摘要:

AbstractThe kinetics of the gas‐phase decomposition of 1‐methylcyclohex‐1‐ene has been studied over the temperature range of 1000°–1180° K in a single‐pulse shock tube using a comparative‐rate technique. The retro Diels‐Alder reaction to ethylene and isoprene accounts for the bulk of the products with a rate constant given by\documentclass{article}\pagestyle{empty}\begin{document}$$ k = 10^{15.57} \exp \left({- 35,000/T} \right)\sec ^{- 1

ISSN:0538-8066    

DOI:10.1002/kin.550100302

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA previously developed model for active species concentration profiles in infinite cylindrical systems has been extended to include the spherical system. The model couples the processes of diffusion to and reaction at the wall. Predictions of time buildup under conditions of homogeneous production by light, and time decay after extinguishing the light source, are made for H atoms. Such predictions require a knowledge of the wall recombination coefficient and the binary diffusion coefficient for H in heat bath gas. The model is experimentally tested by measuring the first‐order decay constants of H at room temperature in various pressures (10‐1500 torr) of six heat bath gases. The atomic concentration is monitored by Lyman‐α absorption photometry. The results show good agreement with model predictions in the various heat bath gases up to ∼400 torr and depend only on one parameter,γ, the recombi‐nation coefficient. This should be contrasted with the earlier work where slight variation in γ was invoked. The rate constants at pressures higher than 400 torr are consistently higher than model

ISSN:0538-8066    

DOI:10.1002/kin.550100303

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe title reaction, displaying peculiar characteristics as to relative rates and isomer distributions, has been studied in detail. Prior to this study, different mechanisms had been advanced by several groups. Kinetic features (isomer patterns, relative and absolute rates, reaction orders, influences of additives, H/D isotope effects) strongly point to a free‐radical (chain) process, in which (1) is a crucial step. This abstraction reaction, endothermal by about 6 kcal/mol, apparently proceeds via a transition state closely resembling the free aryl radical. Relative rates and isomer distributions therefore reflect differences in stabilization energies, or inDH°(Ar – H). With high arene–Cl2intake ratios or, more pronounced, with CCl4as the reagent, aryl radicals also lead to biaryl, where arene successfully competes with the halogenating agent. This interpretation is quantitatively supported by our observation that “added,˝” recognizable aryl radicals yield the same chlorination–arylation product ratio, and by the results of competitive chlorination of benzene and chloroform over a temperature range of 200°C, where the latter study substantiates the valueDH0(C6H5– H

ISSN:0538-8066    

DOI:10.1002/kin.550100304

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe homogeneous thermal isomerization of cyclopropane to propene was studied in the presence of large excesses (99.6%–99.8%) of argon or helium diluent. Reaction temperatures ranged from 1038°−1208°K, and total gas pressures were varied from 533 to 5097 torr. The comparative‐rate single‐pulse shock‐tube method was used, with the well characterized decomposition of cyclohexene serving as the internal standard reaction. Comparison of the measured rate constants for cyclopropane isomerization withk∞values extrapolated from “preferred˝” lower‐temperature rate constants suggests that collision efficiencies for helium and argon relative to cyclopropane, under the present conditions, are βc≈ 0.04 and 0.05, respectively. Although the uncertainties are rather large, these results do not support the suggestion that rapidly declining βcvalues are largely responsible for the anomalously low rate constants for this reaction atT≥1130°K previousl

ISSN:0538-8066    

DOI:10.1002/kin.550100305

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe decomposition of acetonyl bromide, isopropenylmethylether, and hexanedione‐2,5 was studied using the very‐low‐pressure pyrolysis (VLPP) technique. The acetonyl radical is a product of each reaction. Arrhenius parameters determined are or acetonyl bromide ← acetonyl + Br:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log k\left({\sec ^{- 1}} \right) = 16.0 - 62.5/\theta\,{\rm at}\,300^{\rm o} {\rm K} $$\end{document}and for isopropenylmethylether ← acetonyl + CH3:\documentclass{article}\pagestyle{empty}\begin{document}$$ \log k\left({\sec ^{- 1}} \right) = 15.8 - 66.3/\theta\,{\rm at}\,300^{\rm o} {\rm K} $$\end{document}These lead to values of acetonyl stabilization energy (SE) of 0.8 and −4.0 kcal/mol, respectively. Comparison of the pyrolyses of hexanedione‐2,5 and 2,5‐dimethylhexane indicate a value of SE ∼ 2 kcal/mol. The total of these results is taken, along with previous work, to indicate that 0

ISSN:0538-8066    

DOI:10.1002/kin.550100306

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe pyrolysis of ethylene–butene‐2 mixtures has been studied in a static system over the temperature range of 689°‐754°k and for initial pressures of each olefin of 20–200 torr. The two main addition products were cyclopentene and 3‐methylpentene‐1. Kinetic evidence indicated that cyclopentene was formed from radical processes while 3‐methylpentene‐1 was formed by the molecular “ene¨︂” addition of ethylene to butene‐2 through a six‐center transition state. The following rate constants were obtained:The pyrolysis of 3‐methylpentene‐1 has been studied over the same temperature range and for initial pressures of 20–100 torr. Kinetic evidence showed that the products ethylene and butenes were formed in both radical and molecular processes. Estimates of the rate constantk−1tandk−1cwere, however, in reasonable agreement with the measurements ofk1tandk1c. The mechanism of the ene reaction is discussed, and it is concluded that the transition state does no

ISSN:0538-8066    

DOI:10.1002/kin.550100307

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550100301

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY