摘要:

AbstractA kinetic investigation is described of the reaction of ground state atomic carbon, C(2p2(3PJ)), monitored by time‐resolved atomic resonance absorption spectroscopy, with a wide range of halogenated olefins and aromatic compounds. Atomic carbon was generated by the repetitive pulsed irradiation (λ>ca. 160 nm) of C3O2in the presence of excess helium buffer gas and the added reactant gases in a slow flow system, kinetically equivalent to a static system. C(23PJ) was then monitored photoelectrically by time‐resolved atomic resonance absorption in the vacuum ultra‐violet (λ = 166 nm, 33PJ← 23PJ) with direct computer interfacing for data capture and analysis. The following absolute second‐order rate constants for the reactions of C(23PJ) with the following reactants are reported:TextReactantkR/cm3molecule−1s−1(300 K)C2F4(1.9 ± 0.1) × 10−10C2Cl4(10.6 ± 0.5) × 10−10CH2CF2(4.3 ± 0.2) × 10−10CHClCCl2(7.9 ± 0.4) × 10−10C6H6(4.8 ± 0.3) × 10−10C6F6(4.9 ± 0.3) × 10−10C6HF5(5.0 ± 0.3) × 10−10C6H2F4(4.4 ± 0.2) × 10−10C6H5—CH3(5.5 ± 0.3) × 10−10C6F5—CF3(5.4 ± 0.3) × 10−10These results, constituting the first reported body of absolute rate data for reactions of ground state carbon with these reactants, are compared with the analogous body of absolute rate data for atomic silicon in its Si(3p2(3PJ)) ground state, also determined hitherto by time‐resolved atomic resonance absorption spectroscopy and demons

ISSN:0538-8066    

DOI:10.1002/kin.550250602

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractNinhydrin has been found to react with Cu(glycine)+and Cu(alanine)+in the ratio of 1:1. The kinetic studies of the reaction were carried out at different concentrations of the reactants at 80°C (pH = 5.0). The reaction proceeds through the formation of a ternary labile complex of ninhydrin with Cu(II) complexes of glycine and alanine. The kinetics were found to follow pseudo‐first‐order reaction path with respect to Cu(II)‐complex in presence of excess [Ninhydrin]. Formation of a ternary labile complex indicates a template reaction mechanism based on the reactions with coordinated ligands. The variation of pseudo‐first‐order rate constants with [ninhydrin]was found to be in good agreement with equation\documentclass{article}\pagestyle{empty}\begin{document}$$ 1/k_{obs} = \frac{{B1}}{{[{\rm Ninhydrin}]}} + B_2 $$\end{document}whereB1andB2are the unknown empirical parameters. The [acetate ion] has no significant effect on the rate constants. On the basis of observed data a probable mechanism has been proposed. © 1993 John Wile

ISSN:0538-8066    

DOI:10.1002/kin.550250603

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractRate constants for several reactions of inorganic radicals with inorganic anions in aqueous and aqueous/acetonitrile solutions have been measured as a function of temperature by laser flash photolysis. The reactions studied were (1) Cl2−+ N3−, (2) Br2−+ N3−, (3) Cl2−+ SCN−, (4) Br2−+ SCN−, (5) SO4−+ Cl−, (6) SO4−+ CO32−, and (7) N3− + I−. The rate constants were corrected for ionic strength and ranged from 106to 109L mol−1s−1. The Arrhenius activation energies varied from 2 to 12 kJ mol−1for the first 4 reactions, were higher for reaction 6, and negative for reaction 5. The pre‐exponential factors also varied considerably with logAranging from 5 to 14. The values ofk298decreased in most cases by more than an order of magnitude upon increasing the acetonitrile (ACN) fraction from 0 to 70%. For most reactions, this decrease ink298was due to changes in logAwith little regularity in the small changes observed inEa. For reaction 7,k298was practically unchanged due to compensating effects of the changes inEaand logAwith ACN mol fraction, giving an isokinetic relationship. An isokinetic relationship was also observed in the case of reaction 6;Eaand logAchange in parallel while changing ACN mol fraction. Reaction 3 (Cl2−+ SCN−) was also studied in water/t‐butanol and water/acetic acid mixtures. Linear correlation was found between log k and the dielectric constant of the medium for water/ACN and water/t‐BuOH but the lines for the two solvent mixtures had different slopes, suggesting specific solvation effects in addition to the primary solvent polarity effects. With water/acetic acid,kdecreased and then increased upon addition

ISSN:0538-8066    

DOI:10.1002/kin.550250604

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA large number of substrates have hitherto been employed in the Belousov‐Zhabotinsky (B‐Z) oscillatory system in pure aqueous medium. A systematic study of aromatic bromate oscillators is limited by solubility problem relating to the compounds and the brominated derivatives. The use of aqueous‐organic mixed media for the oscillatory study is found to be highly useful for the study of water insoluble substances. A comparative study of the oscillatory behavior of gallic acid as substrate in pure aqueous as well as in a number of mixed media have been made in order to ascertain the suitability of mixed media in oscillatory systems. The alteration of oscillatory characteristics in the presence of organic solvent can be understood in terms of the Field‐Koros‐Noyes (FKN) mechanism. The oscillatory behavior of seventeen new substrates in the ferroin‐catalyzed bromate system in 20% (v) acetonitrile is also presented and discussed in this communication. The reactivity of structurally related substrates has been correlated to the structure in terms of the relevant oscillatory parameters. The use of aqueous‐organic mixed media in oscillatory systems would enable the investigation of new classes of substrates since getting them into the solution phase would no longer be a limitation. © 1993 John W

ISSN:0538-8066    

DOI:10.1002/kin.550250605

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe substitution reaction between aquopentacyanoferrate(II) and tetraamminepirazynecarboxylatocobalt(III) to form a binuclear species is studied in various binary aqueous mixtures at different temperatures. Values of activation parameters seem to indicate no change in the mechanism of the reaction in the different mixtures. Medium effects have been rationalized by using a multiparameter regression of solvent parameters. Results show that the reaction follows a dissociative mechanism. © 1993 John Wiley&Sons, Inc

ISSN:0538-8066    

DOI:10.1002/kin.550250606

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe rate coefficients for the removal of O(1D) by reaction with the following seven bromocarbons were measured using time‐resolved vacuum UV atomic resonance fluorescence detection of O(3P): CH3Br, CH2Br2, CHBr3, CF3Br (Halon‐1301), CF2Br2(Halon‐1202), CF2ClBr (Halon‐1211), and CF2BrCF2Br (Halon‐2402). The branching ratios for the quenching of O(1D) to O(3P) by the above molecules were also determined. From these measurements, the rate coefficients for reactive and nonreactive loss of O(1D) were calculated. These results are discussed in terms of their atmospheric relevance and trends in reactivity of O(1D) with hydrocarbons upon halogen substitution. © 1993 John Wiley

ISSN:0538-8066    

DOI:10.1002/kin.550250607

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractOne unit of S(IV) (SO2or SHO3−) is oxidized per 2 units of [NiIII(cyclam)] species to obtain sulfate. Kinetic analyses have been done by varying the acidities (0.013 ⩽ [H+] ⩽ 1.0 M) and halide concentrations (0.000 ⩽ [X−] ⩽ 0.012M;X=Cl and Br) at constant ionic strength (μ = 1.0M). The rate law that incorporates the [X−] and [H+] dependence is −d[NiIII]T/dt=2k[NiIII]T[S(IV)]Twhere 2k={ka[H+] +kbK+k cXK′X[H+] [X−] +k dXK′XK[X−]} {[H+] +K}−1{1 +K′X[X−]}−1, hereka=87 ± 7M−1s−1,kb=(2.5 ± 0.5)×103M−1s−1andpK= 1.8 ± 0.2. Rate constantskaandkbare attributed to the reactions of [NiIII(cyclam) (H2O)2]3+with SO2and SHO3−, respectively. Monohalo species apparent equilibrium constantsK′Cl=(1600 ± 400)M−1andK′Br=(190 ± 20)M−1and rate constantsk cCl=80 ± 8M−1s−1andk cBr= 140 ± 15M−1s−1are ascribed to the protonated pathway, involving the [NiIII(cyclam) (H2O)X]2+and SO2(aq)reaction pairs. The other two rate constants ofk dCl=(5 ± 1)×103M−1s−1andk dBr=(3.1 ± 0.5)×104M−1s−1, refer to the deprotonated pathway and are assigned to the [NiIII(cyclam) (H2O)X]2+/SHO3−redox couple. A deuterium H2O /D2O isotope effect of 2.1–2.8 can be attributed partially to an equilibrium isotope effect at low acidity though a small kinetic isotope (2.5 ± 0.5) effect is evident for the dihydrogen sulfito pathway,ka. The kinetic isotope effect and the absence of sulfite radical scavenging effects are explained by a mechanism entailing migration of a hydride from sulfur to the NiIIIcenter to pro

ISSN:0538-8066    

DOI:10.1002/kin.550250608

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550250601

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY