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  • Physical Chemistry  (90)
  • 1975-1979  (90)
  • 1970-1974
  • 1977  (90)
  • 1
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equilibrium constant for the reaction has been determined between 331 and 480°K using a variable-temperature flowing afterglow. These data give ΔH°(1) = -1.03 ± 0.21 kcal/mol and ΔS°(1) =  - 4.6 ± 1.0 cal/mol°K. When combined with the known thermochemical values for HBr, Br-, and HNO3, this yields ΔHf298°(NO3-) = -74.81 ± 0.54 kcal/mol and S298°(NO3-) = 59.4 cal/mol·°K. In addition ΔHn-1,n and ΔSn-1,nfor the gas-phase reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm NO}_3^- \cdot ({\rm HNO}_3)_{n - 1} + {\rm HNO}_3 \to {\rm NO}_3^- \cdot ({\rm HNO}_3)_n $$\end{document} were determined for n = 2 and 3. The implications of these measurements to gas-phase negative ion chemistry are discussed.
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  • 2
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of chlorine atom abstraction from the chloroethanes (EClH) 1,1,2-C2Cl3H3, 1,1-C2Cl2H4, and 1,2-C2Cl2H4 by radiolytically generated cyclohexyl radicals was studied in the liquid phase by a competitive method. The chlorine atom abstraction data were put on an absolute basis by comparing the rates of the metathetical reactions with the known rate of addition of cyclohexyl radicals to C2Cl4. The following Arrhenius parameters were obtained: TextE(EClH)-TemperatureA(ECLH)E(CCl4)log A(EClH)E(EClH)RangelogEClHA(C2Cl4)(kcal/mol)(1.mol·sec)(kcal/mol)(°C)CHCL2CH2Cl0.03 ± 0.083.87 ± 0.178.98 ± 0.1411.17 ± 0.27150 - 250CHCL2CH30.13 ± 0.134.63 ± 0.278.18 ± 0.1911.93 ± 0.37130 - 250CHCL2CH2Cl0.50 ± 0.177.57 ± 0.359.18 ± 0.2314.87 ± 0.45150 - 250The error limits are the standard deviations from least mean square Arrhenius plots.The α and ß activation effects on the kinetics of Cl atom abstraction from chloroalkanes are discussed. From the linear relation between the relative reactivities of cyclohexyl radicals toward the XCCl3 and XCHCl2 series, ECl(c-C6H11· + CHCl2CHCl2) = 10.2 ± 1 kcal/mol and ECl(c-C6H11· + CHCl22CCl3) = 9.7 ± 1 kcal is derived.
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  • 3
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    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of OH(v = 1) with HBr, O, and CO have been studied at 295°K using a fast discharge flow apparatus: The reaction O + HBr → OH(v = 1) + Br was used as a source of OH(v = 1), and subsequent chemical reactions of the excited radical were followed using EPR spectroscopy. Rate constants for reactions (2b), (3b), and (6b) were measured as (4.5 ± 1.3) × 10-11, (10.5 ± 5.3) × 10-11, and 〈5 × 10-12 cm3/molec·sec, respectively. The rate constant for physical deactivation of OH(v = 1) by CO was determined as 〈4 × 10-13 cm3/molec·sec.
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  • 4
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No. Abstract.
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  • 5
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Computer calculations of the kinetics of the ferric ion catalyzed decomposition of H2O2 by Walling and Weil are not in contradiction to the “complex mechanism.” The examination of their results reveals that their simulations correspond to the terminal state of the system in which the secondary complex between Fe3+ and H2O2 becomes stabilized.
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  • 6
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    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The unimolecular decomposition of chemically activated methylallylether (MAE) formed by the cross combination of methoxymethyl and vinyl radicals was studied in the gas phase. The experimentally determined rate constant was found to be 1.11 × 108 sec-1 at 9.6°C for the decomposition of MAE into propene and formaldehyde. The decomposition of MAE via the six-center retro-“ene” type transition state is analyzed by using the RRKM unimolecular reaction theory. For the molecular parameter assignments of energized MAE, a model which contains one internal rotational mode is supported, and MAE decomposition is characterized by a tight complex model. The best agreement between experimental and theoretical results was found when a critical energy of 40.1 kcal/mol was used.
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  • 7
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The low-pressure recombination rate constants of the reactions I + NO + M → INO + M (with 14 different M) and I + NO2 + M → INO2 + M (with 26 different M) have been measured at 330°K by laser flash photolysis. The collision efficiencies βc are analyzed and compared with other thermal activation systems. Whereas βc increases in one reaction with an increasing number of atoms in M, practically no such effect is found when, for the same M, different reactions with varying complexities of the reacting molecules are considered.
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  • 8
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal reaction of 1,3-butadiene (BD) has been studied between 464 and 557°K at pressures between 49 and 450 torr. The products are 4-vinylcyclohexene (VCH) and cis, cis-cycloocta-1,5-diene (COD), and their formations are second order. The rate constant (in 1/mol · sec) for VCH is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{10} k_{\rm V} = - (24,530 \pm 120)/4.576T + (6.95 \pm 0.05) $$\end{document} and that for COD by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{10} k_{\rm C} = - (28,440 \pm 100)/4.576T + (7.65 \pm 0.04) $$\end{document}The thermal reaction of COD has also been studied. The temperature was varied from 505 to 586°K and the pressure from 15 to 51 torr. The rate constants (in sec-1) for the formations of VCH and BD are given by \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm log}_{10} k_{{\rm VCH}} = - (51,780 \pm 120)/4.576T + (15.34 \pm 0.05) \\ {\rm log}_{10} k_{{\rm BD}} = - (56,380 \pm 100)/4.576T + (16.46 \pm 0.04) \\ \end{array} $$\end{document}A biradical mechanism seems to fit these results. The heat of formation and the entropy of COD are estimated.
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  • 9
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal unimolecular decomposition of 2-phenylethylamine (PhCH2CH2NH2) into benzyl and aminomethyl radicals has been studied under very-low-pressure conditions, and the enthalpy of formation of the aminomethyl radicals, ΔH°f, 298K (H2NCH2·) = 37.0 ± 2.0 kcal/mol, has been derived from the kinetic data. This result leads to a value for the C - H bond dissociation energy in methylamine, BDE(H2NCH2 - H) = 94.6 ± 2.0 kcal/mol, which is about 3.4 kcal/mol lower than in C2H6 (98 kcal/mol), indicating a sizable stabilization in α-aminoalkyl radicals.
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  • 10
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    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal and methyl radical initiated decomposition of biacetyl-d6 were investigated at conversions 5% over the temperature range of 387-412°C and 251-292°C, respectively. The deuterated sample contained 10.5% biacetyl-d5. The reaction products were analyzed by mass spectrometry.The following data could be determined from product ratios: where E is in kcal/molWith reasonable assumptions and literature data Arrhenius parameters for elementary steps were derived and discussed in particular with respect to isotopic effects in H/D-abstraction reactions.
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  • 11
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calculations of the nonequilibrium rate constant for the model system H2O2 + M → 2 OH + M over the temperature range of 300-1900°K, assuming that only vibrational, or that both vibrational and rotational, energy is transferred in a collision, show that (1) inefficient energy transfer leads to a distinctly non-Arrhenius temperature dependence, the nonlinearity being in principle different for different M, and (2) despite different activation energies for different M, the order of M efficiencies is preserved throughout the temperature range. A reversal of M efficiencies can occur only if there is a change of mechanism of the reaction over the temperature range investigated.
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  • 12
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the thermal decomposition of 2,3-dimethyl-3-pentyl acetate have been studied at a temperature range of 212-260°C and a pressure range of 30-300 mm Hg. The olefins produced are 2-ethyl-3-methyl-1-butene, 3,4-dimethyl-trans-2-pentene, 3,4-dimethyl-cis-2-pentene, and 2,3-dimethyl-2-pentene. The reaction is homogeneous, obeys first-order law, and the value of the rate constant is given by the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}\,k({\rm sec}^{- 1}) = (14.22 \pm 0.23) - (40,600 \pm 500)\,{\rm cal}/{\rm mol}/2.303RT $$\end{document} The directions of elimination and their corresponding partial rates are best explained in terms of purely steric factors.
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  • 13
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants for hydrogen transfer reactions from C - H bonds to O(3P) in the gas phase have been calculated by the bond-energy bond-order method. The use of a single or double triplet repulsion term is discussed. Computational results indicate that with carefully selected input parameters, it is unnecessary to use a double-repulsion term. Tunneling corrections were carried out by two different procedures. Results indicate that in this case there is not much difference between the simple Wigner's treatment and more complicated methods.
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  • 14
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    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of pyrolysis of dimethyl ether wexre studied in an adiabatic flow reactor at temperatures between 790 and 950°C. The unimolecular rate constant for the initiating step CH3OCH3 = CH3O + CH3 was found to be k1 = 2.16 × 1015e-76,600/RTsec-1. Aspects of the kinetic mechanism are discussed and a system postulated to account for the high-temperature products.
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  • 15
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 16
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions between SO2 and O2 were carried out in the presence of TiO2 and NiO under various partial pressures of SO2 and O2 at temperatures from 240 to 330°C. TiO2 and NiO were pretreated by applying an annealing effect from which the catalysts would have the different activity. The rates are the highest for TiO2 pretreated at high temperature in the region of 400 to 600deg;C in vacuum, 1.21 × 10-4 mmHg. In contrast, the rates are the lowest for NiO pretreated at high temperaturefrom 350 to 550°C. The data have been correlated with 1.4 and first-order kinetics for TiO2 and NiO, respectively. A reaction mechanism to explain the data was suggested.The quantities of anionic vacancies in TiO2 surfaces and of positive holes in NiO appeared to be paramount in determining the type of kinetics.
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  • 17
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    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 18
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the gas-phase thermal decomposition of 1,1,2-trifluoro-2-trifluoromethyl-cyclopropane to 2,3,3,3-tetrafluoropropene and CF2 was studied in the temperature range of 539-604°K and with a total pressure of 17 to 300 torr of a 1:20 mixture of reactant and perfluoroethylene. Some runs were also made with the reactant only, with initial pressures of 0.2 to 20 torr. The reaction is first order, homogeneous, and the rate constants fit the following Arrhenius relationship: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}\,k/{\rm sec}^{- 1}) = (15.23 \pm 0.12) - (50,557 \pm 1100)/4.576T $$\end{document} .
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  • 19
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate of the thermal cycloaddition of ethylene to cis-and trans-butene-2 has been measured at 663, 678, 693, and 703°K, and the energy relations between the reactants, intermediates, and products have been determined. The intermediate biradicals formed from the cis reactants and from the trans reactants were shown to be separated by a small but measurable enthalpy difference. This result further supports the conclusion of Part I that the intermediates are distinct species which retain some of the original configuration of the reactant. The significance of the results in relation to the mechanism of “forbidden” reactions is discussed.
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  • 20
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method proposed in 1972 by W. Forst is used to calculate the experimentally accessible pressure dependence of thermal unimolecular rate constants. The specification of an activated complex always employed in RRKM calculations is avoided. This allows for a more consistent comparison between the results obtained by the application to various unimolecular processes. In order to bring experimental and calculated curves into agreement, fourcenter eliminations of hydrogen halides from alkyl halides require the formal introduction of a collision efficiency factor λ ≃ 0.2, and for the concerted ring opening of 1,1-dichlorocyclopropane λ ≃ 0.4 must be assumed. The isotope effects for the decomposition of CD3CD2Cl and CH3CD2Cl have been studied, and the pressure dependence of kH/kD is reported. Studying the biradical ring opening of oxetan, cyclobutane, and cyclopropane, the falloff curves and isotope effects are predicted within the experimental uncertainty by the use of λ ≃ 1.0. This different behavior of concerted and biradical reactions against falloff calculations can hardly be attributed to experimental uncertainties in the Arrhenius parameters and/or the collision frequency alone.
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  • 21
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nanosecond flash photolysis of 1,2- and 1,8-dinitronaphthalenes (1,2-DNO2N; 1,8-DNO2N) in nonpolar and polar solvents shows transient species with absorption maxima and lifetimes dependent on solvent polarity. In deaerated n-hexane the absorption maxima and lifetimes (1/K) are 490 nm and 1.0 μsec for 1,2-DNO2N and 550 nm and 2.5 μsec for 1,8-DNO2N. In deaerated ethanol the corresponding values are 550 nm and 4.3 μsec for 1,2-DNO2N and 590 nm and 5.3 μsec for 1,8-DNO2N. The transient absorptions are attributed to the lowest triplet excited states T1 of the 1,2- and 1,8-DNO2N. The observed red shifts in the absorption maxima of the T1 states are indicative of the extent to which electronic charge is transferred intramolecularly during the T1 → Tn transitions. Furthermore, the increased lifetime of the T1 states with increasing solvent polarity indicates the intramolecular charge transfer character of the T1 states. Changes of dipole moments accompanying the T1 → Tn transitions as well as rate constants for electron or proton transfer and hydrogen abstraction reactions involving the T1 states of 1,2- and 1,8-DNO2N and tributyl tin hydride (Bu3SnH) as the hydrogen donor were determined together with the activation energy of the hydrogen abstraction reaction for the case of 1,2-DNO2N. The spectroscopic and kinetic data obtained in this work demonstrate that the triplet states of 1,2- and 1,8-DNO2N behave like n → π* states in nonpolar media while in polar solvents the n → π* character of these states is reduced with a simultaneous increase in their intramolecular charge transfer character.
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  • 22
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A symbolic mechanism “μH, YH” has been proposed to account for the homogeneous chain pyrolysis of an organic compound μH in the presence of a hydrogenated additive YH at small extents of reaction. An analysis of this mechanism leads to two limiting cases: the thermal decomposition of neopentane corresponds to the first one (A), that of ethane to the second one (B). Previous experimental work has shown that this mechanism seems to account for a number of experimental observations, especially the inhibition of alkane pyrolyses by alkenes.Experimental investigations were extended by examining the influences oftwo hydrogen halides (ClH and BrH) upon the pyrolyses of neopentane (at 480°C) and ethane (around 540°C). The experiments have been performed in a conventional static Pyrex apparatus and reaction products have been analyzed by gas-liquid chromatography.The study shows that ClH and BrH accelerate the pyrolysis of neopentane (into i-C4H8 + CH4). The experimental results are interpreted by reaction schemes which appear as examples of the mechanism “μH, YH” in the first limiting case (A). The proposed schemes enable one to understand why the accelerating influence of ClH is lower or higher than that of BrH, depending on the concentration of the additive. An evaluation of the rate constant of the elementary steps neo-C5H11 · → i-C4H8 + CH3 · is discussed.In the case of ethane pyrolysis, BrH inhibits the formation of the majorproducts (C2H4 + H2) and, even more, that of n-butane traces. The experimental results are interpreted by a reaction scheme which appears as an example of the mechanism “μH, YH” in the second limiting case (B). On the contrary, ClH has no noticeable influence on the reaction kinetics. This result inessentially due to the fact that the bond dissociation energy of Cl—H(⋍103 kcal/mol) is higher than that of C2H5 - H (⋍98 kcal/mol), whereas that of Br - H (⋍88 kcal/mol) is lower.
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  • 23
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Arrhenius parameters are frequently evaluated incorrectly by applying the least squares method to the logarithmic form of the Arrhenius equation without simultaneously transforming the statistical weights as required for the change of variable from k to ln k. This has been mentioned briefly in an earlier paper. In the present communication the correct procedures are discussed and illustrated by several examples of evaluations. In particular, Arrhenius parameters calculated by the Taylor series expansion of the exponential form of the Arrhenius equation are compared with those calculated from the logarithmic form, using an exact and two approximate transformations of the statistical weights. The comparisons indicate thatthe preferred procedure for obtaining Arrhenius parameters is either the Taylor series method or the logarithmic method with proper transformation of the experimentally determined statistical weights of the rate constants ki. The common approximation of assuming equal statistical weights of ln ki when the logarithmic form of the Arrhenius expression is used is shown not to be always appropriate, and reasons forthis are given.
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  • 24
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 25
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of trifluoroacetaldehyde at temperatures f 471 to 519°C has been studied by measuring the rates of formation of CF3H and C2F6. It is concluded that the high-pressure reaction mechanism involves a Rice-Herzfeld reaction scheme with first-order initiation and second-order termination via CF3 combination. However, a falloff in reaction rates is observed at pressures below 100 mmHg. The Arrhenius parameters of the three rate constants corresponding to the overall reaction, the initiation reaction, and an abstraction reaction have been evaluated.
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  • 26
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of propene in the presence of D2 was studied in a single-pulse shock tube in the temperature range of 1200-1400°K. The main decomposition products were methane, ethylene, allene, and propyne. Furthermore, deuterated species were observed of each product and of propene, with characteristic compositions that were dependent on propene conversion. Geometrical isomers of monodeuterated propene, as the result of H-D exchange, were analyzed by microwave spectroscopy. From these observations, the reactivities of n- and isopropyl radicals at high temperatures were determined. The former was found to be an intermediate of methane and ethylene and the latter was found to be responsible for the formation of the deuterated propene as follows: The rate constant ratio kn/ki was estimated to be 0.5-0.8, which was more than ten times greater than that obtained at room temperature. It was also found that allene or propyne was produced from allyl radicals and that acetylene was produced from vinyl radicals. In addition, the rate constant of the hydrogen abstraction by the hydrogen atom from C3H6 was found to be six times greater than that by the hydrogen atom from D2.
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  • 27
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,2-Fluorochloroethane was photolyzed at 147 nm in the pressure range of 3.8-20.9 torr. The effects of added NO, H2S, and large pressures of CF4 were also investigated. The exponential extinction coefficient at 147 nm and 296°K was found to be 147 ± 4 atm-1 · cm-1.The photochemistry in some respects is similar to that of ethyl chloride. The primary processes again appear to involve at least two excited states. One of these yields ethylene by FCl elimination (Φ ≃ 0.3) and has a lifetime of ∼3.2 × 10-10 sec, with respect to an internal conversion to the vibrationally excited ground state or, more probably, a collisionally induced crossover to a state decomposing mainly by carbon—halogen bond fission. The molecular elimination of HCl, H2, and small amounts of HF also occurs but not apparently from the same state as does FCl. The quantum yields of products with radical precursors, however, are not large, and hence little, if any, of the FCl and probably none of HCl, H2, and HF subsequently dissociates. The vinyl fluoride and vinyl chloride, accompanying the elimination of HF and HCl, are postulated as possible sources of the secondary production of acetylene.
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  • 28
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The asymptotic quantum yield of triplet energy transfer is found by calculating the fraction of acceptor molecules with energy above the minimum energy for decomposition. This is done by allowing for a statistical energy distribution among the internal modes in the collision complex. It is found that for a monatomic triplet donor most of the triplet energy is transferred to the acceptor molecule, while for a polyatomic donor molecule only a fraction of it is available for future decomposition of the acceptor.
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  • 29
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate of demetallation of α, β, γ,δ-tetra(p-sulfophenyl)porphineiron (III), Fe(TPPS)3-, was determined in sulfuric acid-ethanol-water media for 8.5-10.65M sulfuric acid at different temperatures. The overall reaction was the conversion of the complex Fe(TPPS)3- into the diacid species H4TPPS2- without other spectrophotometrically important species being formed to an appreciable extent, as shown by three isosbestic points at 418, 462, and 563 nm. The rate was first order in the Fe(TPPS)3- concentration. The pseudo-first-order rate constants k were exponentially dependent on the sulfuric acid concentration, and log k was linearly dependent on the Hammett acidity function -H0. The average ΔH
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  • 30
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction between ozone and thiophene was studied from 30 to 125°C over a pressure range of 0.005-0.3 torr ozone and 0.1-1 torr thiophene. The most abundant product was O2 with smaller amounts of CO2 and SO2. The mass balance was 100% for oxygen and approached 100% for sulfur at the higher values of [O3]0. The carbon balance, however, was only 25% and no H-containing products were found, suggesting that the missing product is a hydrocarbon which may be a polymer. The rate law found was -d[O3]/dt = k1[Th] [O3] + k2 [Th] [O3]2 where log k1(M-1 · sec-1) = 7.8 ± 0.5 - (8400 ± 700)/2.3RT, and log k2(M-2 · sec-1) = 12.4 ± 0.4 - (4700 ± 400)/2.3RT. Added O2 had no effect on k1 but reduced k2 to a limiting value. It is thus not possible to measure the primary rate constant in this system by measuring the overall rate in the presence of oxygen, and this restriction may also apply to other ozone systems. A mechanism is postulated involving two chain sequences, one of which is inhibited by added O2. A comparison with other ozone systems is made, and the chain lengths are far greater for ozone + thiophene than other systems, under the conditions employed. Possible intermediates in the mechanism are discussed.
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  • 31
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of cerous ions by bromate ions in sulfuric acid medium was followed spectrophotometrically under various experimental conditions. The results were compared to the calculated predictions on the basis of a mechanism suggested by R. M. Noyes and collaborators. The computations were done by solving the complete set of the kinetic differential equations. The results of the computations show that the proposed mechanism explains adequately most of our and previous experimental data. In particular, the mechanism predicts the main features of the reaction, namely, the induction and the fast and slow reaction periods which occur during the oxidation.
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  • 32
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    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of NO2 and its atom-transfer reactions with SO2 and CO have been studied behind incident shock waves using photometric detection methods. From the decomposition study it is possible to obtain information on the rate of the reaction 2NO2 → antisymmetric-NO3 + NO. The results on the reaction, NO2 + SO2 → NO + SO3 extend the earlier work of Armitage and Cullis to about 2000°K. The reaction with CO [NO2 +] [CO NO + CO2] at shock temperatures is somewhat faster than predicted from available low-temperature data and provides a modification of the rate-constant expression that is applicable over a wide temperature range.
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  • 33
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nanosecond laser photolytic studies of 4-nitro-N,N-dimethylnaphthylamine (4-NDMNA) in nonpolar and polar solvents at room temperature show a transient species with an absorption maximum in the 500-510-nm range. This species is assigned to the lowest triplet excited state of 4-NDMNA. The absorption maximum of this state is independent of solvent polarity, and its lifetime is a function of the hydrogen donor efficiency of the solvent. In n-hexane the lifetime 1/k of the triplet state is 9.1 × 10-6 sec, while in acetonitrile 1/k is 2.0 × 10-7 sec. The hydrogen abstraction rate constant kH of the triplet state with tributyl tin hydride (Bu3SnH) in n-hexane is 1.7 × 107M-1·sec-1, while in the case of isopropyl alcohol as hydrogen donor, kH is 4.0 × 107M-1·sec-1. The activation energy for the hydrogen abstraction by the triplet state from Bu3SnH in deaerated n-hexane is 0.6 kcal/mol. The lack of spectral shift with increasing solvent polarity, and the appreciable hydrogen abstraction reactivity of the triplet state, also independent of solvent polarity, seem to indicate that this excited state is an n-π* state which retains its n-π* character even in polar media.
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  • 34
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electron pulse radiolysis at ⋍298°K of 2 atm H2 containing 5 torr O2 produces HO2 free radical whose disappearance by reaction (1), HO2 + HO2 →H2O2 + O2, is monitored by kinetic spectrophotometry at 230.5 nm. Using a literature value for the HO2 absorption cross section, the values k1 = 2.5×10-12 cm3/molec·sec, which is in reasonable agreement with two earlier studies, and G(H) G(HO2) ⋍13 are obtained. In the presence of small amounts of added H2O or NH3, the observed second-order decay rate of the HO2 signal is found to increase by up to a factor of ⋍2.5. A proposed kinetic model quantitatively explains these data in terms of the formation of previously unpostulated 1:1 complexes, HO2 + H2O ⇋ HO2·H2O (4a) and HO2 + NH3⇋ HO2·NH3 (4b), which are more reactive than uncomplexed HO2 toward a second uncomplexed HO2 radical. The following equilibrium constants, which agree with independent theoretical calculations on these complexes, are derived from the data: 2×10-20≲K4a≲6.3 × 10-19 cm3/molec at 295°K and K4b = 3.4 × 10-18 cm3/molec at 298°K. Several deuterium isotope effects are also reported, including kH/kD = 2.8 for reaction (1). The atmospheric significance of these results is pointed out.
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  • 35
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general comprehensive model of the two-step photodissociation method of isotope enrichment for diatomic reactants was constructed. The model includes kinetic and absorption processes, isotopic species, and temperature. Criteria to measure different aspects of enrichment were established.The results show that, in general, isotopic mixing by kinetic processes can be controlled. The relative importance of intensities of excitation sources for the two steps depends on the degree of saturation of the first-step absorption transition.For the specific system modeled, i.e., the dissociation of HBr followed by scavenging with NO, the model predicts that detection of bromine enrichment is possible. The important processes and their influence on enrichment were identified, and optimization of experimental parameters was modeled.
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  • 36
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions between alizarin yellow G and six different bases B (including OH-) and between tropaeolin 0 and eight different bases have been investigated at 25°C and an ionic strength of 0.5M, using the temperature-jump method. From the form of the log kB versus ΔpK curves it is concluded that for alizarin yellow G the observed relaxation time is due chiefly to a diffusion-controlled reaction between the base and that fraction which is present in the “open” non-hydrogen-bonded form, whereas for tropaeolin 0 the base attacks the hydrogen bridge.The dissociation constants for the internally bound hydrogen have been measured under the same conditions of temperature and ionic strength, using a spectrophotometric method.
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  • 37
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 1,3-cyclopentadiene (CPD) with ground-state atomic oxygen O(3P), produced by mercury photosensitized decomposition of nitrous oxide, was studied. The identified products were carbon monoxide and the following C4H6 isomers: 3-methylcyclopropene, 1,3-butadiene, 1,2-butadiene, and 1-butyne. The yield of carbon monoxide over oxygen atoms produced (φCO) was equal to the sum of the yields of C4H6 isomers in any experiment. φCO was 0.43 at the total pressure of 6.5 torr and 0.20 at 500 torr. We did not succeed in detecting any addition products such as C5H6O isomers.It was found that 3-methylcyclopropene was produced with excess energy and was partly isomerized to other C4H6 isomers, especially to 1-butyne. The excess energy was estimated to be about 50 kcal/mol.The rate coefficient of the reaction was obtained relative to those for the reactions of atomic oxygen with trans-2-butene and 1-butene. The ratios kCPD+O/ktrans-2-butene+O= 2.34 and kCPD+O/k1-butene+O = 11.3 were obtained.Probable reaction mechanisms and intermediates are suggested.
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  • 38
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A fast discharge flow apparatus equipped for EPR detection of radicals has been used to investigate the reaction O + HBr → OH + Br. At 295°K, measurements showed that more than 97% of all OH produced in this reaction was formed initially in its first vibrationally excited state. Rate constants for physical deactivation of OH(v = 1) by O(3P), Br(2P3/2), H2O, and HBr were measured as (1.45 ± 0.25) × 10-10, (6.4 ± 2.4) × 10-11, (1.35 ± 0.50) × 10-11, and 〈 10-12 cm3/molec·sec, respectively.
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  • 39
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the reaction of O(3P) atoms with acetone were investigated using fast flow methods. The reaction was studied over a temperature range of 298 to 478°K. The specific rate constant obtained was (1.9 ± 0.4) × 1012 exp( - 5040 ± 180/1.987 T) cm3/mol·sec. The observation of a sizable primary H/D kinetic isotope effect in comparing rates of CH3COCH3 and CD3COCD3 led to the conclusion that the major reaction channel involves H atom abstraction, namely, \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm O}(^3 P) + {\rm CH}_3 {\rm COCH}_3 \to {\rm OH} + {\rm CH}_3 {\rm COCH}_3 $$\end{document}The rather low Arrhenius preexponential factor obtained in this reaction is compared and contrasted with those reported for other reactions of O(3P) with low molecular weight compounds.
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  • 40
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A value of the enthalpy of formation of the phenoxy radical in the gas phase, ΔH°,298K (φO·, g) = 11.4 ± 2.0 kcal/mol, has been obtained from the kinetic study of the unimolecular decompositions of phenyl ethyl ether, phenyl allyl ether, and benzyl methyl etherTrivial names for ethoxy benzene, 2-propenoxy (allyloxy) benzene, and α-methoxytoluene, respectively at very low pressures. Bond fission, producing phenoxy or benzyl radicals, respectively, is the only mode of decomposition in each case. The present value leads to a bond dissociation energy BDE(φO - H) = 86.5 ± 2 kcal/mol,1 kcal = 4.18674 kJ (absolute) in good agreement with recent estimates made on the basis of competitive oxidation steps in the liquid phase. A comparison with bond dissociation energies of aliphatic alcohols, BDE(RO - H) = 104 kcal/mol, reveals that the stabilization energy of the phenoxy radical (17.5 kcal/mol) is considerably greater than the one observed for the isoelectronic benzyl radical (13.2 kcal/mol). Decomposition of phenoxy radicals into cyclopentadienyl radicals and CO has been observed at temperatures above 1000°K, and a mechanism for this reaction is proposed.
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  • 41
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions have been studied by a mass-balance method involving the photolysis of small amounts of biacetyl in the presence of a large excess of isobutane containing a small proportion of the unsaturated substrate. The following Arrhenius parameters have been derived: TextTemperatureElog ArangeReaction(kcal/mol)(1./mol·sec)(°K)ĊH3 + C2H4 → Ċ3H77.3 ± 1.08.32 ± 0.5350 - 500ĊH3 + C2H2 → Ċ3H57.7 ± 1.58.79 ± 0.8379 - 487ĊH3 + C6H6 → C7H97.6 ± 1.08.79 ± 0.5372 - 484The results for methyl addition to ethylene are based on previous determinations by other techniques as well as the present studies. The results for methyl addition to acetylene and benzene are derived solely from the present experiments and are calculated relative to a rate constant of log k2(l./mol·sec) = 7.42 - (7.1/θ) for the reference reaction (2), ·H3 + (CH3)3CH → CH4 + ·4H9.
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  • 42
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of oxidation of several substituted quinols by a series of Tris(1,10-phenanthroline)iron(III) complexes has been investigated with a stopped-flow technique at 6.0 and 20.0°C. The reactions were found to be first order on both reactants and independent of acidity. The second-order specific rate constants were strongly dependent on free energy of reaction. An interpretation of the mechanism in the light of Marcus theory has been developed. The first electron abstraction with semiquinone radical formation has been suggested as the rate-determining step, and on this basis, intrinsic parameters of the reactions have been derived. A good agreement was found between experimental and computed data.
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  • 43
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction H + CH3OOH was investigated under conditions of excess atomic hydrogen concentration using a flow reactor attached to a photoionization mass spectrometer. The rate coefficient of the reaction was determined as \documentclass{article}\pagestyle{empty}\begin{document}$$ k = (2.8 \pm 0.9) \times 10^{- 13} {\rm exp\,}[- (1860 \pm 190){\rm cal}/RT \cdot {\rm mol\,}]\,{\rm cm}^3 /{\rm molec} \cdot {\rm sec} $$\end{document} The three important reaction channels were found to be with the individual contributions determined as indicated. The product methoxy and methylperoxy radicals react mainly with atomic hydrogen under the employed experimental conditions according to where the estimates for the percentage contributions of the various channels were derived from the measured product yields.
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  • 44
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate of the thermal cycloaddition of ethylene to cis and trans butene-2 has been measured at 693°K and at pressures of about 12 atmospheres. The ratio of trans- to cis-1,2-dimethylcyclobutane from the reaction of trans-butene-2 with ethylene was 5.1, obtained from the initial rates of formation of the products. Similarly, the ratio of cis- to trans-1,2-dimethyl-cyclobutane from the reaction of cis-butene-2 with ethylene was 2.8. The results show that the cycloaddition reactions are the reverse of the decomposition reactions of the dimethyl-cyclobutanes and may be interpreted in terms of a biradical intermediate. Several ratios of rate constants have been measured as well as the rate constants for the reaction of the olefins to form the intermediate biradical.
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  • 45
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the gamma radiation induced free radical chain decomposition of BrCH2CN in liquid cyclohexane (RH) was investigated over the temperature range of 60-170°C. In addition competitive experiments in the presence of CCl4 were carried out between 80 and 180°C. For the reactions the following Arrhenius expressions were derived: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm log}k_3 /(2k_4)^{1/2} ({\rm l}^{{\rm 1/2}} /({\rm mol} \cdot {\rm sec})^{1/2}) = 4.07 \pm 0.35 - (11.96 \pm 0.63)/\theta \\ {\rm log}k_2 /k_5 = - 0.699 \pm 0.167) + (2.69 \pm 0.31)/\theta \\ \end{array} $$\end{document} where θ = 2.303RT in kcal/mol.The effect of CN substitution on the activation energies of reactions (2) and (3) was evaluated based on the present and previously published results. The CN group effect on halogen atom abstraction [reaction (2)] is discussed in terms of inductive and enthalpic factors.The differences E3 - E(CH3 + RH) and E(CCl2CN + RH) - E(CCl3 + RH), which yield a value of about 5.5 kcal/mol, are considered to reflect the cyano stabilization effect at the radical center confirming D(CH2(CN)-H) ∼ 93 kcal/mol.
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  • 46
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The application of modern theories of energy transfer to unimolecular reactions taking place at very high temperatures is discussed. It is shown that the efficiency of energy transfer for both reactant-reactant and reactant-inert diluent collisions may be substantially smaller than the values determined experimentally at lower temperatures. Consequently at high temperatures unimolecular falloff effects, particularly in some shock-tube measurements, may be greater than has been believed hitherto.The application of these calculations to the unimolecular reactions of cyclopropane, cyclobutane, and cyclohexene at temperatures around 1300°K is discussed, and it is shown that under shock-tube conditions the apparent first-order rate coefficient may be at least ten times less than the high-pressure limiting value.
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  • 47
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nanosecond spectroscopic and kinetic studies of 4-nitronaphthylamine (4-NO2NA) in aerated and deaerated nonpolar solvents at room temperature show a transient species with absorption maxima at 470 and 665 nm. The rate constant for the decay of this species in deaerated benzene is 6.7 × 105 sec-1, while in aerated benzene solutions the species is quenched by oxygen with arate constant k = 2.0 × 109M-1·sec-1. The transient absorption at 470and 665 nm is assigned to the lowest triplet excited state of 4-NO2NA. In polar solvents, however, electronic excitation of 4-NO2NA does not lead to any detectable transient absorption between 400 and 800 nm for the temperature range of 25 to -150°C. This is attributed to lack of intersystem crossing of 4-NO2NA in polar solvents.
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  • 48
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using the technique of molecular modulation spectrometry, we have measured directly the rate constants of several reactions involved in the oxidation of methyl radicals at room temperature: k1 is in the fall-off pressure regime at our experimental pressures (20-760 torr) where the order lies between second and third and we obtain an estimate for the second-orderlimit of (1.2 ± 0.6) × 10-12 cm3/molec · sec, together with third-order rate constants of (3.1 ± 0.8) × 10-31 cm6/molec2 · sec with N2 as third body and (1.5 ± 0.8) × 10-30 with neopentane; we cannot differentiate between k2a and k2c and we conclude k2a + (k2c) = (3.05 ± 0.8) × 10-13 cm3/molec · sec and k2b = (1.6 ± 0.4) × 10-13 cm3/molec · sec; k3 = (6.0 ± 1.0) × 10-11 cm3/molec · sec.
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  • 49
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 50
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermodynamic characteristics of the dissociation of carbon diselenide are examined. Results of a shock-tube study of CSe2 pyrolysis are combined with previously unreported photoionization spectroscopy data on CSe2 and with a critical examination of the available literature on Se(g), Se2(g), CSe(g), CSe2(g), and CSe2(t). Based on the best currently available information, recommendations are made for the values of enthalpies, entropies, heat capacities, and derived functions. In particular, the most likely value for ΔH0 (CSe2(g) → CSe(g) + Se(g, 3P)) is +83 kcal/mol, and for Kp at 2000°K it is 0.018 atm.
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  • 51
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,1,1-Difluorochloroethane (Freon 142) was photolyzed at 147 nm in the pressure range of 3.6-20.6 torr. The effects of added NO, H2S, and CF4 were investigated. The extinction coefficient at 147 nm and 296°K was determined to be 64 ± 8 atm-1 · cm-1.The molecule photodecomposes largely by α,β elimination of HCl to give 1,1-difluoroethylene (Φ = 0.74 ± 0.06). There is no observable elimination of HF, but there is strong evidence for the elimination of the elements of FCl though the relative importance of this process is minor, as are contributions from carbon—carbon and carbon—halogen bond fission.The 1,1-difluoroethylene formed is undoubtedly vibratonally excited and is the source of a pressure-dependent small yield of fluoroacetylene. Over the pressure range studied there is no evidence that the major primary process itself is affected by changes in total pressure as is the case in the 147-nm photolysis of ethyl chloride.
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  • 52
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
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    Topics: Chemistry and Pharmacology
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  • 53
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Arrhenius parameters for the reactions and have been measured. Reaction (2a) was generated and studied by the photolysis of tetrachloromethane in the presence of trichlorosilane and reaction(2b) by the photolysis of 1,1,1,-trichlorotrifluoroethane in the presence of trichlorosilane.The measured data are given by the expressions \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm log}_{{\rm 10}} k_{2{\rm a}}} & = & {11.06 - \frac{{8760}}{{4.57T}}} \\ {{\rm log}_{{\rm 10}} k_{2{\rm b}}} & = & {11.18 - \frac{{8980}}{{4.57T}}} \\ \end{array} $$\end{document} .
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  • 54
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    Topics: Chemistry and Pharmacology
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  • 55
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    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of perfluoro-di-t-butyl peroxide has been studied for the first time. The reaction was carried out in the gas phase between 5 and 600 torr in the 108-149°C temperature region. The products consisted solely of C2F6 and CF3COCF3. The decomposition was found to be first order and homogeneous. The rate constant is given by log kdecomp(sec-1) = (16.2 ± 1.2) - (148.7 4.4)/2.3RT where R is 0.008314kJ/mol · °K. These Arrhenius parameters are consistent with those determined for the decomposition of di-t-butyl peroxide.
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  • 56
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase pyrolyses of 2-chloro-3-methylbutane and pinacolyl chloride in the temperature range of 345-390°C and pressure range of 60-220 mm Hg are homogeneous and unimolecular in a seasoned reaction vessel. The temperature dependence of the rate constants is given by the Arrhenius equations \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}\,k_{\rm 1} ({\rm sec}^{- 1}) = (13.80 \pm 0.24) - (49,700 \pm 700){\rm cal}/{\rm mol}/2.303RT $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}\,k_{\rm 1} ({\rm sec}^{- 1}) = (12.99 \pm 0.09) - (47,200 \pm 250){\rm cal}/{\rm mol}/2.303RT $$\end{document} respectively. The Wagner-Meerwein rearrangement was not observed in these eliminations. Some correlations for the pyrolysis of α-substituted alkyl chlorides are presented and discussed. These facts are consistent with the heterolytic nature of the cyclic transition state mechanisms for these reactions.
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  • 57
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    Topics: Chemistry and Pharmacology
    Notes: NO Abstract.
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  • 58
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  • 59
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The unimolecular decomposition of 3,3-dimethylbut-1-yne has been investigated over the temperature range of 933°-1182°K using the technique of very low-pressure pyrolysis (VLPP). The primary process is C—C bond fission yielding the resonance stabilized dimethylpropargyl radical. Application of RRKM theory shows that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by log (k/sec-1) = (15.8 ± 0.3) - (70.8 ± 1.5)/θ where θ = 2.303RT kcal/mol. The activation energy leads to DH0[(CH3)2C(CCH)—CH3] = 70.7 ± 1.5, θH0f((CH3)2ċCCH,g) = 61.5 ± 2.0, and DH0[(CH3)2C(CCH)—H] = 81.0 ± 2.3, all in kcal/mol at 298°K. The stabilization energy of the dimethylpropargyl radical has been found to be 11.0±2.5 kcal/mol.
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  • 60
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the reaction of cis-(NO)2 with solid oxygen to form iso-N2O4 have been studied between 13 and 29 K. The overall reaction is pseudo first order in cis-(NO)2, and solid oxygen serves both as a reactant and the matrix. The pseudo-first-order rate constants are calculated to be k(14N) = 4.25 × 10-2 exp(-103/RT), and k(15N) = 3.00 × 10-2 exp(-105/RT) sec-1, based on temperature measurements from a thermocouple junction which may be at most three degrees lower than the actual reacting film. Most significantly, however, 14k/15k = 1.55 at∼13 K. The condensed phase reaction has been compared to that observed in the gas phase, and the extremely small pre-exponential factors and large isotope effects have been discussed in terms of tunneling corrections and orientational constraints. It is suggested that the form of the crystal plays an integral role in the observed process.
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  • 61
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of the interaction of Cu+-α,α-dipyridyl complex (Cu+L2) with O2 in both neutral and acid media was studied by the stopped-flow method. The dependence of the mechanism on the acidity of the medium was established. In an acid medium H+ participated in a direct O2 reduction to HO2 by interaction with an oxygen adduct L2Cu+O2 formed without displacement of ligand molecules. In a neutral medium the reaction rate was limited by inner sphere charge transfer from Cu+ to O2 to form an oxygen “charge transfer” complex L2CuO+2. The latter interacted either with the second ion Cu+L2 or with the free ligand, or else it dissociated, reversibly or irreversibly, to form a radical anion O-2. The bimolecular rate constants of the oxygen “adduct” and “charge transfer” complex formation appeared to be kbi = (1.0 ± 0.1) × 105 and (1.5 ± 0.2) × 104M-1ċsec-1, respectively. The effective termolecular rate constants of O2 reduction to HO2 in an acid medium (with contribution from H+) and to O-2 in a neutral medium (with contribution from α,α-dipyridyl) were kter = 2.7 × 108 and 107M-2ċsec-1. The rate constants of the elementary steps were estimated. The auto-oxidation mechanism of the aquoion and complexes of Cu+ is discussed in terms of the results obtained.
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  • 62
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ferric oxide has been found to promote both the ketonization of acetic acid and its esterification with methyl alcohol, isopropyl alcohol, and benzyl alcohol. The competitive kinetic technique, where the esterification reaction is made to compete with the ketonization of acetic acid, has been used to elucidate the mechanistic model for the ketonization of acetic acid on iron oxide. The ketonization of acetic acid at 375°C is found to be a second-order reaction which proceeds through a Langmuir-Hinshelwood mechanism.
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  • 63
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal gas-phase decomposition of vinyl chloride has been studied behind shock waves over the temperature range of 1350-1900°K and the density range of 7 × 10-7-1.5 × 10-3 mol/cm3 (at 1600°K) in mixtures of C2H3Cl highly diluted with argon. The ultraviolet absorption of C2H3C was recorded at 230 nm as a function of time. The decomposition proceeds via molecular elimination of HCl. The unimolecular dissociation rate is pressure dependent at all but the highest pressures applied. Application of modified HKRR theory results in the rate expression \documentclass{article}\pagestyle{empty}\begin{document}$$ k_\infty = 10^{14.0 \pm 0.2}\, {\rm exp}[= (290 \pm 12){\rm kJ}/{\rm mol}/RT]\,{\rm s}^{- 1},\,\quad 1400^ \circ {\rm K} \le T \le 1800^ \circ {\rm K} $$\end{document} for the limiting high pressure rate constant, and in a collision efficiency of \documentclass{article}\pagestyle{empty}\begin{document}$$ \beta _c = \frac{{k_0 ({\rm experiment})}}{{k_{\rm 0} {\rm (theoretical, strong collisions})}} \cong 0.04,\quad {\rm for M} = {\rm Ar},T = 1600^ \circ {\rm K} $$\end{document} derived from the limiting low-pressure rate constant.
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  • 64
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics and stoiehiometry of the decomposition of N2H2 and N2D2 have been studied as a function of sample size, pressure, and temperature. The reaction follows a single first order kinetic expression over most of its time course. It is suggested that the rate-determining step in the mechanism is a first-order homogeneous gas-phase isomerization of trans-diimide with rate constants:kN2H2 = 1.8 exp (-4.2 kcal/mol/RT) sec-1 and kN2D2 = 1 exp (-4.4 kcal/mol/RT) sec-1. The detailed mechanism of this isomerization, however, is not evident. At temperatures above room temperature, self-heating has been observed which leads to an initial fast decay. At room temperature the reaction exhibits autocatalysis with the rate increasing as the reaction proceeds. This has been attributed to enhancement by a surface decay process involving adsorbed hydrazine.The only significant products from the decomposition of N2H2 are N2, H2, and N2H4, and the results are interpreted in terms of two parallel reactions: The decomposition of N2D2 occurs almost completely by the single reaction giving N2 + N2D4. No azide formation has been detected from either N2D2, or N2D2, and limits have been put on the yield of ammonia. Extinction coefficients at 365 nm of 3.9 ± 0.2 for N2H2 and 3.3 ± 0.1 for N2D2 have been measured.Both the rate of decay and the stoichiometry of products show pressure dependence below 150 torr, and this is suggested to be due to direct decomposition of cis-N2H2 on the surface.
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  • 65
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equilibrium has been studied between 275°and 363°K. Third-law calculations lead to ΔH°298(1) = -11.50 ±0.17 kcal/mol, from which \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} \Delta H_{{\rm f}298}^ \circ ({\rm BrNO},g) = 19.52 \pm 0.24\,{\rm kcal}/{\rm mol} \\ D_0^ \circ ({\rm Br - NO}) = 27.90 \pm 0.30\,{\rm kcal}/{\rm mol} \\ \end{array} $$\end{document}Absorption bands of BrNO in the ultraviolet with e (γmax = 215 nm) = 1.84±0.17 × 104 1/mol·cm, and in the red with e (γmax = 708 nm) = 7.7±1.9 1/mol·cm at 298°K have been investigated.The rate of formation of BrNO has also been measured between 275°and 363°K.
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  • 66
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurements of the NO-catalyzed dissociation of I2 in Ar in incident shock waves were carried out in the temperature range of 700°-1520°K and at total concentrations of 5 × 10-6-6 × 10-5 mol/cm3, using ultraviolet-visible absorption techniques to monitor the disappearance of I2. It was shown that the main reaction responsible for the disappearance under these conditions is I2 + NO → INO + I, for which a rate coefficient of (2.9 ± 0.5) × 1013 exp[-(18.0 ± 0.6 kcal/mol)/RT] cm2/mol·sec was determined. The INO formed dissociates rapidly in a subsequent reaction. The reaction, therefore, constitutes a “chemical model” for a “thermal collisional release mechanism.” Preliminary measurements of the rate coefficient for I2 + NO2 → INO2 + I are also presented. Combined with information on the reverse reactions obtained in earlier room temperature experiments, these results lead to accurate values of ΔH°f for INO and INO2 equal to 29.7 ± 0.5 and 15.9 ± 1 kcal/mol, respectively.
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  • 67
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 68
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The temperature dependence of the vibration-vibration energy transfer between the v3 mode of 15N14NO and the first vibrational level of CO was determined over a range of 680 to 1300°K using a shock tube. Several mixtures of 15N14NO—CO were tested, diluted in 95% Ar. The resulting exothermic transfer probabilities for the reaction, \documentclass{article}\pagestyle{empty}\begin{document}$$ ^{15} {\rm N}^{14} {\rm NO}(001) + {\rm CO}({\rm O}) \to ^{15} {\rm N}^{14} {\rm NO}(000) + {\rm CO}(1) $$\end{document} are compared to previous work on N2O - CO. The results for 15N14NO—CO exhibit a more pronounced direct temperature dependence than for N2O - CO even though the process has a closer resonance (ΔE = 59 cm-1 for 15N14NO—CO and ΔE = 81 cm-1 for N2O—CO).
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  • 69
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO2 to determine rate constants k1 and k2 in the temperature range of 391-432°K: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm DMP}} & \stackrel{1}{\longrightarrow} & {2{\rm MeO}} \\ {{\rm MeO + DMP}} & \stackrel{2}{\longrightarrow} & {{\rm MeOH + CH}_{\rm 2} {\rm O} + {\rm MeO}} \\ \end{array} $$\end{document} The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k1(sec-1) = (15.7 ± 0.5) - (37.1 ± 0.9)/2.3 RT and k2 ≈ 5 × 104M-1· sec-1. The disproportionation/recombination ratio k7b/k7a = 0.30 ± 0.05 was also determined: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm MeO} + {\rm NO}_2 (+ {\rm M})} \stackrel{7a}{\longrightarrow} & {{\rm MeONO}_{\rm 2} (+ {\rm M})} \\ {{\rm MeO} + {\rm NO}_2} \stackrel{7b}{\longrightarrow} & {{\rm CH}_{\rm 2} {\rm O} + {\rm HONO}} \\ \end{array} $$\end{document}When O2 was added to DMP mixtures containing NO2, relative rate constants k12/k7a were obtained over the temperature range of 396-442°K: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} {{\rm CH}_{\rm 3} {\rm O} + {\rm O}_2} \stackrel{12}{\longrightarrow} & {{\rm CH}_2 {\rm O} + {\rm HO}_{\rm 2}} \\ \end{array} $$\end{document} A review of literature data produced k7a = 109.8±0.5M-1·sec-1, giving log k12(M-1·sec-1) = (8.5 ± 1.5) - (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments.
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