摘要:

AbstractThe thermal reactions ofendo‐ andexo‐5‐cyanobicyclo‐[2.2.2]oct‐2‐ene and theirtrans‐ andcis‐6‐methyl‐substituted derivatives have been investigated in the gas phase between 518 and 630 K. Each product decomposes by two parallel first‐order retro‐Diels‐Alder reactions, a main one with formation of cyclohexa‐1,3‐diene and a minor one with elimination of ethene. Slight isomerizations are also observed. The kinetic results can be explained in terms of a biradical mechanism. The rate‐determining step is shown to depend on the amount of resonance energy in the biradical. Heats of formation and entropies of the bicyclo[2.2.2]o

ISSN:0538-8066    

DOI:10.1002/kin.550191002

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

Abstractn‐Hexyl ands‐octyl radical isomerizations by intramolecular hydrogen atom shift have been studied in the presence of high methyl radical concentration where isomerized alkyl radicals reacted predominantly by combination and disproportionation reactions with methyl radicals.By assuming the rate coefficient of 1‐hexyl radical recombination to be equal to that of ethyl self‐combination, the rate coefficient of log(k1/s−1) = (9.5 ± 0.3) – (11.6 ± 0.3) kcal mol−1/RTln 10 has been derived for the 6spisomerization ofn‐hexyl radicals, 1‐hexyl → 2‐hexyl (1).Investigation ofs‐octyl radical isomerization was complicated by fast interconversion between 3‐octyl, 2‐octyl, and 4‐octyl radicals. Use of the methyl trapping technique and systematic variation of methyl radical concentration made possible the determination of log(k2/s−1) = (9.4 ± 0.7) − (11.2 ± 1.0) kcal mol−1/RTln 10 for the 6ssisomerization of 3‐octyl and the estimation of log(k3/s−1) = 10.5–17 kcal mol−1/RTln 10 for the 5ssisomerization of 2‐octyl radicals, where

ISSN:0538-8066    

DOI:10.1002/kin.550191003

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe standard deviations (σ) of the parameters of a single exponential function can vary strongly with the range of the data, the character of the underlying error structure and also with the inclusion or omission of the appropriate relative weights. These effects are studied quantitatively, for least squares analysis of uniformly spaced,ln‐linearized simulated data. The parameters,kandA, extracted are less precise when weighting is omitted, increasingly so as the range of the data increases, particularly for the case of equal amplitude errors for eachAexp(–kti) datum. The results, expressed as efficiencies (σ2[using weights]/σ2[omitting weights]), show99% of the data and treating the remainder with proper relative wei

ISSN:0538-8066    

DOI:10.1002/kin.550191004

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe rate constant of the primary decomposition step was determined for four symmetrical and four unsymmetricalazoalkanes. From the experimental activation energies and some literature enthalpy data, the following enthalpies of formation of radicals and group contributions were calculated: ΔHƒ(CH3N2) = 51.5 ± 1.8 kcal mol−1, ΔHƒ(C2H5N2) = 44.8 ± 2.5 kcal mol−1, ΔHƒ(2−C3H7N2) = 37.9 ± 2.2 kcal mol−1, [NA‐(C)] = 27.6 ± 3.7 kcal mol−1, [NA‐(ṄA) (C)

ISSN:0538-8066    

DOI:10.1002/kin.550191005

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

摘要:

AbstractBenzylic H‐atom abstraction rates by diphenylmethyl radicals from a series of donors were determined in nonpolar liquids at elevated temperatures. Relative rates were converted to absolute rates via available equilibrium constant data for the dimerization of diphenylmethyl radicals. Abstraction by diphenylmethyl from 1, 2, 3, 4‐tetrahydronaphthalene (tetralin) was studied over the temperature range 489–573 K. Its Arrhenius expression is 109.9±0.3exp{−(10183 ± 373)/T} M−1s−1. Abstraction from other donors was studied at 548 K. Rate constant values ranged from a low of 3.6 M−1s−1for toluene to a high of 3000 M−1s−1for 9, 10‐dihydroanthracene. Similar reactions with the fluorenyl radical were also studied. In this case, relative rates were converted to absolute rates with an equilibrium constant for fluorenyl dimerization determined from the observed homolysis rate of the dimer and an assumed recombination rate. In addition, forward and reverse rate measurements yielded the equilibrium constant for hydrogen transfer between fluorenyl and diphenylmethyl. At 548 K, fluorenyl is favored by a factor of

ISSN:0538-8066    

DOI:10.1002/kin.550191006

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY

ISSN:0538-8066    

DOI:10.1002/kin.550191001

出版商:John Wiley&Sons, Inc.    

年代:1987

数据来源: WILEY