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  • Physical Chemistry  (205)
  • Wiley-Blackwell  (205)
  • Cambridge University Press
  • 1980-1984  (123)
  • 1975-1979  (82)
  • 1981  (123)
  • 1975  (82)
Collection
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  • Wiley-Blackwell  (205)
  • Cambridge University Press
Years
  • 1980-1984  (123)
  • 1975-1979  (82)
Year
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 7 (1975), S. 1-13 
    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 N2O and the first vibrational level of CO was determined over a range of 780 to 1400°K using a shock tube. Several mixtures of CO-N2O were tested, diluted in 95% Ar. The Landau-Teller plot of the vibration-vibration relaxation times has a least squares line of \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} p\tau _{{\rm VV}} = 2.69T^{ - 1/3} - 1.70 $$\end{document} where pτvv is in atm ·μsec and T in °K. The measured kinetic reaction was determined to be \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm N}_{\rm 2} {\rm O(001) + CO(O)} \to {\rm N}_{\rm 2} {\rm O}(000) + {\rm CO(1) + 81cm}^{{\rm - 1}} $$\end{document} The transfer probabilities for this process were found to vary directly with temperature.
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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 activation energy parameters for the reaction of PdX42- (X=Cl-, Br-) in aqueous halide acid solution with thiourea (tu) and selenourea (seu) have been determined. High rates of reaction parallel low enthalpies and appreciable negative entropy of activation. The rate law in each case simplifies to kobs=k[L] where L=tu or seu, and only ligand-dependent rate constants are observed at 25°C. The ligand-dependent rate constants for the first identifiable step in the PdCl42- + X system is (9.1±0.1) × 103 M-1 sec-1 and (4.5±0.1) × 104 M-1 sec-1 for X=tu and seu, respectively, while for the PdBr42- + X system it is (2.0±0.1) × 104 M-1 sec-1 and (9.0±0.1) × 104 M-1 sec-1 for X=tu and seu, respectively.
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  • 3
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 7 (1975), S. 125-142 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A detailed shock-tube investigation of the ignition in H2 + Cl2 + Ar mixtures in a shock tube is presented, and the mechanism of the reaction is discussed. Ignition delay times were determined from pressure and heat flux measurements behind reflected shock waves. The induction times measured ranged between 35 and 2100 μsec over the temperature range of 830-1260°K. The experimental results of close to seventy tests can be correlated by the relationship \documentclass{article}\pagestyle{empty}\begin{document}$$ t_{{\rm ig}} = 10^{ - 12.73} \exp (18.75 \times 10^3 /RT) \cdot [{\rm Cl}_{\rm 2}]^{ - 0.66} [{\rm H}_{\rm 2}]^{ - 0.60} [{\rm Ar]}^{{\rm 0}{\rm .40 }} \,\sec. $$\end{document} where the concentrations are expressed in mole/cm3. The above relationship served as a basis for a computer modeling of the ignition delay times. Ten calculations, simulating typical laboratory experiments, were run by the computer for each reaction scheme and the obtained temperature and composition dependence of the induction times were compared with the ones observed experimentally. A reaction scheme based on a simple exothermal chain propagation could not reproduce the experimental relationship. When the energy branching reaction HCl*(ν) + Cl2 → (HCl3) → HCl + Cl + Cl was added to the reaction scheme, a much better agreement with the experiment was obtained. It is believed that the above reaction does take place and that it is the main supplier of atoms to the system.
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  • 4
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 7 (1975), S. 205-214 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spectrophotometric methods have been used to obtain rate laws and rate parameters for the following reactions: with ka, kb, Ea, Eb having the values 85±5 l./mole · s, 5.7±0.2 s-1 (both at 298.2°K), and 56±4 and 66±2 kJ/mole, respectively. with kc=0.106±0.004 l./mole ·s at 298.2°K and Ec=67±2 kJ/mole. with kd=(3.06 ±; 0.15) × 10-3 l./mole ·s at 298.2°K and Ed=66±2 kJ/mole.Mechanisms for these reactions are discussed and compared with previous work.
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  • 5
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 7 (1975), S. 249-272 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of decarbonylation of [Ir(CO)(dp)2]Cl and [IrCl(CO)2(Ph3P)2] has been studied in different solvents, at temperatures between -25° and +70°C, by means of reactors of defined fluid dynamics which allow a separation to be made between “physical” and “chemical” rate constants. Chemical rate constants have been found to depend markedly on the diffusion coefficients of carbon monoxide in the various solvents. The process of decarbonylation has been described, for both reactions, by the sequence: structural isomerization, characterized by a very low preexponential factor, decomposition of the less stable isomer against the solvent's barrier, and diffusion of carbon monoxide to the gas-liquid interface. The kinetic problems involved in the determination of rate constants and their implications have been emphasized.
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  • 6
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 7 (1975), S. 287-300 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The overall photobromination reactions \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Br}_{\rm 2} + {\rm R}_{\rm F} {\rm I} \to {\rm IBr} + {\rm R}_{\rm F} {\rm Br} $$\end{document} have been studied using a competitive technique. Relative Arrhenius parameters were obtained for the rate-determining step These were placed on an absolute basis using previous-absolute values of A and E for RFI=CF3I. The activation energies were used to calculate bond dissociation energies D(R—I) with the following results: TextRF-E16D(RF-I)(kcal/mole)CF3I10.852.6C2F5I8.850.6n-C3F7I7.449.2i-C3F7I7.549.2n-C4F9I6.748.4E16 from [1]The D(RF-I) are compared with related D(R—I) and it is concluded that for a given alkyl group RH and the corresponding perfuloroalkyl group RF, D(RH-I) 〉 D(RF-I) whereas it has previously been found that D(RH-X;) 〈 D(RF-X) where X is not iodine.
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  • 7
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    International Journal of Chemical Kinetics 7 (1975), S. 341-349 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of reaction of t-BuOOK, t-BuOK, n-BuOOK, and p-MeC6H4OKwith p-nitrophenyl diphenylphosphinate 1 and with p-nitrophenyl benzoate 2 have been measured in toluene both in the absence and in the presence of crown polyether dicyclohexyl-18-crown-6 3a. The rates of nucleophilic displacementon 1 by HOO-, t-BuOO-, and some “nonalpha” oxyanions in water have also been determined. Solvent transfer from water to toluene results in increasing the nucleophilic reactivity of the t-butyl hydroperoxide anion. Rate ratios QQa are given which allow one to estimate the enhanced reactivity of t-BuOO- (an α-nucleophile) compared to oxygen nucleophiles of comparable base strength toward 1 and 2. These are for substrate 1, Qα (water) ≃ 6.5 and Qα (toluene) ≃ 2.7; for substrate 2, Qα (water) ≃ 5.5 and Qα (toluene) ≃ 5. The hypothesis is advanced that solvation is not a major factor in determining the α-effect of the t-butylhydroperoxide anion.
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  • 8
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    International Journal of Chemical Kinetics 7 (1975), S. 633-636 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 9
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 7 (1975) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 10
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    International Journal of Chemical Kinetics 7 (1975), S. 463-471 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A consecutive single-route reaction is considered. When two (groups of) steps compete in controlling the overall reaction rate, there exists a general rule that the earlier step in the flow of the overall reaction tends to be rate-determining with the increase of the reaction affinity. The latter may, however, be distributed more or less evenly to both steps.
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  • 11
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    International Journal of Chemical Kinetics 7 (1975), S. 479-507 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanisms of the pyrolyses of the n-alkanes C3H8, n-C4H10, and n-C5H12 at temperatures between 390 and 560°C have been studied by the construction and evaluation of sets of several hundred reactions. Rate parameter values were assigned using literature data and calculated estimates. Time-dependent numerical solutions were computed for the experimental conditions of several rate and product studies reported in the literature. The comparisons of these a priori computations with experiment show excellent agreement for propane and agreement for butane and pentane within the estimated error limits of the assigned rate parameters. These results demonstrate that the general “state of knowledge” of the mechanism of alkane pyrolysis, namely, the reactions and their rate parameters, is such that reasonable a priori predictions of experimental results can be made. Discussions of the major stepwise processes in the pyrolyses are presented, and the importance of allyl radicals in termination is demonstrated.
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  • 12
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    International Journal of Chemical Kinetics 7 (1975), S. 547-555 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The decomposition rate of chemically activated ethyltrimethylgermane from the reaction 1CH2 + (CH3)4Ge, where 1CH2 was produced from diazomethane photolysis at 3660 Å, is 8.6 × 105 sec-1. This result combined with RRKM theory and critical energy estimates yields an Arrhenius A factor of log[A (sec-1)/methyl] = 14.7 ± 0.8 for methyl rupture from germanium.Log A values for methyl rupture from carbon, silicon, and germanium linearly correlate with the vibrational-rotational entropies of the corresponding tetramethyls. Extrapolation predicts log[A (sec-1)/methyl] = 14.4 and 14.3 for methyl rupture from tin and lead, respectively.
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  • 13
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    International Journal of Chemical Kinetics 7 (1975), S. 625-631 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of methoxy radicals to several olefins has been studied by a competitive method at 127°C in gas phase. The thermal decomposition of dimethyl peroxide was used as methoxy radical source. The rate of addition to the double bond was measured relative to the oxidation of carbon monoxide. For the addition to ethylene it was obtained that \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{{\rm add}} = \left({3.7 \pm 0.8} \right) \times 10^4 M^{ - 1} \cdot {\rm s}^{{\rm - 1}} $$\end{document} This rate constant is similar to the one shown by methyl radicals under similar conditions. From the relative rate of addition to several chlorinated and fluorinated olefins it can be concluded that methoxy radicals show very little “electrophilic” character.
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  • 14
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    International Journal of Chemical Kinetics 13 (1981), S. 135-148 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate of the cerium (IV) oxidation of p-chloromandelic acid has been studied in perchlorate media at an ionic strength of 1.50 mol/dm3 by the stopped-flow technique and in H2SO4—MHSO4 (M+ = Li+, Na+, K+) and H2SO4—MClO4 (M+ = H+, Li+, Na+) mixtures at constant total electrolyte concentrations of 1.00 and 2.00 mol/dm3 using the conventional spectrophotometric method. In perchlorate media the kinetic data indicate the formation of two intermediate complexes between cerium (IV) and the organic substrate, but only one is significantly involved in the intramolecular electron-transfer process. The oxidation rate is markedly lower in sulfate media, where two reaction paths have been found to contribute to the overall redox reaction. The univalent cations examined exhibit negative specific effects upon the overall oxidation rate increasing in the order H+ 〈 Li+ 〈 Na+ 〈 K+. Activation parameters have been also estimated.
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  • 15
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 13 (1981) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 16
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    International Journal of Chemical Kinetics 13 (1981), S. 231-243 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spectrum of the intermediate product ascribed to nitrosopentane has been detected in the photolysis of the SO2-pentane (RH)-NO mixture. This result has been interpreted in terms of the radical mechanism by assuming the H-atom abstraction from RH by the excited SO2 molecules to be the primary act. The contribution of the singlet and triplet SO2 states to the product formation rate and the ratio of the singlet-to-triplet rate constants have been evaluated. At NO pressures above 5 torr, the product formation rate significantly deviates from the Stern-Volmer dependence.
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  • 17
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    International Journal of Chemical Kinetics 13 (1981), S. 325-332 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction Cl + H2CO → HCl + HCO has been studied at 295 K. Chlorine atoms were produced via the infrared laser induced dissociation of CCl3F, using a pulsed CO2 TEA laser. Using HCl infrared chemiluminescence as the diagnostic, we find the rate constant to be 7.4 ± 0.7 × 10-11 cm3/molecule sec, in good agreement with several recent studies. An evaluation of TEA laser photolysis as a technique for the generation of chlorine atoms is made, and the relationship of this experiment to recent theories of infrared laser induced chemistry is discussed.
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  • 18
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    International Journal of Chemical Kinetics 13 (1981), S. 385-401 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the reaction have been investigated in H2SO4 medium under different conditions. The observed bimolecular rate constant kobs, has been found to depend on [H+]-0.55 and to increase with the initial concentration ratio of the reactants R0 = [H2O2]0/[U (IV)]0 above 0.49. The activation energy of the overall reaction has been determined as 13.79 and 14.3 kcal/mol at R0 = 1 and 0.35, respectively. Consistent with experimental data, a detailed reaction mechanism has been proposed where the hydrolytic reaction (4) followed by the rate-controlling reaction (10) and subsequent fast reactions of U (V) and OH radicals are involved: A kinetic expression has been derived from which a graphical evaluation of (kK4)-1 and k-1 has been made at R0 = 1 as (12.30 ± 0.09) × 10-3 M min, (6.23 ± 2.19) × 10-4 M min; and at R0 = 0.35 as (12.63 ± 2.13) × 10-3 M min, (8.32 ± 6.62) × 10-4 M min, respectively. Indications of some participation of a chain reactionat R0 = 1 have been obtained without affecting thesecond-order kinetics as observed.
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  • 19
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    International Journal of Chemical Kinetics 13 (1981) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 20
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    International Journal of Chemical Kinetics 13 (1981), S. 433-444 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No reliable rate constant is available for the self-reaction of tert-;butoxy radicals. We have set up a competition between hydrogen abstraction and self-reaction of tert-butoxy radicals in a flash photolysis electron spin resonance study to extract this information. Experimental values of hydrogen abstraction product radical concentrations under various hydrogen donor concentrations were then compared with theoretically calculated values with different values of 2k4 to obtain the best fit. Hydrogen donors such as cyclopentane, anisole, methyl tert-butyl ether, and methanol were chosen for the study. A value of (1.3 ± 0.5) × 109M-1 sec-1 for the rate constant of the self-reaction of tert-butoxy radicals has been determined at 293°K.
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  • 21
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    International Journal of Chemical Kinetics 13 (1981), S. 481-495 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of ethane has been reinvestigated using the single pulse, reflected shock technique. Reflected shock temperatures were corrected for boundary layer-induced nonidealities using the thermal decomposition of cyclohexene as a kinetic standard. The rate constant for the reaction was calculated from the rate of formation of methane under conditions of very low extent of reaction, over a temperature range of 1000-1241 K. Ethane compositions of 1% and 3% in argon at total reaction pressures of 3 and 9 atm were used, and a small pressure dependence of k1 was observed.An RRKM model is described which gives excellent agreement with this and other recent dissociation and recombination rate constant data in light of a recent revision to the thermochemistry of the methyl radical. In the range of 1000-1300 K an RRKM extrapolated k1∞ is given by the expression, log k1∞ = 17.2 - 91,000/2.3RT, while at 298 K the calculation gives log k-1∞ (l/mol sec) = 10.44, where k-1∞ is calculated from k1∞ and the equilibrium constant.
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  • 22
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    International Journal of Chemical Kinetics 13 (1981), S. 503-514 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title reaction has been investigated in the temperature range of 494-545 K. During the early stages of reaction the only observed products were silyl iodide and hydrogen iodide. Initial rates were found to obey the rate law over a wide range of initial iodine and monosilane pressures. Secondary reactions, most probably of SiH3I with I2, became more important as the reaction progressed. However, provided [SiH4]0/[I2]0 〉 20, these secondary processes had a negligible effect on the kinetics, and an integrated rate expression could be used. These kinetics are consistent with an iodine atom abstraction chain mechanism, and for the step has been deduced. From this the bond dissociation energy D(SiH3—H) = 378 ± 5 kJ/mol (90 kcal/mol) is obtained. The kinetic and thermochemical implications of this value, especially to the pyrolysis of monosilane, are discussed.
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  • 23
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    International Journal of Chemical Kinetics 13 (1981), S. 591-601 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that A factors for atom fissions in polyatomics can be reliably estimated by an improved version of the restricted free rotor model (RFRM). No adjustable parameters are used in the evaluation of A factors for the dissociation of the RO—F bond (R: NO2, SF5, CF3, FSO2), and the authors' predictions are compared with high-pressure kinetic data for these reactions. In the case of O2NOF, for which full spectroscopic information is available, RFRM reproduces the observed value Am well within a factor of 2. Similar agreement is reached for F5SOF and FO2SOF, assigning reasonable limits to their —OF torsional frequencies. For F3COF, Am and the calculated back reaction rate constant, which is independent of the model, are both much too small to be plausible, suggesting falloff effects rather than a failure of RFRM.
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  • 24
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    International Journal of Chemical Kinetics 13 (1981), S. 627-638 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bis(trifluoromethyl) peroxide is readily dissociated by multiple infrared photon excitation at CO2 laser wavelengths. The primary dissociation product is CF3O; approximately 85% of the nascent radicals are further dissociated in the laser field to form CF2O and F. The F atoms then react with the remaining CF3O to produce CF3OF. The formation of CF3OF is strongly inhibited by addition of HI, which reacts preferentially with the F atoms.
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  • 25
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    International Journal of Chemical Kinetics 13 (1981), S. 695-705 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The acid-catalyzed enolization of acetone in the presence of bromine is found to be catalyzed by the anionic micelles of sodium dodecyl sulfate. The rate acceleration expected on the basis of lowering of activation energy is largely nullified by the decrease in the entropy of activation, leading to a very small rate enhancement, i.e., kψ/k0 = 1.2 at 30°C. The binding constant for the micelle-substrate complex is determined. The micellar rate enhancement is the same, irrespective of the halogen used, chlorine, bromine, or iodine.
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  • 26
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    International Journal of Chemical Kinetics 7 (1975) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 27
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    International Journal of Chemical Kinetics 7 (1975), S. 33-37 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present study reports the measurement of the V-V energy transfer rates for the CO*—COS system in the temperature range of 195 to 370°K. The measured rates exhibit a slight inverse temperature dependence. The experimental results are compared to prediction based on a model of long-range dipole-dipole interactions between colliding molecules. The effect of single quantum rotational transitions is compared to that of multiquantum rotational transitions.
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  • 28
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    International Journal of Chemical Kinetics 7 (1975), S. 77-86 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electronically excited tin atoms Sn(51D2), 1.068 eV above the 53P0 ground state, have been generated by the pulsed irradiation of tin tetramethyl and monitored photoelectrically in absorption by time-resolved attenuation of atomic resonance radiation at λ=285.06 nm [Sn((5d3F20) ← (5p2 1D2))]. Deactivation rate constants are reported for the quenching of Sn(51D2) with a range of collision partners and the resulting data are compared with those for analogous states within group IV, namely, C(21D2) and Pb(61D2). The data are discussed in terms of correlations based on both the weak and strong spin orbit coupling approximations.
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  • 29
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With a continuous jet-stirred tank reactor operating at small space time (0.05-1.2 s) the kinetics of the formation of six minor products (ethane, isobutane, butene-1, 2,3-dimethyl-butane, 4-methylpentene-1, and 1,5-hexadiene) are studied during the pyrolysis of propane, at small extents of reaction and over the temperature range of 600-780°C. The experimental results are in agreement with the free radical mechanism proposed by Jezequel, Baronnet, and Niclause for this reaction. They show that the two most important termination processes are The measured rates of formation of the minor products are consistent with the quasi-identical values estimated by Jezequel and co-workers (between 475 and 505°C) and by Allara and Edelson (between 510 and 560°C) for kinetic parameters (A1 ≃ 1016.65 s-1 and E1 ≃ 84.7 kcal/mole) of the chain initiation process
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  • 30
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    International Journal of Chemical Kinetics 7 (1975), S. 661-677 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of acetylene by water vapor was studied behind the reflected shock in a single-pulse shock tube. Computer simulation experiments reproduced the experimental results in the temperature range of 1500 to 2000°K. The kinetic scheme suggested here involves three major processes, (1) production of hydrogen atoms by the sequence of reactions which lead from acetylene to carbon; (2) production of OH radicals, mainly by the reaction H + H2O → H2 + OH, and (3) fast oxidation of the acetylene and other C/H species by the available oxidants in the system. The experimental results of methane oxidation suggest that methane is converted to acetylene prior to its oxidation. The implication of the experimental results to processes occurring in planetary atmospheres as a result of thunder shock waves is briefly discussed.
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  • 31
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    International Journal of Chemical Kinetics 7 (1975), S. 443-451 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equilibrium quotients for the formation of Co(NH3)5Cl2+ from Co(NH3)5OH23+ and Cl- were 3.74±0.25 M-1 and 6.07±0.54 M-1 at 45.0°C in 10:1 mole ratio water: dimethyl sulfoxide and in 25 w/w % aqueous ethanol, respectively, and those forthe formation of the ion pair Co(NH3)5OH23+ . Cl- were 1.21±0.20 M-1 and 1.58±0.17 M-1, respectively, in the same solvents. The aquation and anation rateconstants were determined at 45.0°C for these two solvents over the range of chloride-ion concentrations 0.0 ≤ [Cl-] ≤ 0.9 M. The aquation rate constant was essentially independent of chloride-ion concentration in each solvent over this range. The inverse of the pseudo-first-order anation rate constant was linearly dependent on the inverse of the chloride-ion concentration in each solvent. The least squares relationships between (1/kan) and (1/[Cl-]) gave intercepts and ratios of intercept to slope which were analyzed interms of Id and D mechanisms. It was concluded that the data were not satisfied by a D mechanism, but that they were consistent with an Id mechanism.
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  • 32
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    International Journal of Chemical Kinetics 7 (1975), S. 535-546 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction between a hydroquinone aqueous solution and manganese dioxide has been investigated by electron paramagnetic resonance spectroscopy. A very stable p-benzosemiquinone anion is formed when an aqueous solution of hydroquinone is passed through a column of manganese dioxide. The kinetics for the reaction between hydroquinone and manganese dioxide follow the equation \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{dC}}{{d\left({W/F} \right)}} = k_1 ^0 \left({A_0 - C} \right) - k_2 ^0 C $$\end{document} where A0 is the initial concentration of hydroquinone, C is the concentration of p-benzosemiquinone anions, W is the amount of manganese dioxide, F is the feed rate of a hydroquinone aqueous solution, and k10 and k20 are constants; k10 = 3.1 × 10-2 (cm3/g MnO2· min), k20 = 3.2 (cm3/g MnO2·min).A mechanism for the reaction is proposed such that Mn(IV) in manganese dioxide is reduced to Mn(II) with hydroquinone from which the semiquinone anion is formed via a neutral semiquinone. The formation of semiquinone anions from several substituted hydroquinones is also discussed.
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  • 33
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    International Journal of Chemical Kinetics 7 (1975), S. 575-587 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent-solute interactions in the peroxyacid oxidations are believed to be specific rather than electrostatic in nature. The kinetic solvent effects reported for the oxidations of organic sulfides, olefins, acetylenes, nitrosobenzenes, thioketones, and aryl sulfines reveal that in each case the rates are fast in nonbasic solvents (e.g., benzene, nitrobenzene, and halogenated hydrocarbons) relative to those in basic solvents such as DMF, dioxane, and alcohols. The rates in CF3CH2OH and aqueous or partially aqueous media are again higher than those in the basic solvents. This remakably similar pattern of sensitivity of rates to changes in the solvent nature appears to be characteristic of these oxidations as demonstrated by the existence of linear free-energy relationship. The behavior is best understood in terms of cyclic transition states for these oxidations in which charge separation is avoided by intra- or intermolecular hydrogen bonding depending on the nature of the solvent. Solvent effects on sulfoxide oxidation and on oxidations by hydrogen peroxide and t-butylhydroperoxide are also briefly discussed.
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  • 34
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    International Journal of Chemical Kinetics 7 (1975), S. 637-638 
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 35
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    International Journal of Chemical Kinetics 7 (1975), S. 679-688 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pyrolysis of tetrafluorohydrazine has been studied from 578 to 791°K. The stoichiometry has been established as \documentclass{article}\pagestyle{empty}\begin{document}$$ 6{\rm NF}_{\rm 2} \to 4{\rm NF}_{\rm 3} + {\rm N}_{\rm 2} $$\end{document} Reaction rates have been measured and the effects of surface area, inert gas pressure, and nitric oxide have been examined. The rate-determining step proposed is \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm 2NF}_{\rm 2} \to {\rm NF}_{\rm 3} + {\rm NF} $$\end{document} and the general rate expression obtained for this is \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = 10^{9.0 \pm 0.4} \exp {{ - 36,950 \pm 500} \mathord{\left/ {\vphantom {{ - 36,950 \pm 500} {RTM^{ - 1} \cdot \sec ^{ - 1} }}} \right. \kern-\nulldelimiterspace} {RTM^{ - 1} \cdot \sec ^{ - 1} }} $$\end{document}
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  • 36
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The high-pressure absolute rate constants for the decomposition of nitrosobenzene and pentafluoronitrosobenzene were determined using the very-low-pressure pyrolysis (VLPP) technique.Bond dissociation energies of DH0(C6H5—NO) = 51.5 ± 1 kcal/mole and DH0 (C6F5—NO) = 50.5 ± 1 kcal/mole could be deduced if the radical combination rate constant is set at log kr(M-1·sec-1) = 10.0 ± 0.5 for both systems and the activation energy for combination is taken as 0 kcal/mole at 298°K. δHf0(C6H5NO), δHf0(C6F5NO), and δHf0(C6F5) could be estimated from our kinetic data and group additivity. The values are 48.1 ± 1, -160 ± 2, and - 130.9 ± 2 kcal/mole, respectively. C-X bond dissociation energies of several perfluorinated phenyl compounds, DH0(C6F5-X), were obtained from the reported values of δHf0(C6F5X) and our estimated δHf0(C6F5) [X = H, CH3, NO, Cl, F, CF3, I, and OH].
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  • 37
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    International Journal of Chemical Kinetics 7 (1975), S. 785-795 
    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 trichloromethyl groups of the haloethanes (XCCl3), CF3CCl3, CH3CCl3, C2Cl6, C2Cl5H, and CH2ClCCl3, 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: The error limits are the standard deviations from least mean square Arrhenius plots. It is shown that the neighboring group effect on the rate of chlorine atom abstraction from the trichloromethyl groups can be correlated with Taft polar substituent constants.
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  • 38
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    International Journal of Chemical Kinetics 7 (1975) 
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    Keywords: Chemistry ; Physical Chemistry
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  • 39
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The homogeneous exchange reaction between tetradeutero methane and ammonia was studied behind reflected shocks in a single-pulse shock tube over the temperature range of 1300-1800°K. The rate of production of CD3H at the early stages of the reaction in mixtures ranging between 1-4.5% NH3 and 1-4.3% CD4 in argon is given by d[CD3H]/dt=kb [CD4]0[NH3]0, where kb=8 × 1016 exp (-65.3 × 103/RT) cm3/mole·sec. This activation energy is considerably lower than the one that may be expected on the basis of a pure free radical mechanism. It is rationalized by C2D6 impurities in the methane. No clear answer can be obtained regarding the role of a four-center intermediate in this reaction.
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  • 40
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    International Journal of Chemical Kinetics 7 (1975), S. 879-894 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The specific decomposition rates of chemically activated methylcyclobutane produced from CH2(1A1) reaction with cyclobutane have been determined. CH2(1A1)was produced from ketene photolyses at 3340 and 3130 Å and from diazomethane photolyses at 4358 and 3660 Å. Comparisons of the excitation energies of the methylcyclobutane, determined by RRKM theory calculations, and the experimental results for the ketene systems, with thermochemically predicted maximum excitation energies, favor an Arrhenius A factor in the range of 5 × 1015 to 1 × 1016 sec-1 for methylcyclobutane. This result is consistent with (1) the comparison of RRKM theory calculations and the experimental unimolecular falloff for methylcyclobutane, (2) the comparison of experimental A factors for cyclobutane and other alkylcyclobutane decompositions, and (3) two out of three reported experimental A factors for methylcyclobutane. An analysis of these and previous results leads to a value of the CH2(1A1) ↔ CH2(3B1) energy splitting of 9±3 kcal/mole.
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  • 41
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    International Journal of Chemical Kinetics 7 (1975), S. 973-979 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decompositions of ethyl chloride, iso propyl chloride, and tertiary butyl chloride were studied in a static system in the pressure range of 0.1-300 torr. The following Arrhenius equations for the high-pressure limit were obtained: The pressure dependence of the first-order rate constant (falloff) for these three unimolecular dehydrochlorination reactions, starting with approximately equal kω values, by proper choice of temperature, is shifted to lower pressures with increasing molecular size:
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  • 42
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    International Journal of Chemical Kinetics 13 (1981), S. 39-58 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A small tubular reactor having an inner diameter of 1-2 mm andused as the source in a molecular beam apparatus is described in detail. This arrangement allows the study of fast reactions with reaction times smaller than 1 msec. The preexplosive reaction phase between F2 and H2 and CH4, respectively, is investigated to find out the initiation reactions. In the F2/H2 reaction, initiation is brought about by heterogeneous generation of F atoms or some other surface reaction. Evidence is also obtained for chain branching reactions. In the F2/CH4 case the dominant initiation reaction is the homogeneous reaction CH4 + F2 → CH3 + HF + F. The rate constant for the reaction between 300 and 400 K is 1012.3±0.3 exp[-47 ± 8 kJ/mol/RT] cm3/mol sec. The analysis of the experimental data also yields the rate constant for the propagation reaction CH3 + F2 → CH3 F + F, which is 1012.3±0.3 exp[-4.6 ±2.1 kJ/mol/RT] cm3/mol sec.
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  • 43
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    International Journal of Chemical Kinetics 13 (1981), S. 321-322 
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 44
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    International Journal of Chemical Kinetics 13 (1981), S. 463-471 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of thermal decomposition of ethyl, isopropyl, and t-butyl trifluoroacetates have been studied in the gas phase. In each case initial decomposition follows the normal ester route to give an olefin and trifluoroacetic acid, and elimination of hydrogen fluoride does not occur. However, trifluoroacetic acid is thermally unstable at ethyl and isopropyl ester decomposition temperatures, and further products result, including those from the difluorocarbene produced by decomposing trifluoroacetic acid. Placing a CF3 group at an ester's γ carbon increases the polarity of its transition state and decreases its thermal stability. The activation energies of the ethyl and isopropyl esters are lowered by 3.8 and 4.7 kcal/mol compared to the corresponding acetates, and the primary decomposition kinetics, which are homogeneous and of the first order, are expressed by α-Methylation enhances the reactivity of the trifluoroacetates, and the t-butyl ester, the transition state for which is sufficiently polar for heterogeneous decomposition to occur, shows signs of thermal instability at room temperature. The equilibrium was also investigated and gave ΔH° = +13,580 cal/mol and ΔS° = +31.07 gibbs/mol in the forward direction. The results obtained extend and support the known structure-rate correlations in the gas-phase elimination of esters.
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  • 45
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    International Journal of Chemical Kinetics 13 (1981), S. 445-462 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal unimolecular decomposition of ethylbenzene, isopropylbenzene, and tert-butylbenzene was studied using the very-low-pressure pyrolysis (VLPP) technique. Each reactant decomposed by way of β C—C bond homolysis, producing methyl radicals and benzyl or benzylic-type radicals. RRKM calculations show that the observed rate constants, when combined with thermochemical estimates, are consistent with the following high-pressure rate expressions: \documentclass{article}\pagestyle{empty}\begin{document}$ \log k(\sec ^{ - 1}) = 15.3 - (72.7/{\rm \theta)} $\end{document} for ethylbenzene between 1053 and 1234 K, \documentclass{article}\pagestyle{empty}\begin{document}$ \log k(\sec ^{ - 1}) = 15.8 - (71.3/{\rm \theta)} $\end{document} for isopropylbenzene between 971 and 1151 K, and \documentclass{article}\pagestyle{empty}\begin{document}$ \log k(\sec ^{ - 1}) = 15.9 - (69.1/{\rm \theta)} $\end{document} for tert-butylbenzene between 929 and 1157 K, where θ (kcal/mol) = 2.303RT. Resulting activation energies combined with heat capacity and heat of formation data led to the following dissociation enthalpies and enthalpies of formation at 298 K: DH° (øCH(CH3)—CH3) = 73.8 kcal/mol, ΔHf° (øÇCH(CH3)) = 39.6 kcal/mol, DH° (øC(CH3)2—CH3) = 72.9 kcal/mol, and ΔHf° (øÇ(CH3)2) = 32.4 kcal/mol. Derived high-pressure rate constants are in good accord with results of lower temperature toluene- and aniline-carrier experiments.
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  • 46
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    International Journal of Chemical Kinetics 13 (1981) 
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    Keywords: Chemistry ; Physical Chemistry
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  • 47
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    International Journal of Chemical Kinetics 13 (1981), S. 149-172 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Overall and detailed kinetic descriptions of the pyrolysis of C3H8 have been proposed as a result of a turbulent flow reactor investigation in the temperature range of 1110-1235 K and at atmospheric pressure. The overall reaction was described by a first-order rate expression with an activation energy of 58.65 kcal/mol and a preexponential factor of 3.2 × 1012 sec-1. This expression agrees with previously reported rate data. In addition, a kinetic mechanism involving 13 chemical species and 32 elementary reactions has been postulated to describe the kinetics. Experimental data from the present flow reactor experiments and from static vessel and shock tube experiments reported in the literature were used to verify the mechanism. Agreement over the temperature range of 800-1400 K and over the pressure range of 0.1-8.5 atm was obtained by adjusting three rate constants. Previously reported values for these rate constants appear to require reexamination. The reactions in question are the following: The sum of the rate constants for reactions (2a) and (2b) and the rate constant for reaction (23) are best represented by \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{2a} + k_{2b} = 10^{- 0.1} T^4 \exp (-8300/{\rm RT}){\rm cm}^3 /{\rm mol}\;{\rm sec} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{23} = 10^{14.55} \exp (-14,340/{\rm RT}){\rm cm}^3 /{\rm mol}\;{\rm sec} $$\end{document} which differ with the expressions in the literature.
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  • 48
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    International Journal of Chemical Kinetics 13 (1981), S. 209-217 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By measuring the rates of decay of ozone in a large excess of reactant, second-order rate constants have been obtained for the reactions of ozone with ethene, propene, but-1-ene, trans-but-2-ene, isobutene, hex-1-ene, cyclopentene, cyclohexene, isoprene, vinyl fluoride, 1,1-difluoroethene, cis-1,2-difluoroethene, trans-1,2-difluoroethene, trifluoroethene, tetrafluoroethene, and 2,5—dihydrofuran. The reactions have been studied in synthetic air at atmospheric pressure and at temperatures of 294 and 260 K. The rate constants and Arrhenius parameters are discussed in relation to existing kinetic data on ozone-alkene reactions.
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  • 49
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies of the unimolecular decomposition of 4-methylpent-2-yne (M2P) and 4,4-dimethylpent-2-yne (DM2P) have been carried out over the temperature range of 903-1246 K using the technique of very-low pressure pyrolysis (VLPP). The primary reaction for both compounds is fission of the C—C bond adjacent to the acetylenic group producing the resonance-stabilized methyl-substituted propargyl radicals, CH3C≡ĊH(CH3) from M2P and CH3C≡CĊ(CH3)2 from DM2P. RRKM calculations were performed in conjunction with both vibrational and hindered rotational models for the transition state. Employing the usual assumption of unit efficiency for gas-wall collisions, the results show that only the rotational model with a temperature-dependent hindrance parameter gives a proper fit to the VLPP data over the entire experimental temperature range. The high-pressure Arrhenius parameters at 1100 K are given by the rate expressions log k2 (sec-1) = (16.2 ± 0.3) - (74.4 ± 1.5)/θ for M2P and log k3 (sec-1) = (16.4 ± 0.3) - (71.4 ± 1.5)/θ for DM2P where θ = 2.303RT kcal/mol. The A factors were assigned from the results of recent shock-tube studies of related alkynes. Inclusion of a decrease in gas-wall collision efficiency with temperature would lower both activation energies by ∼1 kcal/mol. The critical energies together with the assumption of zero activation energy for recombination of the product radicals at 0 K lead to DH0[CH3CCCH(CH3)—CH3] = 76.7 ± 1.5, ΔHf0[CH3CCCH(CH3)] = 65.2 ± 2.3, DH0[CH3CCCH(CH3)—H] = 87.3 ± 2.7, DH0[CH3CCC(CH3)2—CH3] = 72.5 ± 1.5, ΔHf0[CH3CCĊ(CH3)2] = 53.0 ± 2.3, and DH0[CH3CCC(CH3)2—H] = 82.3 ± 2.7, where all quantities are in kcal/mol at 300 K. The resonance stabilization energies of the 1,3-dimethylpropargyl and 1,1,3-trimethylpropargyl radicals are 7.7 ± 2.9 and 9.7 ± 2.9 kcal/mol at 300 K. Comparison with results obtained previously for other propargylic radicals indicates that methyl substituents on both the radical center and the terminal carbon atom have little effect on the propargyl resonance energy.
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    International Journal of Chemical Kinetics 13 (1981), S. 283-293 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is assumed that A∞ in the limiting high-pressure unimolecular rate constant expression k∞ = A∞ exp(-Ea∞/kT) is given by A∞ = A″∞eBkT. The test case is the decomposition butane → 2 ethyl, where a negative B reproduces the temperature dependence of A∞ about as well as the previously considered power law A∞ = A′∞(kT)n. It is shown that the term eBkT modifies significantly the high-temperature falloff of the general-pressure rate constant kuni and its various derivatives, and admits of a fairly simple interpretation in terms of Benson's restricted rotor theory. On physical grounds, the exponential law appears more reasonable than the power law.
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    International Journal of Chemical Kinetics 13 (1981), S. 323-323 
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    Keywords: Chemistry ; Physical Chemistry
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  • 52
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    International Journal of Chemical Kinetics 13 (1981), S. 333-365 
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Models for the energy profile along the reaction coordinate are utilized to determine the barrier's height and location as a function of ΔG. These form the basis for structure-reactivity correlations and afford a unified formulation for various postulates in the field of physical organic chemistry. Current experimental evidence is examined for the resulting correlations, and some of their applications as an aid to the chemical kineticist are presented.
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    International Journal of Chemical Kinetics 13 (1981), S. 411-416 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The entropy of activation for the hydrolysis of pentaphenoxyphosphorane in 25% aqueous dioxane is -188 J/mol deg. The enthalpy of activation is 22.5 kJ/mol, which is small for the relatively slow reaction. This suggests that the reaction is a multistep process having a preliminary equilibrium with a negative heat of reaction. This conclusion is supported by the results obtained for the hydrolysis of C6H5[OCH(CF3)2]2. A kinetic isotope effect kH2O/kD2O of 3.46 was found for the latter reaction. Orders in water were obtained, and a mechanism of hydrolysis is proposed.
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    International Journal of Chemical Kinetics 13 (1981), S. 497-501 
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A competitive reaction study for two isoelectronic peroxides (peroxodisulfate S2O82- and peroxodiphosphate P2O84-) interacting with the free radical ·Clpar;CH3)2OH is described. The radical formation is initiated by photolysis, the amounts of peroxide remaining analyzed volumetrically. It is found that persulfate reacts with the organic radical over 100 times more rapidly than does perphosphate. Mechanistic consequences in relation to previous work are briefly discussed.
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  • 55
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    International Journal of Chemical Kinetics 13 (1981), S. 527-541 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The decay of photochemically generated tert-butyl radicals in methylcyclopentane solutions containing chloroform is studied by time-resolved ESR spectroscopy. In the pure solvent it perfectly follows the second-order rate law for radical self-termination. Increasing chloroform concentrations cause increasing admixture of a pseudo-first-order decay from which the rate constant of the title reaction is obtained. For 273 K ≦ T ≦ 323 K, \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}\,{\rm k(}M^{{\rm - 1}}\sec ^{ - 1}) = (8.41 \pm 0.14) - \frac{{8.12 \pm 0.18}}{\theta } $$\end{document} where θ = 2.303RT kcal/mol. CIDNP studies of the reaction mechanism and NMR product yields show H and Cl abstractions to occur with the temperature-independent ratio kH/kCl = 1.4 ± 0.1. The results point to polar effects in the transfer reactions of tert-butyl. The potential of time-resolved ESR spectroscopy in studies of first- and pseudo-first-order reaction rates is discussed.
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  • 56
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    International Journal of Chemical Kinetics 13 (1981) 
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 57
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    International Journal of Chemical Kinetics 13 (1981), S. 615-625 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The decomposition of cyclobutyl chloride following multiple infraredphoton excitation has been investigated. The primary photolysis products are butadiene, from elimination of HCl, and ethylene and vinyl chloride, fromring scission. The vinyl chloride undergoes secondary decomposition to acetylene and HCl. In addition to these products, known from thermal VLPP experiments, we also find 1-butene, which may arise from a higher energy C—Cl homolysis channel. Collisions with either reactant molecules oradded buffer gas lead to cooling of the laser-produced vibrational energy distributions. The average amount of energy removed per collision is 15-20 kcal/mol for self-collisions and 2-4 kcal/mol with argon.
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    International Journal of Chemical Kinetics 13 (1981), S. 667-675 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The absolute rate constant for the reaction of methyl radicals with ozone has been measured as a function of temperature. Small concentrations of CH3 were generated by flash photolyzing CH3NO2 at 193 nm with an ArF laser. A photoionization mass spectrometer was used to follow the rate of decay of CH3 at various ozone concentrations. The resulting rate constants could be fit by the expressions \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = (5.4 \pm 1.5) \times 10^{ - 12} \exp [(- 216 \pm 80)/T]{\rm cm}^3 /{\rm molec}\,{\rm s} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = (2.6 \pm 0.7) \times 10^{ - 12} {\rm (T/300)}^{{\rm 0}{\rm .71} \pm {\rm 0}{\rm .34}} {\rm cm}^3 /{\rm molec}\,{\rm s} $$\end{document} over the temperature range of 243-384 K. These rate constants can be modeled by simple transition state theory using reasonable parameters for the activated complex. Use of this rate constant shows that less than 1% of the methyl radicals formed in the stratosphere react with ozone.
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  • 59
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    International Journal of Chemical Kinetics 13 (1981), S. 693-693 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    International Journal of Chemical Kinetics 13 (1981), S. 707-728 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction C2H5 + O2 → C2H5O2 in glassy methanol-d4 and the H-atom abstraction by CH3, C2H5, and n-C4H9 radicals in C2H5OH + C2D5OH and CD3CH2OH + C2D5OH glassy mixtures have been studied by electron spin resonance. The analysis of the dependence of the reaction rates on the concentration of O2 (oxidation) and C2H5OH, CD3CH2OH (H-atom abstraction) has shown that the √t law is not conditioned by the existence of regions characterized by different rate constants.
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  • 61
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    International Journal of Chemical Kinetics 13 (1981) 
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    Keywords: Chemistry ; Physical Chemistry
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  • 62
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    International Journal of Chemical Kinetics 13 (1981), S. 799-815 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: H atoms react with C2H5SSC2H5 to give C2H5SH as the sole retrievable product with φ = 2.32 at 25°C and 2.84 at 145°C. The primary reaction is postulated to be H + C2H5SSC2H5 ← C2H5SH + C2H5S with k1 = (4.73 ± 0.64) × 1013 exp [-(1710 ± 69)/RT] cm3/mol·s relative to the rate constant of the H + C2H4 ← C2H5 reaction. The high value of the entropy of activation suggests the presence of partial hydrogen bonding in diethyldisulfide which is broken in the transition state.Ethylmethyldisulfide reacts similarly: H + C2H5SSCH3 ← C2H5SH + CH3S or CH3SH + C2H5S. The thiyl radicals propagate a chain of radical exchange reactions forming the symmetrical disulfides with exposure-time-dependent quantum yields. The overall kinetics conform to a 16-step mechanism from which the rate constants of the elementary reactions could be established by computer modeling. Thiyl radicals react considerably more slowly with disulfides than H atoms.
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    International Journal of Chemical Kinetics 13 (1981), S. 873-881 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CFBr radicals produced by the reaction of atomic oxygen with F2CCFBr were monitored in a discharge flow system by fluorescence excited at 424 nm. The rate coefficients for reactions of the CFBr radicals were measured between 298 and 358 K, and the following values were obtained in units of cm3/molec·s: O2 〈 2 × 10-16 at 353 K; NO 〈 10-14 at 298 K; F2CCFBr 〈 10-15 at 298 K; Cl2 (1.9 ± 0.6) × 10-12 exp(-762 ± 92/T) Br2 (1.4 ± 0.3) × 10-12 exp(-533 ± 62/T).
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    International Journal of Chemical Kinetics 13 (1981), S. 865-872 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Consideration of current information on the dependence of the electron transfer rate on the radial separation distance and on the reactants′ radial distribution function suggests for adiabatic transfers a frequency factor closer to 1012M-1 s-1 than to 1011M-1 s-1. One effect is to raise the λ values estimated from self-exchange rate constants, and to extend thereby the range of ΔG°'s in which the “inverted region′” is masked by a diffusion-controlled reaction rate.
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    International Journal of Chemical Kinetics 7 (1975), S. 23-31 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The high-temperature oxidation of formaldehyde in the presence of carbon monoxide was investigated to determine the rate constant of the reaction HO2 + CO = CO2 + OH (10). In the temperature range of 878-952°K from the initial parts of the kinetic curves of the HO2 radicals and CO2 accumulation at small extents of the reaction, when the quantity of the reacted formaldehyde does not exceed 10%, it was determined that the rate constant k10 is \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{10} = (1.7 \pm 0.5) \times 10^{ - 10} \exp [ - (23,000 \pm 3000/RT)]\,{\rm cm}^{\rm 3} /{\rm molec}{\rm.sec} $$\end{document} A computer program was used to solve the system of differential equations which correspond to the high-temperature oxidation of formaldehyde in the presence of carbon monoxide. The computation confirmed the experimental results. Also discussed are existing experimental data related to the reaction of HO2 with CO.
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    Keywords: Chemistry ; Physical Chemistry
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    Topics: Chemistry and Pharmacology
    Notes: Modified nuclear recoil techniques have been used to obtain accurate relative bimolecular rate coefficients for thermally induced hydrogen abstraction reactions by atomic fluorine. New results are reported for 12 hydrocarbons and partially fluorinated hydrocarbons studied at 303°K.
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    International Journal of Chemical Kinetics 7 (1975), S. 45-62 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism of the electronically excited sulfur-dioxide sensitized isomerization of cis-2-butene has been studied through the measurement of the initial quantum yields of trans-2-butene formation in 3130-A irradiated gaseous binary mixtures of SO2 and cis-2-butene and ternary mixtures of SO2, cis-2-butene, and CO2. The kinetic treatment of the present data from the SO2—C4H8 mixtures and those of recent similar studies of Penzhorn and Güsten [3] and Cox [4] are all consistent with the involvement of only the long-lived fluorescent 1B1 and phosphorescent 3B1 states of SO2 in the isomerization mechanism. The data give (k2a + k2b)=0.21±0.04; SO2(1B1) + SO2 → SO2(3B1) + SO2(2a); SO2(1B1) + SO2 → (2SO2) (2b). The analogous intersystem crossing ratio for the SO2(1B1)-cis-2-butene quenching collisions is the largest observed among the many quencher molecules studied; the value lies in the range of 0.85 to 0.37, with the extremes representing different choices of alternative data and possible mechanisms. From the present data the ratio of the SO2(3B1) quenching rate constant with SO2 to that with cis-2-butene as quencher is estimated to be (2.7±1.2) × 10-3, in good agreement with our directly measured ratio from lifetime studies (2.91±0.23) × 10-3 [30-32], and the value found in isomerization studies by Cox (2.40±0.09) × 10-3 [4]. The simple two-excited state mechanism, which is seemingly applicable to the relatively low-pressure binary SO2-butene mixture results, is not adequate to explain the data obtained in experiments with large quantities of added CO2 gas. Here an “excess” quantum yield of isomerization is observed. Several alternative mechanisms can be used to rationalize these results, but all alternatives must incorporate some other excited SO2 species (X) as well as SO2(3B1) and SO2(1B1). The kinetics suggest that the ill-defined state is unreactive toward the olefin and decays nonradiatively to SO2 largely in experiments at the lower pressures, X → SO2 (11); it may generate SO2(3B1) in a collisionally induced process at high added inert gas (CO2) pressures, X + CO2 → SO2(3B1) + CO2 (10a) and X + CO2 → SO2 + CO2 (10b). The data give k11/(k10a + k10b)=0.026 mole/l.
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    International Journal of Chemical Kinetics 7 (1975), S. 143-157 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the reactions of O(3P) and D atoms with cyclohexane have been investigated using fast-flow techniques. The rates of reaction were computed by monitoring changes in both atom and cyclohexane concentrations using electron spin resonance and mass spectrometric methods, respectively. The O(3P) + C6H12 reaction was studied over a temperature range of 344 to 513°K and we obtain a specific rate constant of (3.2±0.6) × 1014 exp (-4400±400/RT) cm3/mole·sec for this reaction. The only reaction product detectable mass spectrometrically under flow conditions of excess oxygen atoms is formaldehyde.The D + C6H12 reaction was studied over a temperature range of 297 to 596°K. A specific rate constant of (4.1±1.0) × 1013 exp (-4000±300/RT) cm3/mole·sec was obtained for this reaction. On the basis of the results obtained in these studies, the important primary process in both the O(3P) and D atom reactions is concluded to be abstraction of a hydrogen atom from the cyclohexane molecule.
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    International Journal of Chemical Kinetics 7 (1975), S. 161-182 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quantum yields of SO3 formation have been determined in pure SO2 and in SO2 mixtures with NO, CO2, and O2 using both flow and static systems. In separate series of experiments excitation of SO2 was effected within the forbidden band, SO2(3B1) ← \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm SO}_2 (\tilde X,^1 A_1 ) $$\end{document}, and within the first allowed singlet band at 3130 Å. The values of ΦSO3 were found to be sensitive to the flow rate of the reactants. These results and the apparently divergent quantum yield results of Cox [10], Allen and coworkers [24, 26, 29], and Okuda and coworkers [11] were rationalized quantitatively in terms of the significant occurrence of the reactions SO + SO3 → 2SO2 (2), and 2SO → SO2 + S [or (SO)2] (3), in experiments of long residence time. From the present rate data, values of the rate constants were estimated, k2=(1.2±0.7) × 106; k3=(5±4) × 105 l·/mole · sec. ΦSO3 values from triplet excitation experiments at high flow rates of NO—SO2 and CO2—SO2 mixtures showed the sole reactant with SO2 leading to SO3 formation in this system to be SO2(3B1); SO2(3B1) + SO2 → SO3 + SO(3Σ-) (la); k1a=(4.2±0.4) × 107 l./mole · sec. With excitation of SO2 at 3130 Å both singlet and triplet excited states play a role in SO3 formation. If the reactive singlet state is 1B1, the long-lived fluorescent state, SO2(1B1) + SO2 → SO3 + SO (1 Δ or 3Σ-) (lb), then k1b=(2.2±0.5) × 109 l./mole · sec. From the observed inhibition of SO3- formation by added nitric oxide, it was found that the SO3-forming triplet state, generated in this singlet excited SO2 system, had a relative reactivity toward SO2 and NO which was equal within the experimental error to that observed here for the SO2(3B1) species. Either SO2(3B1) molecules were created with an unexpectedly high efficiency in 3130 Å excited SO2(1B1) quenching collisions, or another reactive triplet (presumably 3A2 or 3B2) of almost identical reactivity to SO2(3B1) was important here.
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    International Journal of Chemical Kinetics 7 (1975), S. 273-285 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the thermal bromination reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Br + CF}_{\rm 3} {\rm I} \to {\rm IBr + CF}_{\rm 3} {\rm Br} $$\end{document} have been studied in the range of 173-321°C. For the step we obtain \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}\,k_{11} \,({\rm cm}^{\rm 3} /{\rm mole} \cdot {\rm sec) = (13}{\rm .19) - (10840} \pm {\rm 460)/}\theta $$\end{document} where θ=2.303RT cal/mole. From the activation energy for reaction (11), we calculate that \documentclass{article}\pagestyle{empty}\begin{document}$$ D({\rm CF}_{{\rm 3}^{\rm - } } {\rm I) = 52}{\rm .6} \pm {\rm 1}{\rm .1}\,{\rm kcal/mole}\,{\rm at 25}{}^{\rm 0}{\rm C} $$\end{document} This is compared with previously published values of D(CF3-I). The relevance of the result to published work on kc for a combination of CF3 radicals is discussed.
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    International Journal of Chemical Kinetics 7 (1975), S. 331-339 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate of the inhibited pyrolysis of pentachloroethane was studiedover the temperature range of 820 to 865°K using the toluene-carrier technique in a stirred-flow reactor. The pyrolysis rate was found to be first order in reactant, and the rate constant is described by k=1011.6±0.7 exp [(-48,200±2600)/RT] sec-1. An increase by a factor of 6.6 in the surface/volume of the reactor had a negligible effect on the rate. This observation, in addition to a reevaluation of earlier kinetic data for the pyrolysis of pentachloroethane, lead to the following conclusions concerning the pyrolysis mechanism. The initiation and termination as well as the propagation reactions were homogeneous, the termination involved both Cl and C2Cl5 radicals (crosstermination), and autocatalysis was caused by interaction between chlorine and pentachloroethane rather than by dissociation of molecular chlorine.
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    International Journal of Chemical Kinetics 7 (1975), S. 399-415 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of CFClCFCl and CF2CCl2 were studied at room temperature by chlorine- and oxygen-atom initiation. The chlorine-atom initiated oxidation of CFClCFCl yields CCl2FCF(O) as the exclusive product. Its quantum yield is ∼420, which gives k3a/k3b=210 where reactions (3a) and (3b) are The O(3P)—CFClCFCl reaction gives CClFO with a quantum yield of 0.80, polymer, and small amounts of an unidentified product which is probably cyclo-(CFCl)3. Thereaction paths are with k9a/k9=0.80. The overall reaction of O(3P) with CFClCFCl proceed one fifth as fast as the O(3P)-C2F4 reaction. When O2 is also present, the same free-radical chain oxidation occurs by O(3P)initiation as by chlorine-atom initiation.The chlorine-atom initiated oxidation of CF2CCl2 gives CF2ClCCl(O) as the major product, with quantum yields ranging from 42 to 85. Smaller amounts of CF2O and CCl2O are produced in equal amounts with quantum yields of ∼3.5. The reactions responsible for the products are The O(3P)-CF2CCl2interaction yields CF2O and with quantum yields of 1.0 and ∼0.85, respectively. In thepresence of O2 the radical chain products are observed, but the mechanism is different than that for other chloroolefins.
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    International Journal of Chemical Kinetics 7 (1975), S. 639-648 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants for the combination of methyl radicals with NO and O2 have been measured by flash photolysis of azomethane coupled with product analysis by gas chromatography. Values of the rate constants have been obtained over the pressure region from 50 to 700 torr with He, N2, and Ar as quenching molecules.The high-pressure limits were obtained through an RRKM model calculation and were found to be \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {{\rm CH}_{\rm 3} + {\rm NO} + {\rm M} \to {\rm CH}_{\rm 3} {\rm NO} + {\rm M}} \hfill & {k_\infty = 3.2 \times 10^{ - 11} {{{\rm cm}^{\rm 3} } \mathord{\left/ {\vphantom {{{\rm cm}^{\rm 3} } {{\rm molec} \cdot {\rm sec}}}} \right. \kern-\nulldelimiterspace} {{\rm molec} \cdot {\rm sec}}}} \hfill \\ {{\rm CH}_{\rm 3} + {\rm O}_{\rm 2} + {\rm M} \to {\rm CH}_{\rm 3} {\rm O}_{\rm 2} + {\rm M}} \hfill & {k_\infty = 1.7 \times 10^{ - 12} {{{\rm cm}^{\rm 3} } \mathord{\left/ {\vphantom {{{\rm cm}^{\rm 3} } {{\rm molec} \cdot {\rm sec}}}} \right. \kern-\nulldelimiterspace} {{\rm molec} \cdot {\rm sec}}}} \hfill \\ \end{array} $$\end{document} The rate constants were measured relative to the methyl combination reaction k1 with k1 = 9.5 × 10-11 cm3/molec · sec. The RRKM model suggests D0(CH3—O2) = 32 ± 3 kcal/mole.
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    International Journal of Chemical Kinetics 7 (1975), S. 907-917 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanism and kinetics of the reaction of O(3P) atoms with propane were investigated using molecular modulation spectroscopy, with the O(3P) atoms being generated by the Hg photosensitized decomposition of N2O. The absorption spectrum of the X2II3/2 state of OH was observed in the ultraviolet between 307 and 309 nm, and it was confirmed that OH was the product of the O(3P) reaction with propane. The rate constants for the reactions of O(3P) and OH with propane were determined to be 3.9±0.7±1010 and 1.19±0.05±1012 cm3/mole·sec, respectively, at T=56±5°C.
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    International Journal of Chemical Kinetics 7 (1975), S. 919-926 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetics of protonation of Li+, Na+, K+, and Cs+ salts of anthracene radical anions (A-·,Cat+) and dianions (A2-, 2Cat+) by MeOH and MeOD in tetrahydrofuran (THF) and dimethoxyethane (DME) led to the determination of the isotope effect (kH/kD) in the following reactions: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm MeOH(MeOD) + A}\bar \cdot {\rm,Cat}^{\rm + } \to MeO^ - {\rm,Cat}^{\rm + } {\rm + AH} \cdot {\rm (D)} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm (MeOH)}_{\rm 2} {\rm or (MeOD)}_{\rm 2} {\rm + A}\bar \cdot {\rm,Cat}^{\rm + } \to {\rm MeOH,MeO}^ - {\rm,Cat}^{\rm + } {\rm + AH} \cdot {\rm (D)} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm MeOH (MeOD) + A}^{{\rm 2 - }} {\rm,2Cat}^{\rm + } \to {\rm MeO}^ - {\rm,Cat}^{\rm + } {\rm + AH(D)}^{{\rm - 1}},{\rm Cat}^{\rm +} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm MeOH (MeOD) + (A,Cat}^{\rm + } {\rm,A}^{{\rm 2 - }} {\rm,Cat}^{\rm + }) \to {\rm MeO}^ - {\rm,Cat}^{\rm + } {\rm + A + AH(D)}^{\rm - },{\rm Cat}^{\rm +} $$\end{document}Studies of cation and solvent influence on the rate constants of these reactions and on the magnitude of the isotope effect permitted us to draw some conclusions about the structure of the pertinent transition states. It seems that only the tight A-·,Na+ pairs participate in the protonation, and on this basis the fraction of tight ion paris of A-·,Na+ in DME was estimated. Our results have been compared with data reported in the literature.
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    International Journal of Chemical Kinetics 13 (1981) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    International Journal of Chemical Kinetics 13 (1981), S. 125-133 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method of theoretical prediction of the kinetic rate constants of fast chemical reactions in solutions is presented. It takes into account the effect of finite diffusive displacements of the reacting molecules. The approach is based on the solution of the steady-state Fokker-Planck equation by the moments method of Grad developed in the theory of coagulation of aerosol particles. A comparison of the predicted rate constants with the experimental data provided by Schuh and Fischer for the self-reaction of tert-butyl radicals in n-alkanes shows a good correspondence.
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  • 78
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    International Journal of Chemical Kinetics 13 (1981), S. 317-320 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    International Journal of Chemical Kinetics 13 (1981), S. 303-316 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate of the reverse reaction of the system has been measured in the range of 584-604 K from a study of the azomethane sensitized pyrolysis of isobutane. Assuming the published value for the rate constant of recombination of t-butyl we obtain \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_{{\rm - 1}} (\sec ^{- 1}) = 14.67 - 39.4\,{\rm kcal}/{\rm mol}/(2.3{\rm RT}) $$\end{document} Combination with our published data for k1 permits the evaluation \documentclass{article}\pagestyle{empty}\begin{document}$$ \log K_1 ({\rm atm}^{ - 1}) = 7.94\,\,{\rm at}\,\,600{\rm K} $$\end{document}We have modified a previously published structural model of t-butyl by the inclusion of a barrier to free rotation of the methyl groups in order to calculate values of the entropy and enthalpy of t-butyl as a function of temperature. Using standard data for H and for i-C4H8 we obtain \documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta H_ f^\circ(t - {\rm butyl},\,300\,{\rm K})({\rm kcal}/{\rm mol}) = 10.6 \pm 0.5 $$\end{document}We have obtained other, independent values of this quantity by a reworking of published data using our new calculations of the entropy and enthalpy of t-butyl. There is substantial agreement between the different values with one exception, namely, that derived from published data on the equilibrium \documentclass{article}\pagestyle{empty}\begin{document}$$ i - {\rm C}_{\rm 4} {\rm H}_{{\rm 10}} + {\rm I}\rightleftharpoons t{-} {\rm C}_4 {\rm H}_9 + {\rm HI} $$\end{document} which is significantly lower than the other values.We conclude that the value \documentclass{article}\pagestyle{empty}\begin{document}$$ \Delta H_ f^\circ(t - {\rm butyl},\,300\,{\rm K})({\rm kcal}/{\rm mol}) = 10.5 \pm 1.0 $$\end{document}obtained from the present work and a reworking of published data which involves the use of experimental data on t-butyl recombination is incompatible with the result based on iodination data.
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  • 80
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    International Journal of Chemical Kinetics 13 (1981), S. 403-410 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of pyrolysis of 4-chloro-2-butanone in the gas phase have been determined in a static system seasoned with the products of decomposition of allyl bromide. The reaction is catalyzed by hydrogen chloride. Under maximum catalysis of HCl, the kinetics were found to be of order 1.5 in the substrate suggesting that a complex elimination is involved. The reaction, when maximally inhibited with propene, appears to undergo a unimolecular elimination and follows a first-order law kinetics. The products are methylvinyl ketone and hydrogen chloride. The kinetics have been measured over the temperature range of 402.0-424.4°C.The rate coefficients are given by the Arrhenius equation \documentclass{article}\pagestyle{empty}\begin{document}$ \log k_1 (\sec ^{ - 1}) = (13.67 \pm 0.69) - (225.2 \pm 8.6)\,{\rm kj}/{\rm mol}/2.303RT\angle $\end{document}. Thepyrolysis of 4-chloro-2-butanone is 31 times greater in rate than that of ethyl chloride at 440°C. This large difference in rate may be attributed to the -M effect of the acetyl substituent in the pyrolysis of the former halo compound.
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  • 81
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    International Journal of Chemical Kinetics 13 (1981), S. 7-21 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pyrolysis of gaseous neopentyl bromide to 2-methyl-2-butene, 2-methyl-1-butene, and hydrogen bromide was studied under conditions of maximal inhibition by cyclohexene over the temperature range of 389-444°C. This reaction was shown to beconsistent with a first-order homogeneous molecular process, with Arrhenius parameters of E = 247 ± 5 kJ/mol and log A (sec-1) = 14.2 ± 0.3. Examination of the uninhibited reaction showed it to be a radical process, simpler than that with neopentyl chloride, there being only one propagation step, thedissociation of the γ-radical to 1,1-dimethylcyclopropane and a bromine atom.
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  • 82
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    International Journal of Chemical Kinetics 13 (1981), S. 69-84 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of O(3P) atoms with propanehas been studied at temperatures near 300 K by using a discharge flow system. Oxygen atoms were generated in the absence of molecular oxygen by the reaction N + NO → N2 + O, nitrogen atoms having been generated in a microwave discharge. Rate constants for the reaction were measured in two ways, either by measurement of O-atom decay in the presence of excess propane or by measuring the change in propane concentration after an appropriate time in the presence of an excess of oxygen atoms. The two methods were in good agreement, and the mean rate constant at 306 K is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = (4.7 \pm 0.8) \times 10^6 {\rm dm}^3 /{\rm mol}\;\sec $$\end{document} A study of the products of the reaction under conditions corresponding to complete removal of oxygen atoms has shown that an important product of the reaction in the early stages is propene. This is difficult to explain interms of a mechanism involving alkoxy radicals similar to that which has been proposed for some other O(3P)-hydrocarbon reactions. An alternative mechanism is proposed in terms of successive hydrogen abstraction reactions.
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    International Journal of Chemical Kinetics 13 (1981), S. 119-123 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactivity of amines towards tert-butoxy radicals depends upon the amine ionization potential and the solvent, indicating that polar structures contribute to the reactivity of these compounds. Nevertheless, the dependence with the amine potential is smaller than the one obtained for the quenching of carbonyl excited states by amines and other factors as the strength of the broken hydrogen bond and steric hindrance are also significant in determining the rate of the process.
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    International Journal of Chemical Kinetics 13 (1981), S. 741-753 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study of the thermal decomposition of an acetylene-ethane-d6 mixture indicates that the rate constant for hydrogen abstraction from acetylene by methyl is more than 20 times less than for abstraction from ethane. Isotopic exchange is initiated by a rapid reaction between product D atoms and C2H2. A series of experiments involving the reactions of a D2-acetylene mixture indicated that a molecular exchange process was also occurring, and it was shown that d[C2HD]/dt = k[D2]0.7[C2H2]0.3, effective activation energy = 15.8 kcal/mol. This mechanism made an insignificant contribution to isotope exchange in C2H2-C2D6 mixtures.
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    International Journal of Chemical Kinetics 13 (1981), S. 817-831 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methyl nitrate decomposition is accompanied by self-heating. Using very fine thermocouples, direct measurements of excess temperatures have been made to establish the intensity and extent of self-heating in nonisothermal reaction. The measurements are displayed as contourlines of equal degrees of temperature excess on the pressure-temperature ignition diagram.A twofold kinetic investigation has been made of the overall reaction. One part concentrates on achieving isothermal conditions and full characterization of intermediate products. It uses mass-spectrometric analyses both to establish stoichiometry throughout decomposition and to validate velocity constant measurements derived from continuous pressure-time records. The best value for E = 151 ± 3 kJ/mol is about 10 kJ/mol less than previously.The other part deliberately invades the nonisothermal region to test the qualitative and quantitative predictions of theory (1) that uncorrected reaction orders and activation energies will exceed their isothermal values, (2) that their relative excess (δn/n, δE/E) will be about the same, and (3) that they will be dependent in a simple and predictable way on the reduced excess central temperature.
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    International Journal of Chemical Kinetics 7 (1975), S. 109-123 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A very low-pressure pyrolysis (VLPP) apparatus has been constructed and shown to yield kinetic data consistent with other VLPP systems. The technique has been applied to the pyrolysis of cyclobutyl cyanide over the temperature range of 833-1203°K. The reaction was found to proceed via a single pathway to yield ethylene and vinyl cyanide. If A∞ is based on previous high-pressure data for this reaction and for cyclobutane pyrolysis, then RRKM theory calculations show that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}\,k_\infty ({\rm sec}^{{\rm - 1}}) = 15.0 - (57.0 \pm 1.0)/\theta $$\end{document} where θ=2.303 RT in kcal/mole. If A∞ is adjusted relative to the more recent parameters for cyclobutane pyrolysis suggested by VLPP studies, then the Arrhenius expression becomes \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log }\,k_\infty ({\rm sec}^{{\rm - 1}}) = 15.9 - (59.1 \pm 1.0)/\theta $$\end{document} The cyano group reduces the activation energy for cyclobutane pyrolysis by 6±1 kcal/mole, and on the basis of a biradical mechanism this value may be attributed to the cyano stabilization energy.
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    International Journal of Chemical Kinetics 7 (1975), S. 183-194 
    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 chloromethanes (CM)CCl4, CHCl3, and CH2Cl2 by radiolytically generated cyclohexyl radicals has been studied in the liquid phase by a competitive method. The halogen abstraction data have been 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: TextCMlog A(CM)/A(C2Cl4)E(CM)—E(C2Cl4)(kcal/mole)log A(CM)(1./mole·sec)E(CM) (kcal/mole)Temperaure Range(°K)CCl40.72±0.02-1.42±0.059.40±0.085.88±0.15333-453CHCl30.77±0.062.86±0.019.45±0.1210.16±0.11392-492CH2Cl20.56±0.126.37±0.279.42±0.1813.67 ± 0.37463-543The error limits are the standard deviations from least mean square Arrhenius plots.The possible application of the Evans-Polanyi relationship to chlorine atom abstraction reaction from CM is considered.
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    International Journal of Chemical Kinetics 7 (1975), S. 223-247 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High-temperature (〉1000°K) pyrolysis of acetaldehyde (∼1% in an atmosphere of pure nitrogen) was examined in a turbulent flow reactor which permits accurate determination of the spatial distribution of the stable species. Results show that the products in order of decreasing importance are CO, CH4, H2, C2H6, and C2H4. Rates of formation were consistent with the Rice-Herzfeld mechanism by including reactions to explain C2H4 formation and the possible presence of ketene. A steady-state treatment of the complete mechanism indicates that the overall reaction order decreases from \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{3}{2} $\end{document} to 1, which is supported by the new experimental data. Using earlier low-temperature results, the rate constant for the reaction CH3CHO → CH3 + CHO (1) was found as k1=1015.85±0.21 exp (-81,775±1000/RT) sec-1. Also, data for the ratio of rate constants for reactions CH3CHO + CH3 → CH4 + CH3CO (4) and 2CH3 → C2H6(6) were fitted to the empirical expression k4/k61/2=10-13.89±0.03T6.1 exp(-1720±70/RT) (cm3/mole·sec)1/2 and causes for the curvature are discussed. The noncatalytic effect of oxygen on acetaldehyde pyrolysis at high temperature is explained.
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    International Journal of Chemical Kinetics 13 (1981), S. 785-786 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    International Journal of Chemical Kinetics 13 (1981), S. 787-788 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
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    Topics: Chemistry and Pharmacology
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    International Journal of Chemical Kinetics 13 (1981), S. 833-844 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Arrhenius parameters for the decomposition reactions of various alkoxy radicals are evaluated. The recommended values for tert-butoxy radical decomposition reaction are log A (s-1) = 14.1, Ea = 15.3 kcal/mol. The parameters give reasonably self-consistent results with related rate constants, product distributions of hydrocarbon oxidation reactions, and the values reported in different laboratories in different environments.A reworking of data by Batt et al. on RO + NO and RO + NO2 leads to a lowering of his A factors for these reactions by a factor of 5. It also leads to a similar lowering of the A factors for RO decompositions. The intrinsic activation energies E for the addition of alkyl radicals R to the carbonyl group are not only found to be a function of the exothermicity of reaction, but they are also dependent on the nucleophilicity of the alkyl radicals. For each radical R (Me, Et, i-Pr) the data can be fit to an Evans-Polanyi plot E = a + b (δH), where a uniform slope b = 0.58 can be found for all R. The intercepts a are then found to decrease nearly linearly with the decreasing ionization potential of R, namely, a = 2.1 [IP] - 6.2 (kcal/mol), with the ionization potential given in electron volts.
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    International Journal of Chemical Kinetics 7 (1975), S. 15-22 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas-phase photolysis of perfluoroacetone in the presence of ethane has been shown to result in the production of significant amounts of 1, 1-bis(trifluoromethyl)propanol-1, (CF3)2(C2H5)COH, and 1, 1, 4, 4-tetrakis(trifluoromethyl)butane-1, 4-diol, (CF3)2C(OH)-CH2CH2C(OH)(CF3)2. A mechanism is presented which accounts for the relative rates of formation of these products at room temperature.
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    International Journal of Chemical Kinetics 7 (1975), S. 63-76 
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A kinetic investigation of electronically excited arsenic atoms in the low-lying states, As(4p3 2DJ) and As(4p3 2PJ), ca. 1.33 and 2.28 eV, respectively, above the 44S3/2 ground state, has been carried out by atomic absorption spectroscopy. Atoms in these optically metastable states were generated by the pulsed irradiation of suitable arsenic compounds (AsMe3 for 2D and AsCl3 for 2P) in different spectral regions and monitored photoelectrically by time-resolved attenuation of atomic resonance radiation. Rate constants for the deactivation of these two states are reported for a range of collision partners. The data are compared with those of the analogous states of lighter atoms in group V, namely, P(32DJ, 32PJ) and N(22DJ, 22PJ), and discussed in terms of spin and orbital symmetry considerations.
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    International Journal of Chemical Kinetics 7 (1975), S. 99-107 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photochemistry of azoisopropane is reinvestigated at 366 nm over an extended pressure range by using n-butane as an added bath gas, and over a range of temperature from 277° to 180°C. The Stern-Volmer type plot of the N2 product quantum yield is interpreted in terms of the decomposition of the vibrationally excited upper singlet and triplet states, with the onset of the dissociation of the vibrationally equilibrated triplet state as the temperature is increased. The energy barrier for the dissociation of the vibrationally equilibrated first triplet state is found to be 8.8 kcal/mole. Triplet sensitization experiments with biacetyl correlate with our observations, and it is suggested that the proposed mechanism is generally applicable to the photodissociation of acyclic azoalkanes at 366 nm, based on a comparison of our data with those of Wu and Rice on hexafluoroazomethane.
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    International Journal of Chemical Kinetics 7 (1975) 
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    Keywords: Chemistry ; Physical Chemistry
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    International Journal of Chemical Kinetics 7 (1975), S. 195-203 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The π*←n excited state kinetics of hexafluoroacetone are reinvestigated in the presence of a vibrational relaxer and sufficient triplet state quencher so that only the reactions of the electronically excited upper singlet state are examined. From a Stern-Volmer type analysis it is concluded that vibrational relaxation of the initially formed vibrationally and electronically excited upper singlet state is via a multistage collisional mechanism. An activation energy of about 6 kcal/mole is reported for the unimolecular decomposition of the upper singlet state.
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    International Journal of Chemical Kinetics 7 (1975), S. 215-222 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate equations have been deduced for two possible mechanisms for the reactions of N-methyl-N-nitrosoaniline in acid solution, namely, (1) for the generally accepted intermolecular mechanism which involves denitrosation followed by C-nitrosation and (2) a mechanism involving intramolecular rearrangement which takes place concurrently with denitrosation. The observed rate constants obtained under various experimental conditions are consistent only with mechanism (2). In particular the question of halide ion catalysis differentiates clearly between the two mechanisms. Mechanism (1) predicts a first-order dependence upon chloride (or other halide) ion under all conditions, whereas (2) allows a first-order chloride ion dependence only in the presence of a large excess of a “nitrite trap” such as sulphamic acid, urea, hydrazoic acid, hydroxylamine, etc., whereas at the other limit of high concentration of added N-methylaniline, the rate constants should be independent of the halide ion concentration. The predictions based on mechanism (2) are all borne out by experiment.
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    International Journal of Chemical Kinetics 7 (1975), S. 301-315 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A flow tube method has been used to determine rate constants for the elementary reactions: Oxygen atoms were produced by adding a small excess of NO to a stream of partially dissociated nitrogen, and their reaction with hydrogen halide was monitored by observing the intensity of the NO + O afterglow. Experiments were carried out at temperatures from 293 to 440°K with HCl, and from 267 to 430°K with HBr. The role of secondary reactions was minimised and the residual effects were allowed for. The rate constants for the primary reactions could be matched by Arrhenius expressions: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{1a} = 2.5\left({_ - ^ + } \right.\left. {{}_{0.8}^{1.2} } \right) \times 10^{ - 12} \,{\rm exp}\frac{{{\rm ( - 5}{\rm .9} \pm {\rm 0}{\rm .3}\,{\rm kcal/mole)}}}{{RT}} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{1b} = 4.0( \pm 0.7) \times 10^{ - 12} \,{\rm exp}\frac{{{\rm ( - 2}{\rm .7} \pm {\rm 0}{\rm .1}\,{\rm kcal/mole)}}}{{RT}} $$\end{document} where the units are cm3/molec·sec and the errors correspond to a standard deviation.
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    International Journal of Chemical Kinetics 7 (1975), S. 351-362 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the thermal hydrocracking of indan were investigatedin a high-pressure flow reactor at temperatures from 470 to 530°C, total pressures of up to 300 atm, and molar ratios from 3 to 40. The effect of the hydrogen pressure was reflected especially in a change of the experimental rate equations for the formation of toluene from rT=k [indan]0.5 [hydrogen] to rT=k′ [indan] 0.75[hydrogen]0.75 with hydrogen partial pressureincreasing from 73 to 230 atm. The rate equation of n-propylbenzene remained constant at rPr=k″ [indan] [hydrogen]1.5. Simultaneously the Arrheniusparameters of toluene changed significantly, while those of n-propylbenzene remained unchanged.The observed effect of the hydrogen pressure is explained as a change inthe rates of the intermediate reactions; it provides an excellent agreementbetween the theoretical and experimental data. It was found that the steady-state concentration of the hydrogen atoms, which act as chain carriers in the thermal hydrocracking, was much smaller than the thermodynamic equilibrium concentrations
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    International Journal of Chemical Kinetics 7 (1975), S. 417-432 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A detailed chemical mechanism for the cerium catalyzed bromination and oxidation of malonic acid by bromate has been developed, and complete numerical solutions have been obtained for the temporal behavior of the concentrations of the intermediate species. The many points of similarity with the experimentally observed initial decay, long quiescence, and abrupt transition to sustained oscillation establish confidence in the essential validity of the proposed mechanism. Close examination of the time dependence of these species concentrations as well as the magnitude of the several reaction channels permits the clarification of the switching mechanism causing theoscillatory behavior of this system. The results appear to exhibit limit cycle behavior, in accordance with theoretical predictions.
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