摘要:

AbstractThe Diels–Alder addition of acrolein to cyclohexa‐1,3‐diene has been studied between 486 and 571°K at pressures ranging from 55 to 240 torr. The products are endo‐ and exo‐5‐formylbicyclo[2.2.2]oct‐2‐ene (endo‐ and exo‐FBO), and their formations are second order. The rate constants (in l./mole · sec) are given by\documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} {\rm}k_{{\rm endo}} = -(19,470 \pm 50)/4.576T + (5.65 \pm 0.02)$$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} {\rm}k_{{\rm exo}} = - (20,630 \pm 50)/4.576T + (5.51 \pm 0.02)$$\end{document}The retro‐Diels–Alder pyrolysis of endo‐FBO has also been studied. In the ranges of 565–638°K and 6–38 torr, the reaction is first order, and its rate constant (in sec−1) is given by\documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} {\rm}k_{{\rm p}} = - (46,390 \pm 110)/4.576T + (12.98 \pm 0.04)$$\end{document}The reaction mechanism is discussed. The heat of formation and the

ISSN:0538-8066    

DOI:10.1002/kin.550080502

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractAtomic absorption and fluorescence spectrophotometry have been routinely used in kinetic investigations as probes of relative, rather than absolute, atom concentration. The calibration of a Lyman‐α photometer for measurement of absolute hydrogen atom concentrations at levels [H] ι ≤ 1.8 × 1014atoms/cm2and total pressure of 1.5 torr He is described. The photometer is characterized in terms of a two‐level emission source and an absorption region in which only Doppler broadening of the transition is considered. The modifications due to pressure broadening by high pressures (500 ≤P≤ 1500 torr) in the absorption region are discussed in detail. Application of the technique is reported for the recombination of hydrogen atoms in the presence of six nonreactive heat bath gases. Experiments were performed in a static reaction cell at pressures of 500–1500 torr of heat bath gas, and hydrogen atoms were produced by Hg (3P1) photosensitization of H2. The technique is critically evaluated and the mechanistic implications of the hydrogen atom recombination results are examined. The measured room temperature recombination rate constants in H2, He, Ne, Ar, Kr, and N2are 8.5 ± 1.2, 6.9 ± 1.5, 5.9 ± 1.5, 8.0 ± 0.8, 10.2 ± 0.9, and 9.6 ± 1.4, respectively, where the units are

ISSN:0538-8066    

DOI:10.1002/kin.550080503

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe kinetics of chlorine atom abstraction from the chloromethanes (ClM), CCl4, CHCl3, CH2Cl2, and CH3Cl by radiolytically generated trichlorosilyl radicals was studied in the liquid phase by a competitive method. Arrhenius parameters of chlorine atom abstraction from chloromethanes relative to that of bromine atom abstraction from cyclohexyl bromide (RBr) were as follows:The error limits are two standard deviations (2σ) from least mean square Arrhenius plots. From the linear correlation betweenEclvalues derived from the reactions of SiCl3and cyclohexyl radicals with the ClM series it is estimated thatEcl(R + CH3Cl) ≃ 16 kcal/mole. In addition the relative Arrhenius parameters for the hydrogen atom abstraction from SiHCl3and chlorine atom abstraction from CCl4by cyclohexyl radicals were obtained logAH/Acl= 0.12 ± 0.15 andEH−Ecl= 0.24 ± 0.26. TheEH−Eclvalue was combined with existing data onE(R + CCl4) to yield theEH(R+ SiHCl

ISSN:0538-8066    

DOI:10.1002/kin.550080504

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractA competitive technique employing the SO2(3B1) photosensitized isomerization ofcis‐C2F2H2totrans‐C2F2H2in the presence of selected fluorinated olefins has been used at 3712 Å and 22°C to determine the quenching rate constants of the reaction\documentclass{article}\pagestyle{empty}\begin{document}${\rm SO}_{\rm 2} ({}^3B_1){\rm M}\mathop \to \limits^{k_{_4}}$\end{document}removal. WithPSo2= 25.4 torr andPcis‐C2F2H2= 0.239 torr Stern–Volmer plots for M = C2H4, C2H2F, 1,1‐C2F2H2, C2F4, and C3F6yieldedk4(units of 1010l./mole · sec) values of 5.29 ± 0.16, 4.21 ± 0.53, 1.92 ± 0.23, 0.575 ± 0.060, and 0.0335 ± 0.0027, respectively. The results were consistent with the ability of an olefin to quench SO2(3B1) being inversely proportional to the polarizability of the olefin's π bond and the effect can be clearly noted as each H atom in C2H4is individually rep

ISSN:0538-8066    

DOI:10.1002/kin.550080505

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe isomerization of cycloheptatriene at high temperatures (800–1250°K) has been studied experimentally using a shock tube at high pressures and by very low‐pressure pyrolysis in the intermediate‐pressure region (the first direct use of the latter technique for an isomerization). Rate coefficients obtained are in accord with previous results at lower temperatures. The results are examined theoretically to account for weak‐collision nonequilibrium effects. These corrections are found to be appreciable at the temperatures

ISSN:0538-8066    

DOI:10.1002/kin.550080506

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe gamma radiation induced decomposition of MeSO2Cl in cyclohexane (RH) was studied between 60 and 150°C. Throughout this temperature range the reaction proceeds by a free radical chain mechanism. Its propagation is described by the following reactions:The kinetic analysis of the results of the experiments with added SO2, which were carried out in the temperature range of 80 to 150°C, gives 14.94 ± 0.92 and 11.91 ± 0.82 kcal/mole forD(Me‐SO2) andD(c‐C6H11‐SO2), respectively. These bond dissociation energies are considerably lower than the gas‐phase values, and the possible cause of this difference is discussed. Present results also seem to indicate thatD(MeSO2‐H) does not exceed 95 kcal/mole. Competitive experiments with added tetrachloroethylene result in\documentclass{article}\pagestyle{empty}\begin{document}$$\log k_{2{\rm a}} (1./{\rm mole} \cdot {\rm sec}) = 9.07 \pm 0.17- (4.92 \pm 0.21)/\theta $$\end{document}where θ = 2.303

ISSN:0538-8066    

DOI:10.1002/kin.550080507

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractRate constants of change transfer reactionskCT, involving C3C9alkanes and cycloalkanes, have been determined in an ion cyclotron resonance mass spectrometer. The rate constants are significantly lower than the corresponding rate constants for collision when the reaction is less than about 0.5 eV exothermic for linear alkane ions, or less than about 0.2 eV exothermic for cycloalkane ions. In this region of low reaction efficiency, the efficiency of reaction with linear or branched alkanes seems to depend primarily on reaction exothermicity. (The efficiencies of reaction of a given ion with cyclic alkanes also depend on ΔHrn, but are higher than for reactions with other compounds). Although the lowered reaction efficiencies probably result, at least in part, from unfavorable Franck–Condon factors in the energy range near the ionization onset, quantitative correlations between reaction efficiency and estimated relative Franck–Condon factors were not observed. When the enthalpy of reaction is small (less than about −0.15 eV), it is seen that the reverse charge transfer can also occur, and equilibrium is established under the conditions of these experiments. From the observed equilibrium constants, values for the standard free energy change are derived, and assuming that ΔSis small for electron transfer equilibria, values of ΔHrnare estimated. In the case of the equilibria involving cyclohexane ion, these values of ΔHrnlead to estimates of the ionization potentials of methylcyclopentane, 3‐methylpentane,n‐octane, 2,2‐dimethylbutane, and 2,3‐dimethylbutane, which are lower than the ionization potentials of cyclohexane, that is,<9.88 eV, although all these compounds had previously been reported to have ionization potentials above 10.03 eV. That the ionization potentials are indeed lower than 10.03 eV is confirmed by determining the quantum yields of ionization with 10.03‐eV photons.It is pointed out that the conclusions reached here apparently also apply to the charge transfer reactions of alkane ion

ISSN:0538-8066    

DOI:10.1002/kin.550080508

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractThe kinetics of the proton transfer between hydroxyl ions and phenylazoresorcinol, 4‐(p‐nitrophenylazo), and 4‐(m‐nitrophenylazo) resorcinol have been investigated at 25°C and an ionic strength of 0.1M, in a wider pH range than had been done by previous authors. The rate at first decreased with decreasing [OH−], reached a minimum, and then started to increase with decreasing [OH−]. This unusual effect is explained by a mechanism suggested earlier for tropaeolin O. Rate constants and equilibrium constants have been evaluated and discussed.The experimental data were obtained by the T

ISSN:0538-8066    

DOI:10.1002/kin.550080509

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractSeveral fluorine‐containing ethanes (monofluoro, 1,1‐difluoro, 1,1,1‐trifluoro, 1,1,2‐trifluoro, 1,1,2,2‐tetrafluoro, and pentafluoro) and ethenes (1,1‐difluoro and trifluoro) form hydrogen fluoride when irradiated with gamma rays in the gas phase at 25°C. Hydrogen fluoride is apparently formed from fluoroethanes by a mechanism which involves formation of an intermediate semiion pair. We observed identical HF yields both in the absence and presence of molecular oxygen, except for monofluoroethane. A reduction ofG(HF) with increasing sample pressure, for example, of 1,1,2,2‐tetrafluoroethane, indicates that collisional stabilization of excited fluoroethane molecules competes with the process of HF elimination. HighGvalues for HF and CO2in mixtures of CF2CFH and O2reveal the occurrence of

ISSN:0538-8066    

DOI:10.1002/kin.550080510

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY

摘要:

AbstractMeasurements of hydroxyl radical (HO) concentrations in ambient air by the technique of laser‐induced fluorescence have been recently reported. The present study was undertaken to provide an independent test of the validity of those measurements. A photochemical reactor was used to provide a source of HO, and the concentration of HO in the reactor was determined by the laser‐induced fluorescence technique. The HO concentration was also deduced from measured hydrocarbon decay rates in the reactor. There was agreement between the HO concentrations obtained by these two different methods, thus providing further validation of the fluorescence method. Some studies of HO fluorescence efficiency as well as of possible interferences with the fluorescence measurements are repor

ISSN:0538-8066    

DOI:10.1002/kin.550080511

出版商:John Wiley&Sons, Inc.    

年代:1976

数据来源: WILEY