摘要:

AbstractFlash photolysis technique has been used to obtain the rate and thermodynamic parameters of the reversible dimerization reactions of a range of ten phenoxy radicals (I–X) in a toluene–dibutylphthalate mixture (0.6 cP ≤η≤18.4 cP):\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm R}^{.} + {\rm R}^{.} {\mathop{{\buildrel{-\!\!\longrightarrow}\over{\longleftarrow}}}\limits_{k_{-1}}^{k_1}}{\rm D} $$\end{document}The main reason for the difference in thek1values are the different steric hindrances in radicals. It has been found that the values ofk1for 2,6‐diphenyl‐4‐methoxy‐ (I), 2‐phenyl‐(III), and 2‐methoxyphenoxy (IV) radicals are 3–5 times smaller than the respective diffusion constants calculated according to the Debye formula with regard to the spin‐statistical factor:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{diff} = \sigma \frac{{8{\rm RT}}}{{3000{\rm \eta }}} $$\end{document}The resultant ΔH1≠values for these radicals in toluene and dibutylphthalate are close to the activation energies of the viscous flow of the solventsB. Linear relationships with a slope equal to unity are observed between logk1and log(T/η). The recombination of radicals I, III, and IV is limited by translational diffusion. Thek1values for 2,6‐diphenyl‐ (VII), 2,6‐di‐tert‐butyl‐ (IX), and 2,6‐di‐tert‐butyl‐4‐methylphenoxy (X) radicals are 10–60 times smaller thankdiffand ΔH≠B. In the case of radical X in toluene ΔH1≠0. The recombination of these three radicals includes an intermediate step of complex formation:\documentclass{article}\pagestyle{empty}\begin{document}$${{\rm R}^\cdot+{\rm R}^\cdot}{\mathop {{\scriptstyle\longleftarrow}^{\hskip-13pt\longrightarrow}}}{\rm R^\cdot}\ldots {\rm R}^\cdot \rightarrow {\rm D}$$ \end{document}For 4‐phenyl‐ (II), 2,6‐ dimethoxy‐ (V), 2,4‐diphenyl‐ (VI), and radicals VII, IX, and X the linear relationships between logk1and log (T/η) have a slope of from 0.5 ± 0.05 to 0.8 ± 0.05. Thek1‐1versus η relationships for these radicals are not straight lines. The recombination of these six radicals is limited by translational and rotational diffusion. With the aid of theoretical models, thek1versus η relationships have been used to derive the steric factorfin radical recombination and the angle θ between the axis and the solid angle generatrix. The solid angle defines the reaction spot on the radical‐sphere surface. The recombination of the 2,6‐diphenyl‐4‐diphenylmethylphenoxy radical (VIII) takes place in the region intermediate between the diffusion and the kinetic ones, and the relationship between logk1and log (T/η) for this radical has a plateau portion. The logk‐1versus log (T/η) relationships have precisely the same form as the correspondingk1relationships, which

ISSN:0538-8066    

DOI:10.1002/kin.550120302

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA detailed investigation of the mechanism of cyanogen oxidation is presented. Recent induction time measurements of ignition in cyanogen–oxygen–argon mixtures behind reflected shocks are computer modeled to obtain an agreement between the experimental and calculated values. A 15‐step reaction scheme is suggested to reproduce the parametersEand βiin the experimental parametric relation: τ = 10αexp(E/RT)IICiβi. An explanation is offered to the very strong dependence of the induction time on the cyanogen concentration and the very weak dependence on the oxygen concentration. The sensitivity spectrum shows that the induction time is highly dependent on the O + C2N2→ NCO + CN and NCO + M → N + CO + M reactions (shortened) and the O + NCO → CO + NO and N + NCO → N2+ CO reac

ISSN:0538-8066    

DOI:10.1002/kin.550120303

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractData on the liquid‐phase oxidation of isobutane at 50 and 100°C have been reexamined, using a modified mechanism to take into account the termination by isobutylperoxy radicals. Algebraic expressions are derived from steady‐state methods. Using Arrhenius parameters fitted by transition‐stateAfactors and activation energies derived from observed “best” rate constants, new sets of parameters are derived for the rate constants for propagation bytBuO2+tBuH →t‐BuO2H +tBu⋅:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_4 \, = \,1 \times 10^{8 - 14.5/{\rm \theta }} {\rm M}^{{\rm - 1}} \sec ^{ - 1} $$\end{document}where θ = 2.303RTin kcal/mol. This, together with new values for the termination parameters and rates ofi‐butyl production byk4B, is shown to give good agreement with the published data. An important reaction:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm R}'{\rm O}_{2}^{.} + {\rm RO}_{2} {\rm H}\mathop{{\buildrel{-\!\!\longrightarrow}\over{\longleftarrow}}}\limits^{{\rm 12}}{\rm R'O}_{\rm 2} {\rm H} + {\rm RO}_{2}^{.} $$\end{document}is shown to quench the possible contributions to termination of adventitiou

ISSN:0538-8066    

DOI:10.1002/kin.550120304

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe bond‐strength–bond‐length (BSBL) method was used to estimate Arrhenius parameters and rate coefficients for various hydrogen atom transfer reactions of the type A + BC → AB + C. In most cases predicted activation energies agreed within 1.2 kcal/mol with the experimental values (average error = 1.12 and standard deviation = 1.42), and the calculated logAagreed within 0.55 log units with the literature data (average error = 0.47 and standard deviation = 0.57). Predicted activated complex properties were shown to agree very well with potential energy surface properties obtained fromab initioquantum mechanical calculations. Detailed comparison of the BSBL results and the results of bond‐energy–bond‐order (BEBO)‐type calculation

ISSN:0538-8066    

DOI:10.1002/kin.550120305

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550120301

出版商:John Wiley&Sons, Inc.    

年代:1980

数据来源: WILEY