Browsing by Author "Kemp, T. J."

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    Electron Spin Resonance Studies of Photo-oxidation by Metal Ions in Rigid Media at Low Temperatures: Part 4.—Survey of Photo-oxidation by the Uranyl Ion
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (11), 1972) Greatorex, D.; Hill, R. J.; Kemp, T. J.; Stone, T. J.
    The long-standing problem of the mechanism of photo-oxidation of organic and inorganic molecules by the UO2+2 ion has been explored in some detail by the matrix isolation method, the detection of trapped substrate-derived radicals being effected by electron spin resonance spectroscopy, mostly using organic matrices at 77 K. A variety of mechanisms is apparent even within a given homologous series, but the most common feature is abstraction of a hydrogen atom from a carbon atom adjacent to an activating group such as —CO—, —CN, —CO2H, —CHO, —OH, —CONH2, —CO2R or from a phosphorus atom; carbon-carbon cleavage is found (sometimes exclusively) with secondary and tertiary alcohols, ketones, some carboxylic acids and diethyl ether. These results are discussed in the light of recent steady-state studies involving comparison of quantum yield and fluorescence quenching data.
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    Electron Spin Resonance Studies of Photo-Oxidation by Metal Ions in Rigid Media at Low Temperatures: Part 3.—Ce(lV) Photo-Oxidations of Aldehydes, Ketones, Esters and Amides
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Greatorex, D.; Kemp, T. J.
    A survey is presented of the primary processes in the photo-oxidation by Ce(IV) ions at 77 K of a variety of organic molecules classified by functional group; these processes have been determined by characterization of the resulting organic free radical by electron spin resonance spectroscopy. Aldehydes RCHO and aldehyde hydrates RCH(OH)2 are oxidized to RĊO and RĊC(OH)2 respectively, although C2H5ĊO disappears at 120 K, producing instead CH3ĊHCHO. Ketones produce either the alkyl radical R from RCOR′ or the radical derived by abstraction of a hydrogen atom from the methylene or methine groups adjacent to the carbonyl group; in some cases both types of radical are discernible. Esters also undergo C—H or C—C fission processes depending on the degree of substitution of the R fragment of RCO2R′, whilst formamide yields a spectrum of ·CONH2. Methyl methacrylate yields a vinylic monomer radical at 77 K which induces polymerization at 175 K to give the polymethyl methacrylate radical.