviolet irradiation of these radicals leads to the regeneration of alkyl radicals. Hydrogen atoms produced by ultra-violet irradiation of mixtures of hydrogen sulphide and carboxylic esters react to give alkyl and acyl radicals, by a mechanism similar to that proposed for carboxylic acids.