摘要:

AbstractThe 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−1s−1, respectively. © John

ISSN:0538-8066    

DOI:10.1002/kin.550240802

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractRates 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

ISSN:0538-8066    

DOI:10.1002/kin.550240803

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe relative OH reaction rates from the simulated atmospheric oxidation of 4‐methyl‐2‐pentanone,trans‐4‐octene, andtrans‐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 (×1011cm3molecule−1s−1) were as follows: 6.77 ± 0.50 fortrans‐4‐octene, 1.40 ± 0.07 for 4‐methyl‐2‐pentanone, and 6.70 ± 0.23 fortrans‐2‐heptene using an absolute rate constant of 2.63 × 1011cm3molecule−1s−1for the reaction of OH with propene; the princ

ISSN:0538-8066    

DOI:10.1002/kin.550240804

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractRate 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 O3in 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, withk1= (2.8 ± 1.3) × 10−12exp((260 ± 140)/T) cm3molecule−1s−1. The measured values ofk1are compared with previous determinations and the atmospheric implications of our findings

ISSN:0538-8066    

DOI:10.1002/kin.550240805

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractBunting 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. © Joh

ISSN:0538-8066    

DOI:10.1002/kin.550240806

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractMixtures 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 forn‐C3F7and CF2H radicals has been determined to be Δ(n‐C3F7, CF2H) = 0.072 ± 0.003. A reevaluation of existing data on CH3and 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

ISSN:0538-8066    

DOI:10.1002/kin.550240807

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe 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&S

ISSN:0538-8066    

DOI:10.1002/kin.550240808

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550240801

出版商:John Wiley&Sons, Inc.    

年代:1992

数据来源: WILEY