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  • 1990-1994  (227)
  • 1985-1989
  • 1910-1914
  • 1992  (227)
  • Physical Chemistry  (227)
  • 101
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The kinetics of the hydrolysis of benzohydroxamic acid have been investigated in hydrochloric, sulphuric and perchloric acids in 10% (v/v) dimethyl sulphoxide - water at 55 °C. Activation parameters were also determined. Rate correlation by the Cox - Yates excess acidity method shows an A-2 mechanism involving rapid pre-equilibrium protonation of the substrate followed by rate-limiting attack of water at the carbonyl carbon atom to form a tetrahedral intermediate which collapses, in a fast step, to the products.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 102
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 44-54 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The molecular recognition properties of 18 acyclic imides were studied to evaluate the relative contributions of conformational, hydrogen bonding and crystal packing forces to the stabilization of specific aggregate patterns in the solid state. The crystal structure of diisobutyramide and the aggregate patterns of the 18 imides are presented. The stabilization by hydrogen bonding was found to override the conformational preferences of imides, while packing forces often precluded the formation of the most stable hydrogen bonded aggregate. The aggregate patterns of imides were also found to be a function of the type of substituents present as R groups. Imides with R groups of similar shape and size prefer to pack as bifurcated hydrogen bonded chains, whereas dimers or singly hydrogen-bonded chains form when the R groups have significantly different spatial requirements. Analysis of imide aggregate patterns revealed the similar spatial requirements of isopropyl and phenyl groups. The molecular recognition properties of acyclic imides are summarized as a set of hydrogen bond rules, which can be used to design new imide aggregates.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 103
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 55-61 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Long-lived trapped radicals produced during the photopolymerization of butane-1, 4-diol diacrylate (BDDA) were studied by EPR and ENDOR spectroscopy and their thermal decay was followed by EPR measurements at different temperatures (40-120 °C) for kinetic study. The EPR signal showed the superimposition of two different patterns, a three-line and a single-line spectrum. Both EPR patterns decayed following first-order kinetics in the investigated temperature range. Activation parameters of the decay were obtained. The EPR patterns were attributed to the same radical species situated in fluid and in cross-linked regions of the photopolymerized BDDA. Radicals of the latter kind undergo electron spin exchange strong enough to wash out the hyperfine splitting. The single-line width is mainly determined by electron spin dipole-dipole interactions. The ENDOR response is only of the matrix kind, typical of radicals in a solid phase. The present model was also compared with recent literature reports.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 104
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992) 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Materialart: Digitale Medien
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  • 105
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 600-608 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Rates of degradation of the triazine herbicide atrazine are reported, together with an analysis of the sequence of stages involved, using hydroxyl radicals generated by hydrogen peroxide in the presence of UV light and by the pure photochemical reaction. These conditions bring about the displacement of chlorine by hydroxyl, dealkylation of the alkylamino groups and finally deamination of the triazine ring. The significance of these results to water purification is discussed.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 106
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 683-688 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The recent attempts to evaluate the stereoelectronic effects at carboxyl oxygen using Kemp's triacid derivatives are reviewed. Contexts include metal-ion chelation, acidity measurements, intramolecular general base catalysis and nucleophilic substitution. These give a range of 0-8 kcal/mol for the effects, and leave the issue open for more incisive experiments.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 107
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Photochromic molecules such as dihydroindolizines (DHI) containing crown ether units can be ‘tuned’, as far as their properties are concerned, by supramolecular ion binding. Inclusion of the ion in the crown ether cavity yields a new supramolecular species. This species shows special properties of the excited state after guest addition: (a) bathochromic shifts of the photochromic crown ethers and also hyperchromic effects in the UV spectra; (b) fluorescence intensity of one of the photochromic crown ethers is either increased (crown excitation) or decreased (DHI excitation) after addition of alkali metal ions; and (c) in the ground state a large change in reaction rate for the reaction 1,5-electrocyclization betaine (coloured form) to dihydroindolizine is observed in the supramolecular complexes.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 108
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 699-710 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Calix [n] arenes (n= 4 and 6) bearing chiral substituents (R*) on the lower rim (1n) or on the upper rim (4n) were synthesized. The isomers derived from 14 were conformationally immobile and showed different circular dichroism (CD) spectra. In the 1H NMR spectra the proton signals in R* shifted to higher magnetic field when the lower rim is sterically crowded and in the CD spectra a strong CD band appeared. Therefore, the change in the CD spectra is rationalized in terms of R*…π interactions. In contrast, compound 44 was not conformationally immobilized and the CD spectra changed in response to the metal binding to the methoxy oxygens arranged on the lower rim. The specific metal interaction enabled the metal binding event to be detected by the CD technique.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 109
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 715-720 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Fluorocarbon amphiphiles with a 1,3-disubstituted thioglycerol structure form stable unilamellar vesicles. The fluorocarbon bilayer of an amphiphile which has an ammonium salt as head group is an ‘insulator’ for the permeation of hydroxide anions. In the presence or absence of a fluorocarbon nucleophile, hydrolysis of a probe amphiphile carrying a cleavable p-nitrophenyl ester group in the vesicle under alkaline conditions shows a pattern of biphasic kinetics, in which the fast and slow reaction can be attributed to the hydrolysis of probe molecules at outer and inner surfaces of vesicles, respectively. The fact that the slow rate constant always remains constant at 0.25 min-1 at 25°C, independent of the pH of the system and of concentration of the nucleophile, indicates that the slow process is an outward flip-flop process of probe molecules within the fluorocarbon domain.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 110
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The gas-phase unimolecular elimination of the methanesulphonates in the temperature range 289.0-331.4°C and pressure range 18-152.5 Torr follows a first-order rate law. The rate coefficients for the homogeneous reactions are expressed by the following equations: for 3-(o-methoxyphenyl)propyl-1-methanesulphonate log[k1(s-1)] = (12.04 ± 0.32) - [(167.8 ± 3.6) kJ mol-1] (2.303RT)-1 and for 4-(p-methoxyphenyl)butyl-1-methanesulphonate log [k1(s-1)] = (12.82 ± 0.30) - [(175.1 ± 3.4) kJ mol-1] (2.303RT)-1. The oxygen atom of the CH3O substituent in 3-(o-methoxyphenyl)propyl-1-methanesulphonate appears to participate directly in the C-O bond polarization in order to produce some of the cyclic product dihydrobenzopyran. A parallel reaction occurs with 4-(p-methoxyphenyl)butyl-1-methanesulphonate where the p-anisyl substituent participates in the elimination process through a five-membered spiro intermediate for the formation of the cyclic product 6-methoxy-1,2,3,4-tetrahydronaphthalene. The second pathway of this elimination takes place via normal formation of the corresponding unsaturated aromatic hydrocarbons. These reactions are interpreted in terms of an intimate ion-pair type of mechanism.
    Zusätzliches Material: 10 Tab.
    Materialart: Digitale Medien
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  • 111
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 764-768 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The recently proposed similarity approach to the Evans/Dewar concept of aromaticity of transition states was generalized by introducing the second-order similarity index. This generalization is especially convenient for the characterization of antiaromatic transition states in forbidden reactions since, owing to the partial incusion of electron correlation in the second-order index, the detailed specification of their structure in terms of the electron states of these biradicaloid species becomes possible. The results obtained are in complete agreement with the conclusions of independent quantum chemical analyses.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
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  • 112
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 467-470 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Pseudoglyceryl ammonium ion coliposomes constructed from an arachidoyl probe lipid and either stearoyl or palmitoyl host lipids display unusually slow transverse bilayer migration (‘flip-flop’) of the arachidoyl probe molecule compared with the behavior of shorter probe lipids in similar colipsomes. This phenomenon is probably associated with interdigitation of the arachidoyl lipid across the bilayer's midplane.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 113
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A series of bridged calix [4] arenes (5-10 methylene groups in the bridge) were synthesized and transformed into their tetraester derivatives by reaction with ethyl bromoacetate. The stability constants for complexes of the tetraester derivatives with sodium, potassium and silver cations, determined in methanol by spectroscopic or potentiometric techniques, show a drastic decrease (more than 105 for Na +) for the shorter methylene chains. 1H NMR studies demonstrate a conformational rearrangement of the calixarene part to fourfold symmetry to be necessary for the complexation of a cation, which is prevented by the shorter chains. This is further confirmed by the X-ray structure of a tetraester derivative with a CH2CH2COCH2CH2 bridge; crystals were monoclinic, space group P21/c,a = 11.847(2), b = 39.773(5), c = 12 · 127(2) Å, β = 109.24(1), V = 5395.1 Å3, Z = 4, Dx = 1.186 Mg m-3.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 114
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 502-506 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Both the regioselectivity and the reaction rate for the β-cyclodextrin (β-CyD)-induced P-O(3′) cleavage of adenosine 2′, 3′-cyclic phosphate (A 〉 p) to adenosine 2′-phosphate are greatly promoted by KF. The promoting activity of KF is much larger than that of KCl. KF amplifies the difference in the chemical circumstance between the P-O(2′) and the P-O(3′) bonds of A 〉 p, induced by β-CyD on complex formation with A 〉 p. The higher activity of KF is ascribed to absence of complex formation of F- ion with β-CyD, which results in deeper penetration of A 〉 p into the cavity of β-CyD.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 115
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 518-528 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The formation of micelles, vesicles and monomolecular layers by amphiphilic cyclodextrins possessing hydrophobic ester groups on the secondary hydroxyl face is described. The physico-chemical properties of these self-organizing systems were studied by dynamic light scattering, variable-temperature 1H NMR, the use of lanthanide shift reagents, deposition of Langmuir layers, variable-temperature solubility measurements and aqueous and non-aqueous surface tension activity measurements. The results are interpreted in terms of the cylindrical geometry of the compounds which, coupled with the presence of a large planar polar head group, lead to the formation of self-organized systems both in polar organic solvents and also at the air-water interface.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 116
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 540-548 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Although the cyclen - Co(III) complex has exhibited amongst the greatest rate accelerations in acyl and phosphoryl transfer reactions, this catalytic unit has not been used previously in the design of an artificial metalloenzyme. For this study, β-cyclodextrin derivatives of cyclen - Co(III) with attachments to the primary and secondary sides of the cyclodextrin torus were synthesized. The primary-side cyclodextrin-cyclen-Co(III) conjugate accelerates the hydrolysis of p-nitrophenylacetate by a factor of 1000 (pH 7.0, 25°C) in comparison with the water-catalyzed reaction. Maximum reactivity occurs at pH 7, consistent with the known pKa values and hypothesised mechanism of action of Co(III) complexes. The secondary-side cyclodextrin-cyclen-Co(III) conjugate is less reactive towards p-nitrophenylacetate hydrolysis under saturating conditions. Reactivities towards an azide, a phosphonate and a phosphate triester were in each case less than five times greater than the buffer-catalyzed rate.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 117
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 567-574 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Analysis of the sum of two-centre terms obtained from semi-empirical molecular orbital calculations into atom-pair interactions revealed a unique behaviour of 1,4-non-bonded atom-pair interactions compared with 1,5- and longer range interactions. Explicit inclusion of a special 1,4-non-bonded interaction term in an MM2-like molecular mechanics scheme gave a test force field with good performance.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 118
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 590-594 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Solvent effects on the Hammett ρ value for the cathodic reduction of substituted benzophenones were determined. The electrochemistry of a series of 11 compounds was studied in acetonitrile, acetone, dimethyl sulphoxide, propylene carbonate, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide and hexamethylphosphoric triamide. The ρ values for the reversible one-electron transfer are described by the Lewis acid-base model ρ = - 0.006AN + 0.003DN + 0.391, where AN = solvent acceptor number and DN = solvent donor number.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 119
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The reactions of n-butylamine and piperidine with 1-chloro-2, 4-dinitrobenzene and 4-chloro-3-nitrotrifluoromethylbenzene were studied in n-hexane, benzene and mesitylene. The reactions seem to follow a bimolecular SNAr mechanism for both substrates and amines. However, whereas in n-hexane they are base catalysed, in the aromatic solvents only mild acceleration is observed. The different behaviour of these reactions in the aromatic solvents in comparison with hexane is explained by the specific solvent effect exerted by the aromatic compounds, which solvates the aromatic reactant preferentially in view of its electron-donor properties. These conclusions were confirmed by kinetic studies in hexane-aromatic solvent binary mixtures. It can be concluded that the presence of electron-donor solvents may inhibit SNAr reactions when association constant of the solvent with the substrate is greater than the EDA constants between the reactants. These specific solvent effects could also explain why only mild acceleration is observed in aromatic solvents.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 120
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 614-616 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The MNDO, AM1 and PM3 semi-empirical methods were used to calculate the equilibrium points and transition-state structures of the rotational barriers of ethane and all methyl-substituted propanes and butanes. Force constant methods were used to ensure proper geometries. In general, AM1 barriers tend tobe lower than MNDO calculated ones, which are themselves generally lower than experiment. The PM3 values are closest to experiment, ranging from slightly above to slightly below the experimental values. The complexity of various possible rotational minima makes the development of empirical rules to predict barrier heights difficult.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 121
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Structures in CD3OD—CDCl3 mixtures of pyridino-18-crown-6 and diesterpyridino-18-crown-6 complexes with primary ammonium cations containing an α-phenyl group were found to be significantly different. The π-π overlap between the α-phenyl group of the ammonium cation and the pyridine ring of the ligand occurs in the pyridino-18-crown-6 complexes but not in the diesterpyridino-18-crown-6 complexes. The solution structure of a diesterpyridino-18-crown-6 complex with an α-phenyl-containing primary ammonium cation was also found to differ markedly from the corresponding crystal structure in that π-π overlap occurs in the crystal structure, but not in the solution structure.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 122
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The structure of the acetone complex of tri-o-thymotide was solved by single-crystal x-ray diffraction. The acetone molecule is situated on the twofold axis of the cage and shows no sign of unusual disorder. Solid-state 2H and 13C NMR were used to show that, in addition to fast methyl group rotation, there is a rotation of the acetone molecule about the carbonyl bond. The motion is best described as a twofold flip plus the temperature-dependent population of a secondary site 63 ± 10° away from the minimum energy position. Molecular modelling calculations were used to confirm the potential shape, which was remarkably sensitive to methyl group orientation. 2H spin-lattice relaxation was used to derive an activation energy of 13 ± 6 ± 0 ± 8 kJ mol-1 for the twofold flips, and the secondary site was shown to be energetically less favourable by 4.4 ± 0.5 kJ mol-1 from the temperature dependence of the line shape. Neither motion is seen in the diffraction experiment.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 123
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 5 (1992), S. 803-811 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The effect of a wide variety of metal ious and metal ion complexes on the hydrolysis of uridine 2′,3′-cyclic monophosphate was studied over the pH range 4.5-8.0. The greatest rate accelerations observed were 107-108-fold. The kinetic data obtained are interpreted in terms of a mechanism involving arapid monodentate binding of the metal ion to the monoanionic phosphodiester and a subsequent intracomplex participation of the metal-bound hydroxo ligand, either as a nucleophile attacking the tetracoordinated phosphorus or as a base facilitating an intermolecular attack of a water molecule. No effect on the product distribution between uridine 2′- and 3′-monophosphates was observed.
    Zusätzliches Material: 7 Ill.
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  • 124
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 127-143 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reactions of dimethylsilylene, SiMe2, generated by laser flash photolysis from pentamethyldisilane and octamethyltrisilane, and detected via its 457.9 nm absorption, have been investigated with a number of oxygen containing molecules, including oxygen itself, carbon monoxide, water, alcohols, and ethers at 295 K. Some substrate molecules were deuterated. Apart from CO, all molecules reacted with SiMe2 with second order rate constants (in cm3 molecule-1 s-1) in the range 7.7 ± 10-14 to 4.7 ± 10-11.While most of the reactions of SiMe2 studied went to completion those with dimethylether and tetrahydrofuran were partially reversible. The reaction of SiMe2 with oxirane was pressure dependent.The data are generally consistent with a mechanism involving initial formation of a donoracceptor, zwitterionic complex. In the case of reaction with alcohols, there is a small overall isotope effect, suggesting formation of a complex followed by rapid H-transfer, which only marginally affects the rate. In the case of ethers, complexes are formed which (i) may react further (Me2Si…oxetane), (ii) may react further but also reversibly decompose (Me2Si…oxirane), or (iii) do not seem to react further (Me2Si…OMe2, Me2Si…THF) but partially redissociate. The donor-acceptor bond strength has been estimated in these last cases to be ca. 40 kJ mol-1. Supporting arguments and mechanistic details of all reactions investigated are presented.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 125
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 145-154 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A study was made on the kinetics and mechanism of the reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ 2{\rm MnO}_4 ^- + {\rm S} \longrightarrow 2{\rm MnO}_4 ^{2-} + {\rm Product} $$\end{document} in aqueous solutions of 0.10 to 2.0 mol dm-3 alkaline concentrations. The substrates (S) applied were ethane-1,2-diol (ethylene glycol), glycol aldehyde, glycollic acid, and glyoxylic acid. Glycol aldehyde and glyoxylic acid were present in the form of dihydrate. In each case alkoxy anion is the reactive form and the KB constant of deprotonation can be calculated from the kinetic data. A mechanism based on electron abstraction is suggested. Manganate reacts with these substrates much slower than permanganate.
    Zusätzliches Material: 5 Tab.
    Materialart: Digitale Medien
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  • 126
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 155-164 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of reversible complexation of oxalatopentaammine cobalt(III) with Ni2+ has been investigated in MeOH + water media (0-50 (v/v) % MeOH) at 15.0-35.0°C and I = 0.10 mol dm-3. Analysis of rate data indicates that the monobonded complex [(NH3)5 · CoOCOCO2Ni]3+ in which Ni2+ is bound to the end carboxylate group is the possible reaction intermediate. The formation and dissociation rates of such a species are rate limiting for the overall formation and dissociation of the binuclear species, in which Ni2+ is chelated by the oxalate moiety. The rate and activation parameters for formation and dissociation of the binuclear species are moderately solvent sensitive and solvent structural effects are discernible in the nonlinear variations of ΔH≠ and ΔS≠ with solvent composition. The log kr vs. Grunwald Winstein parameter (YButCl) plot for the dissociation of the binuclear species is markedly nonlinear.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 127
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 309-317 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Investigation of the photochromic system TPID/CHCl3 (TPID = triphenylimidazolyl dimer) in a CSTR provided the first example of isothermal photochemical bistability. The reaction mechanism was established and the relevant kinetic and spectroscopic parameters were estimated experimentally. In order to predict the quantitative dynamic behavior of the TPID/CHCl3 system these parameters were refined numerically using batch reactor data.The adjusted model simulates very accurately bistability either as a function of residence time τ, or as a function of incident photon flux I0.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 128
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 319-344 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Experimental profiles of stable species concentrations and temperature are reported for the flow reactor oxidation of ethanol at atmospheric pressure, initial temperatures near 1100 K and equivalence ratios of 0.61-1.24. Acetaldehyde, ethene, and methane appear in roughly equal concentrations as major intermediate species under these conditions. A detailed chemical mechanism is validated by comparison with the experimental species profiles. The importance of including all three isomeric forms of the C2H5O radical in such a mechanism is demonstrated. The primary source of ethene in ethanol oxidation is verified to be the decomposition of the C2H4OH radical. The agreement between the model and experiment at 1100 K is optimized when the branching ratio of the reactions of C2H5OH with OH and H is defined by (30% C2H4OH + 50% CH3CHOH + 20% CH3CH2O) + XH. As in methanol oxidation, HO2 chemistry is very important, while the H + O2 chain branching reaction plays only a minor role until late in fuel decay, even at temperatures above 1100 K.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 129
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 345-358 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the gas-phase reactions of 1,4-benzodioxan, 2,3-dihydrobenzofuran, and 2,3-benzofuran with OH radicals and O3 have been studied at 298 ± 2 K and atmospheric pressure of air and the products have also been investigated. 1,4-Benzodioxan and 2,3-dihydrobenzofuran were chosen as volatile model compounds for dibenzo-p-dioxin and dibenzofuran, respectively. The rate constants, or upper limits thereof, for the O3 reactions were (in cm3 molecule-1 s-1 units): 1,4-benzodioxan, 〈1.2 × 10-20; 2,3-dihydrobenzofuran, 〈1 × 10-19; and 2,3-benzofuran, (1.83 ± 0.21) × 10-18. Using a relative rate method, the rate constants for the OH radical reactions (in cm3 molecule-1 s-1 units) were: 1,4-dibenzodioxan, (2.52 ± 0.38) × 10-11; 2,3-dihydrobenzofuran, (3.66 ± 0.56) × 10-11; and 2,3-benzofuran, (3.73 ± 0.74) × 10-11. Salicylaldehyde was observed as a product of the OH radical-initiated and O3 reactions of 2,3-benzofuran, with measured formation yields of 0.26 ± 0.05 and 0.13 ± 0.07, respectively.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 130
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 359-368 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics and mechanism of the reaction of Ni(II) with heptane-,5-dione (Hhptd) have been investigated in concentrated sodium perchlorate aqueous solutions at 298 K. The kinetic data in the different media are consistent with a mechanism in which Ni(II) reacts with the enol form of the ligand. The observed positive salt effect on the rate of the reaction of formation of the complex Nihptd+ is rationalized taking into account the increase of the rate of water exchange from the first solvation sphere of the metal ion to the bulk solvent when increasing salt concentration.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 131
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 369-383 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction mechanism of the halogen (Cl and Br)-atom initiated oxidation of C2H4 was studied using the long path FTIR spectroscopic method in 700 torr of air at 296 ± 2 K. Among the major halogen-containing products were X—CH2CHO, X—CH2CH2OH, and X—CH2CH2OOH (X = Cl or Br) which were shown to be formed via the self-reaction of the X—CH2CH2OO radicals, i.e., 2X—CH2CH2OO → 2X—CH2CH2O + O2; (a) 2X—CH2CH2OO → X—CH2CHO + X—CH2CH2OH + O2 and (b) followed by X—CH2CH2O + O2 → X—CH2CHO + HO2 and X—CH2CH2OO + HO2 → X—CH2CH2OOH + O2. From the observed yields of X—CH2CHO and X—CH2CH2OH the branching ratios for reactions (a) and (b) were determined to be ka/kb = 1.35 ± 0.07(2σ) for both X = Cl and Br. In addition, the O2-dependence of the rate constant for the Br + C2H4 reaction was determined by the relative rate technique as a function of O2 partial pressure from 140 to 700 torr at 700 torr total pressure of N2/O2 diluent. Rate constants for the reactions of Cl-atoms with Cl-CH2CHO and Br-atoms with Br-CH2CHO were also determined to be [4.3 ± 0.2(2sigma;)] × 10-11 and less than or equal to [1.83 ± 0.11(2σ)] × 10-13 cm3 molecule-1 s-1, respectively.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 132
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 133
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 385-410 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The oxidation of n-heptane has been studied in a jet-stirred flow reactor in the temperature range 950-1200 K at atmospheric pressure for a wide range of fuel-oxygen equivalence ratios (0.2 to 2.0). A chemical kinetic reaction mechanism developed from previous studies on smaller hydrocarbons and extended to C6 and C7 species was used to reproduce the experimental data. Good agreement between computed and measured concentrations of major chemical species was obtained for the entire range of experimental conditions. Sensitivity analyses were carried out to identify the reactions having the greatest influence on the modeling results. The major reaction paths for n-heptane consumption and for the formation of the main products have been identified.In addition n-heptane ignition delays behind a reflected shock wave measured by other investigators were used to validate the present reaction mechanism at higher temperature and pressure.
    Zusätzliches Material: 12 Ill.
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  • 134
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 411-419 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Permanganate ion oxidizes glycine in phosphate buffered solutions, and the product obtained was identified as a soluble form of colloidal manganese dioxide. The influence of glycine on the colloidal product shows glycine concentration changes extinction coefficients of the colloidal product, and only when the influence of glycine has been eliminated, the theoretical and experimental reaction rates coincide. The dependence of the rate of flocculation on several experimental variables was also considered.
    Zusätzliches Material: 3 Ill.
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  • 135
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 421-432 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using BAC-MP4 potential-surface parameters, supplemented by an MP2 normal-mode analysis at one transition state, and statistical theoretical methods, we have computed thermal rate coefficients for the reactions, and Over the entire temperature range considered, 300 K 〈 T 〈 3300 K, reaction (2) is the dominant product channel. The theoretical predictions are in excellent agreement with the experimental results available for k2 and k-1, the rate coefficient for the reverse of reaction (1). Modified Arrhenius expressions are given for k1, k-1, and k2. In addition, we identify and discuss a weakness in utilizing a Hartree-Fock normal-mode analysis in the prediction of k2. The present result for k2 is much smaller than that used in the initial modeling of the RAPRENOx process. The implications of this are discussed.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 136
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 433-445 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this study a ring dye laser spectrometer was employed for in-situ measurements of CH concentrations in the reaction zone behind shock waves. The time dependent absorption in the Q-branch of the A2Δ  -  X2Π band of CH at 431.1311 nm caused by the formation and consumption of CH radicals during the shock induced pyrolysis of a few ppm methane in argon was recorded. The CH concentration could directly be calculated from the measured absorption by applying the Lambert-Beer law. By adding a few percent CO to the initial mixtures, the CH concentration profiles were significantly perturbed. Both the perturbed and unperturbed CH concentration profiles have been compared with those calculated from reaction kinetic simulations. A reaction mechanism describing the CH concentration history in the CH4/Ar and CH4/CO/Ar systems between 2900 K and 3500 K was developed. By a fitting procedure, a value of k1 = 1.85 × 1011 cm3 mol-1 s-1 was obtained for the most important perturbation reaction CH + CO → C2O + H.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 137
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 447-454 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of solvolysis of the title compound (QAc) in undried DMSO-d6 to give 4-(1-ethoxycarbonyl-1-cyano)methylquinoline (QH) and HOAc at ambient temperature were investigated by 1H nmr spectrometry. With a limited excess of water the solvolysis follows a three-step process of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm QAc} + {\rm H}_2 {\rm O}\mathop \to \limits^{k_1} {\rm QH} + {\rm HOAc}, $\end{document} , and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Ac}_{\rm 2} {\rm O} + {\rm H}_2 {\rm O}\mathop \to \limits^{k_3} {\rm 2\,HOAc}, $\end{document} where k2 〉 k1 and k3 〈 k1. Addition of pyridine-d5 to the reaction mixture markedly catalyzes the overall solvolysis, while addition of CF3CO2D to the reaction mixture simplifies the kinetics to pseudo first-order in [QAc] with k = 4.3 × 10-3 min-1.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 138
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 455-466 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We have studied the kinetics of a reaction in which starting materials A and B react to form the products C and D directly, as well as by way of two additional intermediate reactions. In the first intermediate reaction, A and C react to form D and E, and in the second intermediate reaction, B and E react to form 2C. There are three conservation laws, which effectively reduce the number of variables to two, resulting in nonlinear coupled first order differential equations for [A](t) and [B](t). These equations are readily solved by standard numerical procedures, for various values of the relative reaction rates and starting concentrations. Our results are used to fit experimental data for the case in which A and B are 1-acetyl-4-(1-ethoxycarbonyl-1-cyano)methylene-1,4-dihydroquinoline and water, for which the first and third reverse reactions can be neglected.
    Zusätzliches Material: 12 Ill.
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  • 139
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 140
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 481-487 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetic study of the decarboxylation of aspartic acid has been carried out at various [ninhydrin], [H+] and at different temperature ranging from 60-95°C. The reaction follows an irreversible first-order reaction path under pseudo first-order kinetic conditions. The variation of pseudo first-order rate constant (kobs) with ninhydrin concentration was found to be in agreement with equation 1/kobs = B1 + B2/[Ninhydrin]. One mol of carbondioxide evolved from decarboxylation of α-COOH and second mol of carbondioxide comes from the decarboxylation of β-keto acid which is an intermediate and formed during the course of ninhydrin and aspartic acid reaction. On the basis of the observed data, a possible mechanism has been proposed.
    Zusätzliches Material: 3 Ill.
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  • 141
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 791-802 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Pulsed laser photolysis, time-resolved laser-induced fluorescence experiments have been carried out on the reactions of CN radicals with CH4, C2H6, C2H4, C3H6, and C2H2. They have yielded rate constants for these five reactions at temperatures between 295 and 700 K. The data for the reactions with methane and ethane have been combined with other recent results and fitted to modified Arrhenius expressions, k(T) = A′(298) (T/298)n exp(-θ/T), yielding: for CH4, A′(298) = 7.0 × 10-13 cm3 molecule-1 s-1, n = 2.3, and θ = -16 K; and for C2H6, A′(298) = 5.6 × 10-12 cm3 molecule-1 s-1, n = 1.8, and θ = -500 K. The rate constants for the reactions with C2H4, C3H6, and C2H2 all decrease monotonically with temperature and have been fitted to expressions of the form, k(T) = k(298) (T/298)n with k(298) = 2.5 × 10-10 cm3 molecule-1 s-1, n = -0.24 for CN + C2H4; k(298) = 3.4 × 10-10 cm3 molecule-1 s-1, n = -0.19 for CN + C3H6; and k(298) = 2.9 × 10-10 cm3 molecule-1 s-1, n = -0.53 for CN + C2H2. These reactions almost certainly proceed via addition-elimination yielding an unsaturated cyanide and an H-atom. Our kinetic results for reactions of CN are compared with those for reactions of the same hydrocarbons with other simple free radical species. © John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
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  • 142
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 803-811 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the gas-phase reactions of O3 with a series of alkenes have been investigated at atmospheric pressure (ca. 740 torr) of air and 296 ± 2 K, using a relative rate method in the presence of sufficient n-octane to scavenge any OH radicals generated in these reactions. Relative to k(O3 + propene) = 1.00, the rate constants obtained were: 1-butene, 0.975 ± 0.030; 2-methylpropene, 1.14 ± 0.04; 2-methyl-1,3-butadiene (isoprene), 1.21 ± 0.02; 1,4-cyclohexadiene, 4.75 ± 0.23; cyclohexene, 7.38 ± 0.48; cis-2-butene, 12.8 ± 0.8; trans-2-butene, 21.5 ± 1.5; 2-methyl-2-butene, 42.1 ± 2.8; cyclopentene, 64.9 ± 4.3; and 2,3-dimethyl-2-butene, 123 ± 11. These relative rate constants have been placed on an absolute basis using a rate constant for the reaction of O3 with propene of 1.01 × 10-17 cm3 molecule-1 s-1 at 296 K derived from an analysis of the available literature data. The resulting rate constants then lead to a self-consistent set of room temperature data for the reactions of O3 with these alkenes. © John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
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  • 143
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 144
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 813-837 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Propane oxidation in jet-stirred reactor was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C1—C4 hydrocarbons. The present detailed mechanism is able to reproduce experimental species concentration profiles obtained in our high-pressure jet-stirred reactor (900 ≤ T/K ≤ 1200; 1 ≤ P/atm ≤ 10; 0.15 ≤ φ ≤ 4) and in a turbulent flow reactor at 1 atm; ignition delay times measured in shock tube (1200 ≤ T/K ≤ 1700; 2 ≤ P/atm ≤ 15; 0.125 ≤ φ ≤ 2); H-atoms concentrations measured in shock tube during the pyrolysis of propane and burning velocities of freely propagating premixed propane-air laminar flames. The computed results are discussed in terms of pressure and equivalence ratio (φ) effects on propane oxidation. The same detailed kinetic reaction mechanism can also be used to model the oxidation of methane, ethylene, ethane, and propene in similar conditions. © John Wiley & Sons, Inc.
    Zusätzliches Material: 9 Ill.
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  • 145
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 871-885 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The thermal decomposition of vinylacetylene (C4H4) was studied behind reflected shock waves using both a single-pulse method (reaction time between 0.8 and 3.3 ms) and a time-resolved UV-absorption method (230 nm). The studies were done over the temperature range of 1170-1690 K at the total pressure range of 1.3-2.3 atm. The mechanism was used to interpret both the early and late stages of vinylacetylene decomposition at the high temperatures. It was confirmed that C4H4 dissociation proceeded through the following three channels. The rate constant expression of reaction (1) was determined as k1 = 6.3 × 1013 exp(-87.1 kcal/RT) s-1. The rate constants of the succeeding reactions (chain reaction, C4H4 + H → i-C4H3 + H2 and C4H4 + H → C2H2 + C2H3 and decomposition reactions of free radicals, i-C4H3 + M → C4H2 + H + M) were confirmed or estimated. © John Wiley & Sons, Inc.
    Zusätzliches Material: 9 Ill.
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  • 146
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 79-101 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The OH reaction with isoprene is studied. Methyl nitrite photolysis experiments were carried out in an outdoor smog chamber in an attempt to identify as completely as possible OH-isoprene product distribution. Emphasis was placed on identification and quantification of oxygenated products. A Tenax-based cryo-trap thermal desorber used to trap, concentrate, and dry chamber samples for identification on a GC/MS is described. Analysis of the products revealed that O(3P) can form in reaction systems designed to study OH reactions that include high concentrations of NO, and consequently NO2, hence, this reaction is also examined. The yields of methacrolein and methyl vinyl ketone are determined as 25 ± 3 and 35.5 ± 4%, respectively, with an additional 4 ± 2% as 3-methyl furan, totaling 65 ± 4%. These results, combined with those of previous studies allow 80% of isoprene's products to be explicitly identified, and the general structure of the remaining products to be ascertained. The O(3P) reaction produces 84 ± 8% epoxides, and 8 ± 3% species which result in production of HO2, and subsequently, OH. A heretofore unidentified product of the O(3P) reaction, 2-methyl 2-butenal, is identified. The rate constant of the NO2-isoprene reaction is measured.
    Zusätzliches Material: 10 Ill.
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  • 147
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 199-215 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ethyl tertiary butyl ether (ETBE) is being proposed as an additive for use in reformulated gasolines. In this study, experiments were performed to examine the kinetics and mechanism of the atmospheric removal of ETBE. The kinetics of the reaction of ETBE with OH radicals were examined by using a relative rate technique with the photolysis of methyl nitrite to generate OH radicals. With n-hexane as the reference compound, a value of (9.73 ± 0.33) × 10-12 cm3 molecule-1 s-1 was obtained for the rate constant. The OH rate constant for t-butyl acetate, a product of the oxidation of ETBE, was (4.4 ± 0.4) × 10-13 cm3 molecule-1 s-1 at 298 K.The primary products and molar yields for the OH reaction with ETBE in the presence of NOx were t-butyl formate (0.64 ± 0.03), t-butyl acetate (0.13 ± 0.01), ethyl acetate (0.043 ± 0.003), acetaldehyde (0.16 ± 0.01), acetone (0.019 ± 0.002), and formaldehyde (0.53 ± 0.04). Under the described reaction conditions, the formation of t-butyl nitrite was also observed. From these molar yields, approximately 98% of the reacted ETBE could be accounted for by paths leading to these products. Chemical mechanisms to explain the formation of these products are presented.
    Zusätzliches Material: 4 Ill.
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  • 148
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 467-480 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Azulene, which is isomeric with naphthalene, was studied to determine whether it behaves like a polycyclic aromatic hydrocarbon or an alkene in its gas-phase reactions with OH and NO3 radicals and O3. Using relative rate methods, rate constants for the reactions of azulene with OH and NO3 radicals and O3 of (2.73 ± 0.56) × 10-10 cm3 molecule-1 s-1, (3.9-1.4+2.0) × 10-10 cm3 molecule-1 s-1, and 〈7 × 10-17 cm3 molecule-1 s-1, respectively, were obtained at 298 ± 2 K. The observation that the NO3 radical reaction did not involve NO2 in the rate determining step indicates that azulene behaves more like an alkene than a polycyclic aromatic hydrocarbon in this reaction. No conclusive evidence for the formation of nitroazulene(s) from either the OH or NO3 radical-initiated reaction of azulene (in the presence of NOx) was obtained.
    Zusätzliches Material: 3 Ill.
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  • 149
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 703-710 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The relative OH reaction rates from the simulated atmospheric oxidation of 4-methyl-2-pentanone, trans-4-octene, and trans-2-heptene have been measured. Reactions were carried out at 297 ± 2 K in 100-liter FEP Teflon®-film bags. The OH radicals were produced from the photolysis of methyl nitrite. The measured rate constants (×1011 cm3 molecule-1 s-1) were as follows: 6.77 ± 0.50 for trans-4-octene, 1.40 ± 0.07 for 4-methyl-2-pentanone, and 6.70 ± 0.23 for trans-2-heptene using an absolute rate constant of 2.63 × 1011 cm3 molecule-1 s-1 for the reaction of OH with propene; the principal reference organic. © John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
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  • 150
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 711-725 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Rate coefficients, k1, for the reaction OH + HONO → H2O + NO2, have been measured over the temperature range 298 to 373 K. The OH radicals were produced by 266 nm laser photolysis of O3 in the presence of a large excess of H2O vapor. The temporal profiles of OH were measured under pseudo-first-order conditions, in an excess of HONO, using time resolved laser induced fluorescence. The measured rate coefficient exhibits a slight negative temperature dependence, with k1 = (2.8 ± 1.3) × 10-12 exp((260 ± 140)/T) cm3 molecule-1 s-1. The measured values of k1 are compared with previous determinations and the atmospheric implications of our findings are discussed.
    Zusätzliches Material: 5 Ill.
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  • 151
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 727-734 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Bunting et al. have suggested that a combined application of Hammett ρ values (or Brønsted exponents) and primary kinetic isotope effects to hydride equivalent transfer reactions involving 1,4-dihydronicotinamides and organic oxidants is capable of revealing whether this transfer occurs in a single step or follows a two step e- + H° transfer mechanism (J.W. Bunting, V.S.F. Chew, G. Chu, N.P. Fitzgerald, A. Gunasekara, and H.T.P. Oh, Bioorg. Chem., 12, 141 (1984)). We have used this approach with respect to the reduction of flavins by 1-substituted 1,4-dihydronicotinamides. Compelling lines of evidence are presented to demonstrate that this reaction follows the single step hydride transfer mechanism. We also present an analysis of the Brønsted exponent and the primary kinetic isotope effect data for the flavin reaction. It is shown that although a simple application of these parameters does indeed favor the two step e- + H° transfer mechanism for flavin reduction, various other empirical data provide conclusive evidence for the single step hydride transfer mechanism. We attribute this discrepancy to the occurrence of nonequilibrium solvation of the transition state. We have considered several mechanistic complexities which could produce seemingly inconsistent Hammett and primary isotope effect values, and have concluded that these complexities must be considered in interpreting the mechanism of a hydride-equivalent transfer reaction from kinetic parameters. © John Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
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  • 152
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Mixtures of 1,1,3,3-tetrafluoroacetone and perfluorodi-n-propyl ketone have been photolyzed together over the temperature range 50° to 200°C, and the disproportionation/combination ratio for n-C3F7 and CF2H radicals has been determined to be Δ(n-C3F7, CF2H) = 0.072 ± 0.003. A reevaluation of existing data on CH3 and CF2H radicals leads to a value of Δ(CH3, CF2H) = 0.35. The large variations in Δ for the reactions of alkyl and perfluoroalkyl radicals with CF2H radicals are discussed. © John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
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  • 153
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 154
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 743-760 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The effects of NO on the decomposition of CH3ONO have been investigated in the temperature range 450-520 K at a constant pressure of 710 torr using He as buffer gas. The measured time-dependent concentration profiles of CH3ONO, NO, N2O, and CH2O can be quantitatively accounted for with a general mechanism consisting of various reactions of CH3O, HNO, and (HNO)2. The results of kinetic modeling with sensitivity analyses indicate that the disappearance rate of CH3ONO is weakly affected by NO addition, whereas that of the HNO intermediate strongly altered by the added NO. In the presence of low NO concentrations, the modeling of N2O yields leads to the rate constant for the bimolecular reaction, HNO + HNO → N2O + H2O (25): \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{25} = 10^{8.93 \pm 0.30}\, \,e^{-1,550 \pm 150/{\rm T}} {\rm cm}^3 /{\rm mol}\,{\rm s} $$\end{document} In the presence of high NO concentrations (PNO 〉 50 torr), the modeling of CH2O yields gives the rate constant for the termolecular radical formation channel, HNO + 2NO → HN2O + NO2 (35): \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{35} = 10^{11.2 \pm 0.3}\, \,e^{-1050 \pm 200/{\rm T}} {\rm cm}^6 /{\rm mol}^2\,{\rm s} $$\end{document} Discussion on the mechanisms for reactions (25) and (35), and the alkyl homolog of (35), RNO + 2NO, is presented herein. © John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
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  • 155
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 781-790 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The thermal unimolecular decomposition of hex-1-ene-3-yne (HEY) has been investigated over the temperature range 949-1230 K using the technique of very low-pressure pyrolysis (VLPP). One reaction pathway is the expected C5—C6 bond fission to form the resonance-stabilized 3-ethenylpropargyl radical. There is a concurrent process producing molecular hydrogen which probably occurs via the intermediate formation of hexatrienes and cyclohexa-1,3-diene. RRKM calculations yield the extrapolated high-pressure rate parameters at 1100 K given by the expressions 1016.0±0.3 exp(-300.4 ± 12.6 kJ mol-1/RT) s-1 for bond fission and 1013.2+0.4 exp(-247.7 ± 8.4 kJ mol-1/RT) for the overall formation of hydrogen. The A factors were assigned from the results of previous studies of related alkynes, alkenes, and alkadienes. The activation energy for the bond fission reaction leads to ΔHf300° [H2CCHCCĊH2] = 391.9, DH300° [H2CCHCCCH2—H] = 363.3, and a resonance stabilization energy of 56.9 ± 14.0 kJ mol-1 for the 3-ethenylpropargyl radical, based on a value of 420.2 kJ mol-1 for the primary C—H bond dissociation energy in alkanes. Comparison with the revised value of 46.6 kJ mol-1 for the resonance energy of the unsubstituted propargyl radical indicates that the ethenyl substituent (CH2=CH) on the terminal carbon atom has only a small effect on the propargyl resonance energy. © John Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
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  • 156
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 861-869 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Data from previous articles on the initial polymerization rates of a series of monoalkyl substituted phenyl methacrylates were found to depend strongly on the size and position of the monoalkyl substituent in the phenyl ring. In order to investigate the possibility of correlation of all the rate data obtained, all those for phenyl methacrylate and ten other alkylphenyl substituted methacrylate monomers were fitted into empirical linear free energy relationships (LFER). Assuming steady-state kinetics and separating out the initiator decomposition contribution to the initial overall rate Rp, it was demonstrated that k′ = kp/kt½ can be successfully correlated with LFER equations containing predominantly steric parameters. The steric influence is more pronounced in the o- than in the p-substitution, due to the proximity of the o-substituent to the reaction propagation site. The results are corroborated by the existence of an isokinetic relationship of ΔH
    Zusätzliches Material: 3 Ill.
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  • 157
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 887-894 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The acid-catalyzed hydrolyses of triacetyl-glycerol and of tributyryl-glycerol take place following a simple monoexponential kinetic scheme. The result can be interpreted as all three ester groups reacting with approximately the same specific rate. This observation reported in 1920 is unusual, because the intrinsic reactivities of primary and secondary esters are different, and because as far as the reaction proceeds, the remaining ester groups have neighboring hydroxyl groups, which undoubtly alter the reactivity of the reaction centers, relative to the situation in the initial reactant structure. The phenomenom can be explained by considering that local solvation effects due to neighboring hydrophylic groups remain unchanged as the transition-state complex is formed in all three stages of the reaction. © John Wiley & Sons, Inc.
    Zusätzliches Material: 3 Ill.
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  • 158
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 895-902 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A general expression is derived for the approach to a new equilibrium when a monomer/dimer solution is diluted by a factor of n. The error introduced by a simple exponential treatment is analyzed. The response of a trityl monomer/dimer equilibrium to dilution by a factor of two in a stopped-flow apparatus has been used to measure the rate constant k11. The results fall on the same Eyring plot with those obtained at lower temperatures, by another method, in the early 1930's by Ziegler and co-workers. © John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
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  • 159
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 903-908 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the permanganate-sulfite redox reaction has been studied in the alkaline medium using a stopped-flow technique. In the pH range 10 to 12 the reaction was found to obey the rate expression: -½d[MnO4-]/dt = (k1 + k2[OH-]) [MnO4-] [SO32-]. Mechanisms for the two paths involving the formation of a (O3MnOSO3)3- complex prior to the rate-determining step are consistent with the data. © John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
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  • 160
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 917-917 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 161
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 162
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The pyrolysis kinetics of primary, secondary, and tertiary β-hydroxy ketones have been studied in static seasoned vessels over the pressure range of 21-152 torr and the temperature range of 190°-260°C. These eliminations are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are expressed by the following equations: for 1-hydroxy-3-butanone, log k1(s-1) = (12.18 ± 0.39) - (150.0 ± 3.9) kJ mol-1 (2.303RT)-1; for 4-hydroxy-2-pentanone, log k1(s-1) = (11.64 ± 0.28) - (142.1 ± 2.7) kJ mol-1 (2.303RT)-1; and for 4-hydroxy-4-methyl-2-pentanone, log k1(s-1) = (11.36 ± 0.52) - (133.4 ± 4.9) kJ mol-1 (2.303RT)-1. The acid nature of the hydroxyl hydrogen is not determinant in rate enhancement, but important in assistance during elimination. However, methyl substitution at the hydroxyl carbon causes a small but significant increase in rates and, thus, appears to be the limiting factor in a retroaldol type of mechanism in these decompositions. © John Wiley & Sons, Inc.
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  • 163
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 999-1007 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A detailed kinetic study of the reaction of toluidine blue (tolonium chloride) (TB+ Cl-) with thiourea (TU) in aqueous hydrochloric acid solution is reported. The reaction was first order with respect to toluidine blue and the reductant and second order with respect to [H+]. Thiourea had a 2:1 stoichiometric ratio with TB+. Toluidine blue was reduced to a colorless base in two one-electron reduction steps and TU was oxidized to thioformamidinium ion, which dimerized rapidly to give stable dithioformamidinium ion. The energy parameters obtained for TB+-TU reaction were mean energy of activation (Ea′) = 26.7 ± 2.4 kJ M-1; enthalpy of activation (ΔH#) = 24.2 kJ M-1; frequency factor (A) = 1.04 × 104 M-3 s-1; and entropy of activation (ΔS#) = -176.35 J M-1 s-1. © John Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
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  • 164
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 1023-1034 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the enzymic oxidation of dopamine (A) by polyphenol oxidaze (E) was studied by spectrophotometrically monitoring the concentration of the reaction product, 2,3-dihydroindole-5, 6 quinone, at 470 nm. The kinetics model proposed for the reaction and the effect of pH agreed with the experimental data and the resulting rate equation is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ -\frac{{d[{\rm A}]}}{{dt}} = \frac{{1.5081 \times 10^{-4} [{\rm E}_0][{\rm A]}}}{{1 + 2.0896 \times 10^6 [{\rm H}^{\rm + }]}} $$\end{document} where [A] is the concentration of dopamine (mM), [Eo] the concentration of polyphenol oxidaze (mg/1) and [H+] the concentration of hydrogen ion (M) in the reaction mixture. © John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
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  • 165
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The ultraviolet absorption spectrum and the self reaction kinetics of CF3O2 radicals have been studied in the gas phase at 298 K using the pulse radiolysis technique. Long pathlength Fourier transform infrared (FTIR) spectroscopy was used to identify and quantify reaction products. Absorption cross sections were quantified over the wavelength range 215-270 nm. The measured cross section at 230 nm was; \documentclass{article}\pagestyle{empty}\begin{document}$$ \sigma_{{\rm CF3O2}} (230\,{\rm nm) = (2}{\rm .06} \pm {\rm 0}{\rm .40)}\times {\rm 10}^{{\rm - 18}} {\rm cm}^{\rm 2}\, {\rm molecule}^{{\rm -1}} $$\end{document} Errors represent statistical (2σ) together with our estimate of potential systematic errors. The absorption cross section data were then used to derive the observed self reaction rate constant for reaction (1), defined as -d[CF3O2]/dt = 2k obs[CF3O2]2 klobs = (3.6 ± 0.9) × 10-12 cm3 molecule-1 s-1. The only carbon containing product observed by FTIR spectroscopy was CF3OOOCF3. Consideration of the loss of CF3O2 radicals to form the trioxide CF3OOOCF3 allows derivation of the true bimolecular rate constant for reaction (1); k1 = (1.8 ± 0.5) × 10-12 cm3 molecule-1 s-1. These results are discussed with respect to previous studies of the absorption spectra of peroxy radicals, the kinetics, and mechanisms of their self reaction. © John Wiley & Sons, Inc.
    Zusätzliches Material: 7 Ill.
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  • 166
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 1083-1091 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A study is made of the kinetic salt effects upon the outer-sphere electron transfer reaction between hexacyanoferrate(II) and 4-pyridinecarboxylatopentaamminecobalt(III). The observed salts effects are analyzed, taking into account the possible association of the reactants with the ions of the supporting electrolyte, though no conclusive results could be obtained. A correlation has been established between the logarithm of the observed second-order rate constants and the logarithm of the rate constants for a related innersphere electron transfer reaction. From this correlation the conclusion can be drawn that the observed salt effects in concentrated electrolyte solutions are mainly due to the effects on the electron transfer step. © John Wiley & Sons, Inc.
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  • 167
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 1093-1101 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We studied the kinetics of the N-chlorination of 2-aminobutyric, 3-aminoisobutyric, and 4-aminobutyric acids by sodium hypoclorite in strongly alkaline aqueous solution. As in the case of other amines, the rate of formation of the four N-chloroamino acids was proportional to the concentrations of hypochlorite and amino acid, and inversely proportional to the concentration of hydroxyl ions. A reaction mechanism compatible with these results is proposed and discussed. © John Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
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  • 168
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Data on the tropospheric degradation of proposed substitutes for ozone depleting CFCs were obtained by conducting photochemical oxidation studies of HCFCs and HFCs using long path Fourier transform infrared spectroscopy. The hydrogen abstraction reactions were initiated using Cl radicals rather than OH radicals because of the rather unreactive nature of the compounds. The experimental product yields at T = 25 ± 3°C and 700 Torr of dry air were: CHClF2 (1.11 ± 0.06 C(O)F2); CClFHCF3 (1.00 ± 0.04 CF3C(O)F); CF3CHF2 (1.09 ± 0.05 C(O)F2); CClF2CH3 (0.98 ± 0.03 C(O)F2); CHF2CH3 (1.00 ± 0.05 C(O)F2); CF3CH2F (0.16 ± 0.03 CF3CF(O), and 0.83 ± 0.22 HFC(O)), where all standard deviations are 2σ. For each compound, the critical step in determining the oxidation products was the decomposition of a halogenated alkoxy radical. For HCFC-22 and HCFC-124, the major alkoxy radical decomposition route was Cl elimination. The HFC-125 product data were consistent with C—C cleavage of a two carbon alkoxy radical as the major decomposition route whereas both C—C cleavage and H abstraction by O2 were significant contributors to the decomposition of the HFC-134a alkoxy radical. Secondary Cl reactions in the HCFC-142b and HFC-152a experiments prevented an unambiguous determination of the decomposition modes; the data are consistent with both C—C bond scission and Cl reactions with halogenated aldehydes producing the oxidation product C(O)F2. With the exception of the HFC-134a and HFC-125 data, the proposed mechanisms can account for the major oxidation products. For HFC-134a and HFC-125, a number of product bands could not be identified. The bands are likely due to products from reactions involving the CF3O2 radical. © John Wiley & Sons, Inc.
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  • 169
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 170
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 11-18 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Studies of the stoichiometry and kinetics of the reaction between hydroxylamine and iodine, previously studied in media below pH 3, have been extended to pH 5.5. The stoichiometry over the pH range 3.4-5.5 is 2NH2OH + 2I2 = N2O + 4I- + H2O + 4H+. Since the reaction is first-order in [I2] + [I3-], the specific rate law, k0, is k0 = (k1 + k2/[H+]) {[NH3OH+]0/(1 + Kp[H+])} {1/(1 + KI[I-])}, where [NH3OH+]0 is total initial hydroxylamine concentration, and k1, k2, Kp, and KI are (6.5 ± 0.6) × 105 M-1 s-1, (5.0 ± 0.5) s-1, 1 × 106 M-1, and 725 M-1, respectively. A mechanism taking into account unprotonated hydroxylamine (NH2OH) and molecular iodine (I2) as reactive species, with intermediates NH2OI2-, HNO, NH2O, and I2-, is proposed.
    Zusätzliches Material: 3 Ill.
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  • 171
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A kinetic study of the reactions I- + S2O8= and CV+ + OH- (CV = 4, 4′, 4″-tris(dimethylamino)triphenylmethyl chloride or crystal violet) in different water in oil microemulsions is reported. The dependence of the rate constants on the nature of the surfactant as well as on the molar ratio R = [H2O]/[Surfactant] has been investigated. The results are interpreted on the basis of the electrostatic interactions between the reactants and the surfactant polar heads and considering the water properties inside the aqueous core of the droplets.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 172
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 1-10 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The rate constants for reactions of OH with ClCH2CH2Cl, Cl2CHCHCl2, BrCH2CH2Br, CH3CH2Br have been measured by using a discharge flow-resonance fluorescence (DF-RF) technique over the temperature range 293-418 K. The rate constants as a function of temperature were fitted to the Arrhenius expression as follows: (k's units are 10-12 cm3 molecule-1 s-1, and Ea's units are cal/mol) \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm OH} + {\rm ClCH}_2 {\rm CH}_2 {\rm Cl}:} & {k_1 = (8.91 \pm 1.63)^ \ast {\rm EXP}((-2164.5 \pm 119.9)/RT)}\\[10pt] {{\rm OH} + {\rm BrCH}_2 {\rm CH}_2 {\rm Br}:} & {k_2 = (14.36 \pm 2.70)^ \ast {\rm EXP}((- 2521.4 \pm 123.5)/RT)}\\[10pt] {{\rm OH} + {\rm Cl}_2 {\rm CHCHCl}_2:} & {k_3 = (5.01 \pm 0.89)^ \ast {\rm EXP}((- 1825.8 \pm 116.7)/RT)} \\[10pt] {{\rm OH} + {\rm CH}_3 {\rm CH}_2 {\rm Br}:} & {k_4 = (23.45 \pm 4.62)^ \ast {\rm EXP}((- 2558.2 \pm 124.1)/RT)}\end{array} $$\end{document} The experimental data have been compared with theoretical calculations of the semi-empirical BEBO-transition state method. Life-times of the four haloethanes in the troposphere have been estimated.
    Zusätzliches Material: 5 Ill.
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  • 173
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 31-40 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetic measurements in the Flash Vacuum Thermolysis (FVT) of 3,5-Dimethyl- and 5-Methyl- 4-Nitroisoxazole confirm the already suggested intermediacy of the isomer 2H-Azirine in the formation of 1- Cyano-1-Nitroacetone. Moreover, theoretical calculations of the stabilization energy (Es), at the transition state, using second order perturbation suggest that this azirine is formed through the isomer furoxan rather than directly from the starting isoxazole.
    Zusätzliches Material: 5 Tab.
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  • 174
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 41-49 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The oxidation kinetics of malachite green (MG) with peroxydisulphate ion (PDS) were investigated by monitoring the absorbance change at 618 nm, in aqueous solutions under buffered and unbuffered conditions. Under both conditions, the reaction had first order dependence on reductant and a fractional order (one half) dependence on the oxidant. The stoichiometric ratio between MG and PDS was 1:2. The reaction had a negative salt effect. Reaction rates were enhanced under both high or low pH relative to neutral conditions. A plausible mechanism is proposed.
    Zusätzliches Material: 1 Ill.
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  • 175
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 67-78 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We studied the formation and hydrolysis of the Schiff base of pyridoxal-5′ -phosphate (PLP) and n-dodecylamine (DOD) by kinetic methods and found the formation rate constants to be much larger than those reported for related systems. This can be ascribed to the occurrence of local concentration of charges in the vicinity of the carbinolamine, which stabilizes the corresponding transition state of the dehydration reaction. On the other hand, the hydrolysis rate constants of our system were considerably smaller as a result of the 12-atom hydrocarbon chain acting as a bulky hydrophobic rest protecting the imine bond from attack by water.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 176
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 51-65 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The equilibrium constant, Keq of the reaction NO2 + NO3 + M 2 N2O5 + M has been determined for a small range of temperatures around room temperature in air at 740 torr by direct spectroscopical measurements of NO2, NO3, and N2O5. At 298 K, Keq was determined as (3.73 ± 0.61) × 10-11 cm3 molecule-1. Averaging this and 11 other independent evaluations of Keq yields Keq = (3.31 ± 0.82) × 10-11 cm3 molecule-1, where the uncertainty is given as one standard deviation. The kinetics of the O3/NO2/N2O5/NO3/ air system was studied in a static chamber at room temperature and 740 torr total pressure. Evidence of a unimolecular decay reaction of NO3, NO3 → NO + O2, was found and its rate coefficient was estimated as (1.6 ± 0.7) × 10-3 s-1 at 295 ± 2 K.
    Zusätzliches Material: 4 Ill.
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  • 177
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 178
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 191-198 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the reactions of hydroxy radicals with cyclopropane and cyclobutane has been investigated in the temperature range of 298-492 K with laser flash photolysis/resonance fluorescence technique. The temperature dependence of the rate constants is given by k1 = (1.17 ± 0.15) × 10-16 T3/2 exp[-(1037 ± 87) kcal mol-1/RT] cm3 molecule-1 s1 and k2 = (5.06 ± 0.57) × 10-16 T3/2 exp[-(228 ± 78) kcal mol-1/RT] cm3 molecule-1 s-1 for the reactions OH + cyclopropane → products (1) and OH + cyclobutane → products (2), respectively. Kinetic data available for OH + cycloalkane reactions were analyzed in terms of structure-reactivity correlations involving kinetic and energetic parameters.
    Zusätzliches Material: 5 Ill.
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  • 179
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 180
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 217-237 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The literature on the pyrolysis of acetylene below 1000 K is reviewed and it is shown that the reaction is a radical chain polymerization initiated by H atoms. The induction period is examined and shown to arise from a rapid autocatalysis produced by the very first product, vinyl acetylene. Data from studies of acetylene polymerization induced by vinyl acetylene and styrene are examined and shown to be in good qualitative agreement with the radical chain process presented. Measured and where needed, estimated rate constants are given to produce numerical estimates of chain length, rates of polymerization, induction period, and rates of initiation. It is further shown that all the products of the polymerization are capable of efficiently initiating chains in the system. An examination of the possible kinetics of vinylidene shows that it does not play any role in acetylene chemistry.
    Zusätzliches Material: 1 Tab.
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  • 181
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The present study examines the kinetics and mechanism of the formation of [Zn(CN)4]2- from ZnR22- (R represents 4-(2-Pyridylazo)resorcinol, short named as Par) and vice versa. The reactions have been followed at 494 nm (λmax of [Zn(Par)2]2-, ε = 7.8 × 104 M-1 cm-1) using stopped-flow spectrophotometer in presence of excess of incoming ligand. The data show that the formation of [Zn(CN)4]2- complex is first order in [ZnR22-] and the order with respect to [CN-] varies from one at higher cyanide concentration to zero at low [CN-]. These observations suggest a slow dissociation of [ZnR2]2- to ZnR and R2- and a cyanide assisted rapid dissociation of [ZnR2]2- to [ZnR(CN)x]x- followed by their rapid conversion to [Zn(CN)4]2-. The reaction of Zn(Par) with cyanide ions also follow first order kinetics at higher as well as lower cyanide concentrations. The reverse reaction exhibits first order dependence each in [Zn(CN)42-] and [Par2-], but an inverse first order dependence in [CN-] at low Par concentrations. However, at higher Par concentration the reaction rate tends to be independent of [Par2-]. On the basis of forward and reverse rate studies, a five step mechanism consistent with these results has been proposed. The activation parameters and the effect of ionic strength have been used in further support to the proposed mechanism. The effect of pH on the rates of forward and reverse reaction has also been investigated.
    Zusätzliches Material: 6 Ill.
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  • 182
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 271-278 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction between H and C3H5 has been studied at 291 K. Exciplex laser flash photolysis at 193.3 nm of hexa-1,5-diene-He mixtures generated both H and C3H5 ([H] ≪ [C3H5]), which were detected in time-resolved mode by resonance fluorescence and absorption spectroscopy, respectively. Rate coefficients are presented at four pressures in the range 98 ≤ P/torr ≤ 400; no clear pressure-dependence is found in this range of pressures and the mean rate coefficient is (2.8 ± 1.0) × 10-10 cm3 molecule-1 s-1. Calculations based on the Troe factorization method confirm that this reaction is near its high-pressure limit under the experimental conditions.
    Zusätzliches Material: 1 Ill.
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  • 183
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 255-269 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The effect of CFCl3 (0.025-0.200 mbar) addition on the formation of ozone in 214 nm photolysis of oxygen (800-2000 mbar) was investigated. Kinetic analysis of the drastic reduction in ozone formation in the presence of CFCl3 shows that it proceeds by a chain mechanism with a chain length of 5.07 ± 0.21(2σ). This chain length is independent of CFCl3 and O2 pressures as well as incident light intensity and the mechanism of the chain reaction is governed by the Cl generating reactions of ClO radicals. A mechanism based only on the self reaction of these radicals: ClO + ClO → Cl2 + O2 (7), Cl + ClO2 (8), and Cl + OClO (9), followed by fast decomposition of ClO2 into Cl and O2, predicts a chain length which is considerably lower than the observed value. Incorporation of the reaction CFCl2O2 + ClO → CFCl2O + ClO2 (11) in the mechanism satisfactorily accounts for the observed chain length. A lower limit of 3 × 10-12 cm3 molecule-1 s-1 for k11 is estimated.
    Zusätzliches Material: 5 Ill.
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  • 184
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 185
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 279-295 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Reactions of atomic oxygen with isocyanic acid (HNCO) have been studied in incident and reflected shock wave experiments using HNCO/N2O/Ar mixtures. Quantitative time-histories of the NH(X3Σ-) and OH(X2Πi) radicals were measured behind the shock waves using cw, narrow-linewidth laser absorption at 336 nm and 307 nm, respectively. The second-order rate coefficients of the reactions: and were determined from early-time NH and OH formation rates, with least-squares two-parameter fits of the results given by: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {k_{2a} = 1.9 \times 10^{13} \exp (-7150/T,{\rm K})} & {{\rm (}f = 0.62,{\rm F} = 1.52{\rm)}} & {T = 2120-2500{\rm K}}\end{array} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {k_{2c} = 1.4 \times 10^{14} \exp (- 10300/T,{\rm K})} & {{\rm (}f = 0.65,{\rm F} = 1.35{\rm)}} & {T = 2120 - 3190{\rm K}},\end{array} $$\end{document} cm3 mol-1 s-1. The minimum and maximum rate constant factors (ƒ,F) define the lower and upper uncertainty limits, respectively.An upper limit on the rate coefficient of was determined to be: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {k_3 \le 1.5 \times 10^{12} {\rm cm}^3 {\rm mol}^{- 1} {\rm s}^{- 1},} & {T = 2120 - 2350{\rm K}}\end{array} $$\end{document} .
    Zusätzliches Material: 9 Ill.
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  • 186
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 297-307 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The rate coefficients of thermal decomposition of peroxyacetic nitric anhydride (PAN) and peroxymethacrylic nitric anhydride (MPAN) were measured over the temperature range 302-323 K. The resulting Arrhenius expressions were k = 1017.4±0.4 exp(-28.5 ± 0.5/RT) for PAN, and k = 1016.2±0.7 exp(-26.8 ± 1.0/RT) for MPAN, where the activation energy is in Kcal/mol. These results are in good agreement with previous studies of PAN and other PAN-type compounds, and imply that energies of RC(O)OO—NO2 bonds are relatively independent of the nature of R.
    Zusätzliches Material: 4 Ill.
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  • 187
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 489-516 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Previously measured decay rates of HNO in the presence of NO have been kinetically modeled on the basis of thermochemical data calculated with the BAC-MP4 technique. The results of this modeling, aided by TST-RRKM calculations for the association of HNO and the isomerization, decomposition, and stabilization of the many dimers of HNO, reveal that the decay of HNO under NO-lean conditions occurs primarily by association forming cis- and trans-(HNO)2 at temperatures below 420 K. N2O, which is a relatively minor product, is believed to be formed by H2O elimination from cis-HON = NOH, a product of succesive isomerization reactions: trans-(HNO)2† → HN(OH)NO† → HN(O)NOH† → cis-HON NOH†. The calculated rate constants, which fit experimental data quantitatively, can be represented by k = 1016.2 × T-2.40e-590/T cm3/mol sec for the HNO recombination reaction and k = 10-2.44T3.98e-600/T cm3/mol sec for N2O formation in the temperature range 80-420 K, at a total pressure of 710 torr H2 or He.Under NO-rich conditions, HNO reacts predominantly by the exothermic termolecular reaction, HNO + 2NO → HN(NO)ONO → HN NO + NO2, with a rate contant of (6 ± 1) × 109 cm6/mol2 sec at room temperature, based on both HNO decay and NO2 production. All existing thermal kinetic data on HNO + HNO and HNO + 2NO processes can be satisfactorily rationalized with a unified model based on the thermochemical data obtained by BAC-MP4 calculations.
    Zusätzliches Material: 13 Ill.
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  • 188
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 631-638 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: N-t-butylaniline, N-t-butyl-p-anisidine, and N-t-butyl-p-nitroaniline have been pyrolyzed in a stirred-flow reactor at 510-620°C, 8-15 torr total pressure, and 0.5-1.5 s contact time, using toluene as carrier gas. An order one kinetics was observed for the consumption of the amines. The reactions yielded 95 ± 2% isobutene plus the corresponding anilines as reaction products. The rate coefficients followed the Arrhenius equations N-t-butylaniline \documentclass{article}\pagestyle{empty}\begin{document}$$ k = 10^{14.19 \pm 0.32} \exp (- 234 \pm 5\,{\rm kJ/mol}\, RT) $$\end{document} N-t-butyl-p-anisidine \documentclass{article}\pagestyle{empty}\begin{document}$$ k = 10^{13.05 \pm 0.23} \exp (- 208 \pm 4\,{\rm kJ/mol}\, RT) $$\end{document} N-t-butyl-p-nitroaniline \documentclass{article}\pagestyle{empty}\begin{document}$$ k = 10^{13.73 \pm 0.28} \exp (- 235 \pm 6\,{\rm kJ/mol}\, RT) $$\end{document}The results are consistent with an unimolecular elimination of isobutene involving polar four-center cyclic transition states. © John Wiley & Sons, Inc.
    Zusätzliches Material: 3 Ill.
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  • 189
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 639-648 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A relative rate method has been used to determine rate constants for the gas-phase reactions of a series of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) at 298 ± 2 K and atmospheric pressure of air. Based on a rate constant for the reaction of the Cl atom with CH4 of (1.0 ± 0.2) - 10-13 cm3 molecule-1 s-1 at 298 K, the following Cl atom reaction rate constants (in units of 10-15 cm3 molecule-1 s-1) were obtained: CH3F, 340 ± 70; CH3CHF2, 240 ± 50; CH2FCl, 110 ± 25; CHFCl2, 21 ± 4; CHCl2CF3, 14 ± 3; CHFClCF3, 2.7 ± 0.6; CH3CFCl2, 2.4 ± 0.5; CHF2Cl, 2.0 ± 0.4; CH2FCF3, 1.6 ± 0.3; CH3CF2Cl, 0.37 ± 0.08; and CHF2CF3, 0.24 ± 0.05. These Cl atom reaction rate constants are compared with literature data and with the corresponding OH radical reaction rate constants. © John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
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  • 190
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 665-670 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the reaction (1) obey the rate law (2) in acetate buffered solutions. A comparison with H2O2 and S2O82- shows the reactivity order to be H2O2 〈 HSO5- 〉 S2O82-. © John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
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  • 191
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 649-663 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The ultraviolet absorption spectrum of the neopentyl peroxy radical (CH3)3CCH2O2, and the kinetics and products of its self reaction have been studied in the gas phase at 298 K. Absorption cross sections were quantified over the wavelength range 230-290 nm. The measured cross section at 250 nm was; \documentclass{article}\pagestyle{empty}\begin{document}$$ \sigma ({\rm CH}_3)_3 {\rm CCH}_2 {\rm O}_{2(250\,{\rm nm})} = (5.4 \pm 1.2) \times 10^{-18} {\rm cm\, molecule}^{-1} $$\end{document} Errors represent statistical (2σ) together with our estimate of potential systematic errors(15%). The kinetics of the decay of the UV absorption following the generation of the neopentyl peroxy radicals was complicated by the rapid decomposition of the (CH3)3CCH2O radicals formed in channel (4a). By measuring the yield of t-butyl peroxy radicals, the branching ratio k4a/(k4a + k4b) was determined to be 0.39 ± 0.03. The rate constant for the self reaction of neopentyl peroxy radicals was k4 = (1.07 ± 0.22) × 10-12 cm3 molecule-1 s-1. Quoted errors represent 2σ. These results are discussed with respect to the available literature data. © John Wiley & Sons, Inc.
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  • 192
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992) 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 193
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 671-677 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Numerical integrations of a hypothetical radical chain reaction model have been performed for the pyrolysis of CH2ClCH3 which is known to be molecular. Analyses of the modelling results have led to a better understanding of the participation (or nonparticipation) of “dead” radicals in the self-inhibition of the radical chain reaction. Attention is focused on the fact that apparently slow elementary reactions still may have to be taken into account in a pyrolysis mechanism when they produce “dead” radicals which can accumulate. © John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 194
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 689-693 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reduction of methyl viologen (MV2+) and 9,10-anthraquinone-2-sulfonate (AQS) by the benzopinacol anion in 50% (v/v) propan-2-ol/water was investigated spectroscopically. The rate constants for these reactions were found to be 12.9 ± 0.2 and 0.23 ± 0.01 M-1 s-1, respectively. © John Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 195
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 679-687 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of the gas-phase reaction between NO2 and trichloroethene has been investigated in the temperature range 303-362.2 K. The pressure of NO2 was varied betwen 5.1 and 48.7 torr and that of trichloroethene between 7.3 and 69.5 torr. The reaction was homogeneous. Two products were formed: nitrosyl chloride, ClNO, and glyoxyloxyl chloride, HC[O]C[O]Cl, which was identified by its infrared spectrum and its molecular weight determined by chromatography. The rate of consumption of the reactants was independent of the total pressure and can be represented by a second-order reaction: \documentclass{article}\pagestyle{empty}\begin{document}$$ -d[{\rm NO}_2]/dt = - 2d[{\rm CHClCCl}_2]/dt = k[{\rm NO}_2][{\rm CHClCCl}_2] $$\end{document} The following mechanism was proposed to explain the experimental results: The following expression was obtained for k: \documentclass{article}\pagestyle{empty}\begin{document}$$ k= 2k_1 k_3/[k_2 + k_3] = 4.07 \pm 1.2 \,\times\, 10^2 \exp [-8800\, \pm\, 800\,{\rm cal\,mol}^{-1}/ RT]1\,{\rm mol}^{-1}\,{\rm s}^{-1} $$\end{document}. © John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 196
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 695-701 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Rates of hydrolysis of a series of hydroxamic acids in aqueous acetonitrile, with perfluorooctanoic acid serving as a reactive counterion surfactant, have been determined. The pseudophase ion exchange model satisfactorily explains the surfactant effects. Variation in the structure of the hydrophobic moiety of the hydroxamic acid substrates was obtained by the incorporation of different chain lengths and differently substituted aryl groups into the substrate. The major influence of the change in substrate structure is on the binding constant for binding of the substrate to the surfactant aggregate. The number of substitutions on the aryl ring appears to be more important than the total number of carbon atoms in the substrate. © John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 197
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 761-780 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The thermal decomposition of propene behind reflected shock waves with 1200 〈 T5 〈 1800 K and 1.6 × 10-5 〈 ρ5 〈 2.7 × 10-5 mol/cm3 was studied by IR laser kinetic absorption spectroscopy and gas-chromatographic analysis of reaction products. The present data together with earlier shock tube data were satisfactorily modeled with a 51-reaction mechanism. As the initial step of the reaction, three channels, C3H6 = CH3 + C2H3 (1), C3H6 = H + AC3H5 (2), and C3H6 = CH4 + C2H2 (3), were necessary to interpret all the experimental data. © John Wiley & Sons, Inc.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 198
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 851-859 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The rate of nucleophilic substitution at the phosphorus centre of dialkyl methylphosphonates by methoxide and ethoxide has been studied to investigate the possible involvement of hexacoordinated phosphorus species in this reaction. For alkoxide concentrations less than ca. 1.5 M the rate increases with the square of alkoxide concentration. However, consideration of the activity of the alkoxides, represented by an appropriate acidity function, reveals that only one equivalent of alkoxide is involved in the rate-determining step. Thus, there is no requirement to invoke the intermediacy of a hexacoordinated species in the reaction pathway. © John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 199
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 839-850 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A 480 L evacuable reaction chamber, equipped with FT-IR spectroscopy on-line and ion chromatography off-line, has been used to study the gas phase reaction between the nitrate radical, NO3, and the reduced organic sulphur compounds CH3CH2SH, (CH3CH2)2S, (CH3CH2)2S2, and CH3CH2SCH3 in air. The products CH3CH2SO3H, SO2, H2SO4, CH3CHO, and CH3CH2ONO2 were identified and quantified in the reactions of the first three compounds, CH3CH2SH, (CH3CH2)2S, and (CH3CH2)2S2. The reaction products were CH3CH2SO3H, CH3SO3H, SO2, H2SO4, CH3CHO, and CH2O in the reaction of CH3CH2SCH3. On the basis of identified reaction products and intermediates observed in the infrared spectra, mechanisms are proposed for the reactions between the NO3 radical and the four reduced organic sulphur compounds. The results of this study, together with those from previous experiments performed in this laboratory on CH3SCH3, CH3SH, and CH3SSCH3 lead to the conclusion that all these species, in the reaction with the NO3 radical, follow a similar degradation mechanism producing SO2, H2SO4, R—SO3H, R—CHO, and R—CH2ONO2, as the main reaction products. The inital step of the reaction of NO3 with R—S—R and R—S—H type (R = CH3, CH2CH3) reduced organic sulphur compounds was found to be H-atom abstraction, probably after the formation of an initial adduct. For the reaction between NO3 and R—S—S—R type compounds, evidence for an addition-decomposition reaction, as the initial steps, was obtained. R—S·, R—S(O)·, and R—S(O)2· appear to be formed as intermediates in all the reactions. © John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 200
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 24 (1992), S. 933-941 
    ISSN: 0538-8066
    Schlagwort(e): Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The kinetics of oxidation of tetrahydrofurfuryl alcohol by dihydroxydiperiodatonickelate (IV) complex in the temperature range of 20-35°C has been studied by spectrophotometry in aqueous alkaline medium. The reaction order in [Ni(IV)] was found to be unity and that in [alcohol] to be 1.64-1.69. The rate of oxidation increases with increase in [OH-] and decreases with increase in [IO4-], indicating that dihydroxymonoperiodatonickelate (IV) complex is the reactive species of oxidant. Salt effect studies indicated that the reaction is of ion-dipole type. Under the protection of nitrogen the reaction system does not induce polymerization of acrylonitrile or acrylamide, which indicates that a one-step two-electron transfer mechanism without free radical intermediate may be in operation. A mechanism involving a preequilibrium of an adduct formation between Ni(IV) and alcohol has been proposed. All the experimental phenomena can be explained by the equation derived from the mechanism. The activation parameters of the rate-determining step have been calculated. © John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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