Browsing by Author "Maccoll, Allan"

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    Chlorine Kinetic Isotope Effects Thermal Decomposition of 1-Chlorocthane and Evaluation of Possible Models of Activated Complex
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Maccoll, Allan; Mruzek, Margaret N.
    Chlorine kinetic isotope effects have been investigated for the pyrolysis of 1-chloroethane in a static system in the temperature range 395–482°C. The temperature dependence of the kinetic isotope effects has been determined. The mass spectrometric isotope ratio analysis was made on the hydrogen chloride produced. A model for the chlorine involvement in the four-centre activated complex is advanced and various alternative geometries are evaluated in terms of heavy-atom approximation and first-order high temperature kinetic isotope effects. Best agreement with the experimentally determined values of k35/k37 is given by a model of the activated complex which involves chlorine participation in the reaction coordinate with three degrees of freedom. The effect of the individual geometric parameters that includes the C—Cl stretching, the C—C—Cl bending and the C—CH3 stretching and their combination, is evaluated.
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    Heavy Atom Kinetic Isotope Effects: Part 1.—Liquid Phase Decarboxylation of Malonic Acid
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (5), 1973) Loudon, Alexander G.; Maccoll, Allan; Smith, David
    The 13C/12C isotope effects in the decomposition of all the mono-13C malonic acid species have been determined. Three rate constant ratios have been determined, and two of these are in good agreement with the values recorded in the literature. The third has not previously been reported. The present results are consistent with a six-centred transition state for this reaction.
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    Heavy Atom Kinetic Isotope Effects: Part 2.—Nitrogen Isotope Effects in the Decomposition of Aqueous Aromatic Diazonium Salts
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (5), 1973) Loudon, Alexander G.; Maccoll, Allan; Smith, David
    The rate constant ratio l4k/l5k was determined for the decomposition of some diazonium fluoro- borates in aqueous solution in both the presence and absence of added salts. The implications of the results for the mechanism of these reactions are discussed.
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    Homogeneous Gas Phase Pyrolysis of 7V-t-Butylacetamide
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1973, 69 (6), 1973) Maccoll, Allan; Nagra, Surgit S.
    The kinetics of the gas phase pyrolysis of N-t-butylacetamide have been studied in a static system over the temperature range 385–465°C. The decomposition occurs by two simultaneous, homogeneous and unimolecular processes. The major process (1) is the elimination of isobutene and the formation of acetamide; the minor process (2) is the elimination of t-butylamine and the formation of ketene. CH3CONHC(CH3)3[graphic omitted](CH3)2C[double bond, length as m-dash]CH2C + CH3CONH2(1), CH3CONHC(CH3)3[graphic omitted](CH3)3CNH2+ CH2[double bond, length as m-dash]C[double bond, length as m-dash]O. (2) The rate constant for reaction (1) in the Arrhenius form is k1= 1012.42 exp (– 51 540/RT) s–1(R in cal mol–1 K–1). The acetic acid formed by subsequent decomposition of the acetamide catalyses the formation of t-butylamine and the rate constant for this bimolecular process between 400–452°C is given by k3= 1013.56 exp (– 34 950/RT) cm3 mol–1 s–1. The transition state for reaction (1) is believed to be six-centred.