ISSN:0538-8066    

DOI:10.1002/kin.550191102

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractA new determination of the disproportionation/combination ratio for C2F5and C2H5radicals gives a value of Δ(C2F5, C2H5) = 0.24 ± 0.02, independent of temperature. The cross‐combination ratio for the two radicals was found to increase with temperature and the significance of this is discussed in evaluatin

ISSN:0538-8066    

DOI:10.1002/kin.550191103

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe thermal decomposition of acetylene has been studied in the temperature and pressure regimes of 1900–2500 K and 0.3–0.55 atm using a shock tube coupled to a time‐of‐flight mass spectrometer. A series of mixtures varying from 1.0–6.2% C2H2diluted in a Ne‐Ar mixture yielded a carbon atom density range of 0.24–2.0 × 1017atoms cm−3in the reflected shock zone. Concentration profiles for C2H2, C4H2, and C6H2were constructed during typical observation times of 750 μs. C8H2and trace amounts of C4H3were found in relatively low concentrations at the high‐temperature end of this study. A mechanism for acetylene pyrolysis is proposed, which successfully models this work and the results obtained by several other groups employing a variety of analytical techniques. Two values of the heat of formation for C2H(134 ± 2 and 127 ± 1 kcal/mol) were employed in the modeling process; superior fits to the data were attained using the latter value. The initial step of acetylene decomposition involves competition between two channels. In mixtures (200 ppm, the dominant initial step is second order. The rate constant for the second‐order reaction is described by the equation\documentclass{article}\pagestyle{empty}\begin{document}$$ k = 2 \times 10^{13} \exp\, {\rm }(- 44.5{\rm\, kcal/}RT){\rm cm}^{\rm 3}\, {\rm mol}^{{\rm - 1}} {\rm s}^{{\rm - 1}} $$\end{document}Benzene concentrations predicted by the model are below the TOF detectability limit. C4H3was observed in the 6.2% C2H2mixture in accordance

ISSN:0538-8066    

DOI:10.1002/kin.550191104

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractFollowing earlier room‐temperature studies, gaseous mixtures of methyl cyclobutyl ketone (MCK) diluted in argon have been photolyzed at temperatures up to 205°C. Experiments have been carried out at a variety of pressures (up to ca. 2 atm) at wavelengths of 313 nm (steady state conditions) and 308 nm (pulsed photolysis). The results are consistent with a mechanism dominated by radical‐radical reactions involving acetyl, methyl, and cyclobutyl radicals. Acetyl radical processes predominate at lower temperatures while methyl radical reactions are more important at high temperatures.The results are interpreted via kinetic modelling of a mechanism in which a key role is played by the acetyl radical decomposition reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ ({\rm M} +)\,{\rm CH}_{\rm 3} {\rm CO}\mathop {\longrightarrow}\limits^{\rm 3} {\rm CH}_{\rm 3} + {\rm CO\, (+ M)} $$\end{document}Values fork3have been obtained and its temperature and pressure dependence are fitted by RRKM theory and a weak‐collisional activation model to yield\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log(}k_3 ^\infty /{\rm s}^{ - 1}) = 13.3 - 17.5{\rm\, kcal\, mol}^{{\rm - 1}} /RT\ln 10 $$\end{document}This high‐pressure limiting Arrhenius equation is consistent with other studies in the same temperature range, but is difficult to reconcile with higher temperature invest

ISSN:0538-8066    

DOI:10.1002/kin.550191105

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractAbsolute rate constants were determined for the gas phase reactions of OH radicals with a series of aliphatic alcohols using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 Torr. The kinetic data for methanol (k1), ethanol (k2), and 2‐propanol (k3) were used to derive the Arrhenius expressions\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = (4.8 \pm 1.2) \times 10^{ - 12} \exp [- (480 \pm 70)/T]\,{\rm cm}^3\, {\rm molecule}^{ - 1} {\rm s}^{ - 1} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 = (7.4 \pm 3.2) \times 10^{ - 12} \exp [- (240 \pm 110)/T]{\rm cm}^3 {\rm molecule}^{ - 1} {\rm s}^{ - 1} $$\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$$ k_3 = (5.8 \pm 1.9) \times 10^{ - 12} \exp [- (30 \pm 90)/T]\,{\rm cm}^3\, {\rm molecule}^{ - 1} {\rm s}^{ - 1} $$\end{document}At 296 K, the measured rate constants (in units of 10−13cm3molecule−1s−1) were:k1= (8.61 ± 0.47),k2= (33.3 ± 2.3), andk3= (58.1 ± 3.4). Room temperature rate constants for the OH reactions with several other aliphatic alcohols were also measured. These were (in the above units): 1‐propanol, (53.4 ± 2.9); 1‐butanol, (83.1 ± 6.3) and 1‐pentanol, (108 ± 11). The results are discussed in terms of the mechanisms for these reactions and are compared to p

ISSN:0538-8066    

DOI:10.1002/kin.550191106

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe mechanism of ligand substitution in 17‐ and 19‐electron organometallic radicals is discussed. These species substitute ligands by an associative process some 106to 1010faster than analogous 18‐electron complexes. When 17‐electron species can be generated by bond homolysis or electron transfer reactions of 18‐electron complexes, they can act as intermediates in radical chain reactions of 18‐electron complexes. A 17–19 electron rule is proposed to explain transformations of organometallic radicals just as the 16–18 electron rule finds use for closed shell organometallic complexes. The origin of this rule is the favorable two‐center three‐electron bond that can form when an odd electron in a sterically accessible metald‐orbital interacts with an electron pair on an entering nucleophile. Besides simple substitution, these radicals can disproportionate, dimerize, and undergo insertion or atom

ISSN:0538-8066    

DOI:10.1002/kin.550191107

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550191101

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY