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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 327-349 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Observations are reported of the effect of the buffer gases He, Ne, and CF4, in the pressure range of 0-30 torr, on the branching ratio [HCl]/[DCl] of the unimolecular decomposition The ratio R = kH/kD has been measured in high-pressure thermal decomposition (670-1100 K) and was shown to give a unique measure of the internal energy of the decomposing molecules and hence, with RRKM theory and pressure fall-off data, a time scale for their decomposition.Applying the thermal data to the photolysis leads to the conclusion that excitation and decomposition are produced by the laser spike (high intensity, 70 ns FWHM) and also at a slower rate by the larger, less intense tail (1.6 μs). Added buffer gases quench the latter, leaving the former which, from measurements of R, is shown to correspond to excitations of 115 ± 15 kcal/mol and lifetimes of ∼30 ps. No bond breaking is seen despite the high energies, in accord with theoretical expectations. The results require an enhanced rate of photon absorption by the highly excited molecules, which are about hundredfold greater than that observed for 300 K molecules. Data are also reported for C2H2F2 and the secondary multiphoton photolysis of the ethylenes produced. Effects of beam geometry and wavelength are explored.
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  • 2
    Electronic Resource
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 371-379 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constant for the reaction of ground-state oxygen atoms with methanol has been determined between 297 and 544 K by a phase-shift technique using mercury photosensitized decomposition of N2O to generate oxygen atoms. The relative oxygen atom concentration was monitored by the chemiluminescence from the reaction of oxygen atoms with nitric oxide. The results are accommodated by the Arrhenius expression k1 = (9.79 ± 2.71) × 1012 exp[(-2267 ± 111)/T]cm3/mol·s, where the indicated uncertainties are 95% confidence limits for 10 degrees of freedom. As an incidental part of this work, the third-body efficiency of CH3OH relative to N2O for the reaction O + NO + M → NO2 + M (M = CH3OH) was determined to be 3.1 at 298 K.
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  • 3
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 435-438 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 4
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 417-434 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The flash photolysis resonance fluorescence technique was used to measure the rate constants of the reaction O + O2 + M → O3 + M (M = N2, O2, Ar, and He) as a function of temperature. The results for the rate constants are given by The activation energies with N2, O2, and Ar as third bodies are equal within the experimental error, (-1370 → 340 cal/mol), and the relative third-body efficiencies at 298 K for N2, O2, Ar, and He are 1.00, 0.99, 0.69, and 0.60, respectively.
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  • 5
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 439-445 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 6
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 447-450 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 7
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 647-657 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the gas-phase thermal reaction between CF2(OF)2 and CO has been studied in a static system at temperatures ranging between 110 and 140°C. The only reaction products were CF2O and CO2, giving the following stoichiometry: \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CF}_{\rm 2} {\rm (OF)}_{\rm 2} {\rm + 2CO = 2CF}_{\rm 2} {\rm O + CO}_{\rm 2} {\rm}\Delta n{\rm = 0}$$\end{document} The reaction is homogeneous. The rate is strictly second order in CF2(OF)2 and CO, and is not affected by the total pressure or by the presence of reaction products. Oxygen promotes a sensitized oxidation of CO and inhibits the formation of CF2O.The experimental results in the absence of oxygen can be explained by a chain mechanism similar to that proposed for the reaction between F2O and CO with an overall rate constant of \documentclass{article}\pagestyle{empty}\begin{document}$$k_1 = 1.45 \times 10^9 {\rm exp}(- 20,900/RT)L/mol \cdot s$$\end{document} From the experimental data obtained on the oxygen-inhibited reaction, the rate constant for the primary process can be calculated: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{*{20}c} {({\rm I})} \quad {{\rm CF}_{\rm 2} ({\rm OF)}_{\rm 2} + {\rm CO} \to {\rm CF}_{\rm 2} (\mathop {\rm O}\limits^{\rm .}){\rm OF} + {\rm F}\mathop {\rm C}\limits^{\rm .} {\rm O}} \quad\quad {k_1 = 1.45 \times 10^9 {\rm exp}(- 20,900/RT)L/mol \cdot s} \\\end{array}$$\end{document} The chain length v = 2.5 is independent of the temperature. Taking for collision diameters σCF2(OF)2 = 6 Å and σCO = 3.74 Å, a value α = 5.3 × 10-3 for the steric factor is obtained.
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  • 8
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 669-677 
    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 490-573 K. Initial reactant pressures were varied in the range of 0.2-5.2 torr (I2) and 2-20 torr (C6H5SiH3). The rate of iodine consumption, monitored spectrophotometrically, was found to obey \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm I}_{\rm 2}]}}{{dt}} = \frac{{k_{3/2} [{\rm I}_{\rm 2}]^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} [{\rm C}_{\rm 6} {\rm H}_{\rm 5} {\rm SiH}_{\rm 3}]}}{{1 + k'[HI]/[I_2]}}$$\end{document} both by initial rate and integrated equation fitting procedures. The effect of added initial HI conformed to this expression. The data are consistent with a conventional I-atom propagated chain reaction, and for the step \documentclass{article}\pagestyle{empty}\begin{document}$${\rm I}^{\rm .} + {\rm C}_{\rm 6} {\rm H}_{\rm 5} {\rm SiH}_{\rm 3} \to {\rm C}_{\rm 6} {\rm H}_{\rm 5} \mathop {\rm S}\limits^{\rm .} {\rm iH}_{\rm 2} + {\rm HI}$$\end{document} the rate constant is given by \documentclass{article}\pagestyle{empty}\begin{document}$${\rm log}k_1 (dm^3 /mol \cdot s) = (11.52 \pm 0.08) - (76.8 \pm 0.8{\rm kJ/mol})/RT{\rm ln}10$$\end{document} From this is derived the bond dissociation energy value C6H5SiH2—H = 374 kJ/mol(88 kcal/mol). A comparison with other Si—H dissociation energy values indicates that the “silabenzyl” stabilization energy is small, ≈7 kJ/mol.
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  • 9
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 699-710 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Diethylhydroxylamine, (C2H5)2NOH, was oxidized by NO2 at 25°C in a long-path-length infrared gas cell. The measured products of the reaction were HONO and CH3CHO. The reaction scheme which explains the reaction is was oxidized by NO2, and the reaction was found to be very rapid with k1 〉 10-16 cm3/s. The products of the reaction were verified by both infrared absorption (CH3CHO, C2H5NO) and gas chromatography (CH3CHO, NO).
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  • 10
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 789-799 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of oxidation of phenylthioacetic acid (PTAA) and several substituted phenylthioacetic acids by potassium peroxodiphosphate (PP) in 50% (v/v) aqueous acetic acid have been studied in detail. The rate of oxidation is expressed as \documentclass{article}\pagestyle{empty}\begin{document}$$\frac{{- d[{\rm PP]}}}{{{\rm dt}}} = k[{\rm PP][PTAA][H}^{\rm +}]$$\end{document}An analysis of the dependence of the rate on [H+] reveals that H3P2O8- is the active oxidizing species in the oxidation. The effect of ring substituents on the rate gives a ρ+ value of -0.45 ± 0.03 (r = 0.998, s = 0.02 at 40°C), pointing to the development of an electron-deficient center in the transition state. The results are discussed in terms of a mechanism involving the rate-determining formation of an intermediate between PP and phenylthioacetic acids, followed by the decomposition of the intermediate. These kinetic results are compared with those obtained in the oxidation of phenylthioacetic acids by peroxodisulfate.
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  • 11
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 801-811 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A kinetic study on the oxidation of V(IV) by chloramine-T (CAT) at pH 6.85 by N-bromo succinimide (NBS) in aqueous acetic acid-perchloric acid media and by N-iodo succinimide (NIS) in aqueous perchloric acid medium has been carried out. In all the systems studied the order with respect to the oxidant is unity. NBS and CAT oxidation reactions exhibited Michaelis-Menten type kinetics, and the NIS study indicated unit dependence on [substrate]. Independence on acidity has been observed in the case of CAT and NBS reactions, but NIS reactions exhibited inverse unit dependence on [acid]. Novel solvent influences have been noticed in the case of CAT reactions, but with NIS and NBS reactions retardation in the rate has been observed with an increase in the percentage of acetic acid. Plausible mechanisms consistent with the results have been postulated, and suitable rate laws in consonance with the postulated mechanisms have been derived.
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  • 12
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 813-814 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 13
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 14
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    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 14 (1982), S. 815-821 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The experimental behavior of the cerium- and manganese-catalyzed Belousov Zhabotinskii oscillating reaction with ethyl acetoacetate as organic substrate has been investigated. Under certain conditions the system displays two types of temporal oscillations. Damped highfrequency oscillations appear immediately after the addition of potassium bromate solution to complete the reaction mixture. These high-frequency oscillations may be regarded as being superimposed on an induction period of the type found in the reaction using malonic acid. After the induction period, low-frequency oscillations of the normal type are obtained. Both the high-frequency and the low-frequency oscillations can be monitored with a platinum redox or with a bromide specific ion electrode.
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  • 15
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    International Journal of Chemical Kinetics 14 (1982), S. 839-847 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Relative rate constants for the reaction of OH radicals with a series of ketones have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of hydroxyl radicals. Using a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10-12 cm3 molecule-1 s-1, the rate constants obtained are (× 1012 cm3 molecule-1 s-1): 2-pentanone, 4.74 ± 0.14; 3-pentanone, 1.85 ± 0.34; 2-hexanone, 9.16 ± 0.61; 3-hexanone, 6.96 ± 0.29; 2,4-dimethyl-3-pentanone, 5.43 ± 0.41; 4-methyl-2-pentanone, 14.5 ± 0.7; and 2,6-dimethyl-4-heptanone, 27.7 ± 1.5. These rate constants indicate that while the carbonyl group decreases the reactivity of C—H bonds in the α position toward reaction with the OH radical, it enhances the reactivity in the β position.
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  • 16
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A kinetic spectrophotometric investigation of the reaction of the hydrogen peroxide anion with methyl p-nitrophenyl sulfate in methanol solvent resulted in the evaluation of the pKa of HOOH in methanol at 25°C as 15.8 ± 0.2. Since normal kinetic procedures for the determination of the equilibrium constant K for the process CH3O- + H2O2 ⇄ CH3OH + HO2- were found to be associated with high uncertainty, another procedure was devised to establish the magnitude of K. This method is based on an analysis of the changing slopes of plots of pseudo-first-order rate constants against the total base concentration as the stoichiometric amount of hydrogen peroxide is varied. The method is applicable to any system in which anionic nucleophiles generated in situ compete with solvent anions. Such a corroboration of kinetically determined equilibrium constants is believed essential. The kinetic data allow the specific rate constant kHOO-for the reaction of methyl p-nitrophenyl sulfate with hydrogen peroxide anions to be evaluated and yield the rate constant ratio kHOO-/kMeO- = 8.8 ± 2.2. This confirms the existence of an α effect at saturated carbon in this system.
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  • 17
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    International Journal of Chemical Kinetics 14 (1982), S. 849-859 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate law for the demetallation of the title indium(III)-porphin complex in aqueous acidic thiocyanate media at 3.00M ionic strength was found to be of the form \documentclass{article}\pagestyle{empty}\begin{document}$$+ \frac{{d{\rm [H}_{\rm 4} {\rm P}^{{\rm 2} - } {\rm]}}}{{dt}} = \frac{{ab[{\rm H}^{\rm + }]^2 [{\rm NCS}^ -]^2 }}{{1 + b[{\rm H}^{\rm + }]^2 }}[{\rm InP]}_{\rm t}$$\end{document} where [H4P2-] is the concentration of the diacid product formed, [InP]t is the total concentration of all forms of indium(III)-porphin complex present, and a and b are constants. The constant a is a pseudo-third-order rate constant with the value (0.057 ± 0.005)M-2 s-1 and b has the value 0.704M-2 at 50.5°C. If the mechanism for demetallation involves ringpuckering with the attachment of two H+ ions, then 1/b can be identified with the product K1K2 for the stepwise dissociation of two protons from two ring pyrrolic nitrogen atoms of H2InP-. In the sulfonated tetraphenylporphin used for these studies the ring pyrrolic nitrogen atoms seem to be the most probable sites for protonation. If this identification is correct, the value of 1.42 ± 0.13 found for the product K1K2 shows the enormous effect that the presence of the In3+ center has on the ionization constants of these two protons. That the kinetic studies show saturation effects with respect to proton addition to InP3- may result from the fact that In3+ sits about 0.6 Å above the porphin ring.
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  • 18
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    International Journal of Chemical Kinetics 14 (1982), S. 893-902 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of cleavage of 3-hydroxybicyclo[4.2.0]octa-1,3,5-trien-7-ones in aqueous sodium hydroxide, and of the alkoxy and acetoxy analogues in methanolic sodium methoxide solution, were examined under pseudo-first-order reaction conditions. The dependence of the rate upon the basicity of the solvent, whether measured by H- or by [OR-], reflects the possible structure of the transition state. The deduced mechanism is also supported by the effects of substituents upon the reaction rate. The relative amounts of the volatile reaction products derived from o-toluic acid and from phenylacetic acid are understood in terms of the substituent effect upon the relative stabilities of the carbanions.
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  • 19
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    International Journal of Chemical Kinetics 14 (1982), S. 875-891 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The isomerization reaction of cholest-5-en-3-one has been studied in a solution of cyclohexane using trichloroacetic acid as catalyst. At the same time a general reaction scheme is proposed to be valid for all the cases assayed in which the monomer form of the acid is considered as the only effective catalyst. The experimental results agree with these hypotheses and with the calculation of the individual rate constant together with the reaction order with respect to the catalyst. Semiquantitative studies have been carried out with other catalysts and solvents, confirming the validity of the reaction scheme. The thermodynamic activation parameters have also been calculated, and a comparative study was made with the results of the evaluation of the reaction when it takes place in amphiprotic solvents. A reaction mechanism is proposed based on all the kinetic information obtained.
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  • 20
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    International Journal of Chemical Kinetics 14 (1982), S. 903-917 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetics of the basic hydrolysis of 1-glyceryl mononitrate (1-MNG) and 2-glyceryl mononitrate (2-MNG) were investigated in CO2-free aqueous calcium hydroxide solutions. The hydrolysis reactions were carried out in a temperature-controlled reactor vessel with provision for continuous N2 sparging of the reaction mixture. Both glyceryl nitrate esters hydrolyzed via second-order reaction at 25°C. 2-MNG in calcium hydroxide solution isomerized to 1-MNG, which subsequently hydrolyzed to form NO3-. In strongly basic aqueous solutions of NaOH (30%), 2-MNG is converted to glycidol and NO3-.
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  • 21
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    International Journal of Chemical Kinetics 14 (1982), S. 919-926 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Relative rate constants for the gas-phase reactions of OH radicals with a series of alkyl nitrates have been determined at 299 ± 2 K, using methyl nitrite photolysis in air as a source of OH radicals. Using a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10-12 cm3/molec·s, the rate constants obtained are (× 1012 cm3/molec·s): 2-propyl nitrate, 0.18 ± 0.05; 1-butyl nitrate, 1.42 ± 0.11; 2-butyl nitrate, 0.69 ± 0.10; 2-pentyl nitrate, 1.87 ± 0.12; 3-pentyl nitrate, 1.13 ± 0.20; 2-hexyl nitrate, 3.19 ± 0.16; 3-hexyl nitrate, 2.72 ± 0.22; 3-heptyl nitrate, 3.72 ± 0.43; and 3-octyl nitrate, 3.91 ± 0.80. These rate constants, which are the first reported for the alkyl nitrates, are significantly lower than those for the parent alkanes, and a formula, based on the numbers of the various types of C—H bonds in the alkyl nitrates, is derived for rate constant estimation purposes.
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  • 22
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    International Journal of Chemical Kinetics 14 (1982), S. 933-944 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The literature results for the pyrolysis of bis trifluoromethyl peroxide are reexamined and compared with those for dimethyl peroxide. The thermochemistry yields the result that the π-bond energy in carbonyl fluoride is 96 ± 10 kcal/mol compared to 74 kcal/mol for that in formaldehyde. Thermodynamic additivity contributions are derived for the C—(F)3(O) and O—(C)(F) groups. Some conclusions are drawn in relation to the oxidation of halogeno methyl radicals and the chemistry of the atmosphere.
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    International Journal of Chemical Kinetics 14 (1982), S. 927-932 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aqueous iodination of trans-2-butenoic acid proceeds via hydrolysis of I2 to form HOI and I-, then rapid addition of HOI across the double bond to form the iodohydrin product. In the presence of iodate to keep iodide concentration low, the reaction proceeds at a conveniently measurable rate. The rate for the addition reaction \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm HOI + CH}_{\rm 3} {\rm CH=\!=CHCOOH} \to {\rm CH}_{\rm 3} {\rm CH(OH)CHICOOH}$$ \end{document} is -d[C4H6O2]/dt = 5900 [H+][C4H6O2][HOI]M/s at 25.0°C when [IO3-] = 0.025M and ionic strength = 0.3. The overall rate law in the presence of iodate is \documentclass{article}\pagestyle{empty}\begin{document}$$ -d[{\rm I}_{\rm 2}]/dt = 3.2 \times 10^{ - 3} \times 10^{ - 3} [{\rm H}^{\rm + }][{\rm IO}_{\rm 3}^ -]^{0.65} [{\rm C}_{\rm 4} {\rm H}_{\rm 6} {\rm O}_{\rm 2}]^{1/2} [{\rm I}_{\rm 2}]^{1/2} M/{\rm s}$$ \end{document} where [H+] and [IO3-] are total concentrations used to prepare the solution.
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  • 24
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    International Journal of Chemical Kinetics 14 (1982), S. 945-952 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of gas-phase decomposition of methyl isocyanate have been investigated in the range of 427-548°C. Two decomposition routes are followed; the predominant one is a radical-chain process giving CO, H2, and HCN as major products, which has an order of 1.5 and an Arrhenius equation given by log k(L1/2/mol1/2·s) = (13.12 ± 0.06) - (56,450 ± 1670) cal/mol/2.303 RT. The minor route is the bimolecular formation of N,N′-dimethylcarbodiimide and CO2, which from the low activation parameters Ea = 31.6 kcal, A = 105.30 L1/2/mol1/2·s, and the reaction order of 1.57 appears to be heterogeneous.
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  • 25
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    International Journal of Chemical Kinetics 14 (1982) 
    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 14 (1982), S. 977-984 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyridiniumchlorochromate (PCC) oxidizes aniline and substituted anilines except nitro anilines smoothly in chlorobenzene-nitrobenzene mixtures in the presence of dichloroacetic acid. The reaction has unit dependence on each of the aniline, PCC, and dichloroacetic acid concentrations. Electron-releasing substituents accelerate the reaction, whereas electronwithdrawing groups retard the reaction, and the rate data obey Hammett's relationship. The reaction constant ρ is -3.75. Azobenzene and p-benzoquinone have been obtained as products. The observed experimental data have been rationalized in terms of the formation of an intermediate complex involving PCC-amine undergoing a rapid decomposition to products.
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  • 27
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    International Journal of Chemical Kinetics 14 (1982), S. 1007-1015 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of stabilized carbonium ions of setoglaucin, methyl violet, and ethyl violet with cyanide ions are largely catalyzed by the cationic micelles of cetyltrimethylammonium bromide (CTAB) in aqueous media. Added counterions (anions in this case) have strong inhibitory effects on the CTAB-catalyzed reactions in the following order: N3- 〉 NO3- 〉 Br- 〉 Cl- 〉 F- 〉 no salt. The inhibitory effects of the counterions have been attributed to the exchange between added anions and reagent (CN-) in the micellar media. The data have been analyzed by the model schemes, and mathematical formulations were developed. Various parameters associated with the exchange process, such as equilibrium exchange constant, number of surfactant molecules per substrate molecule, number of added anions, and a factor related to the binding of additives to the catalytic micellar aggregates, have been evaluated.
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  • 28
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics and mechanism of oxidation of iminodiacetic acid and N-methyliminodiacetic acid by aquasilver(II) and Ag(II)-2,2′-bipyridine complexes has been investigated. The results are discussed with reference to the active reaction pathways, the equilibrium quotient of the title reactions, the protolytic equilibria which involve the oxidizing complex, and the intrinsic self-exchange rates of the oxidants.
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  • 29
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    International Journal of Chemical Kinetics 18 (1986) 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 30
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    International Journal of Chemical Kinetics 18 (1986), S. 31-40 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrogen abstraction by 1-phenylethyl radicals (ṘH) from phenylmethyl-carbinol (HROH) and benzyl alcohol (H2R′OH) has been studied in the liquid phase at 120°C. 1-Phenylethyl radicals have been generated by thermal decomposition of azo-bis-1-phenyl ethane and the formation of ethylbenzene (RH2), acetophenone (RO), and 2,3-di-phenyl butane (R2H2) has been monitored during the reaction.In order to optimize the experimental conditions, a mechanism has been assumed for the various pathways of the disappearance of ṘH and by using estimated rate parameters a presimulation was performed.The relative rate constants obtained are: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\frac{{k_{\rm H} }}{{\sqrt {{\rm 2}k_t } }} = 1.4{\rm } \times {\rm }10^{ - 4} {\rm L}^{1/2} {\rm mol}^{ - 1/2} {\rm s}^{ - 1/2} } & {{\rm for}} & {{\rm HROH}} \\ \end{array} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {\frac{{k_{\rm H} }}{{\sqrt {{\rm 2}k_t } }} = 1.0{\rm } \times {\rm }10^{ - 4} {\rm L}^{1/2} {\rm mol}^{ - 1/2} {\rm s}^{ - 1/2} } & {{\rm for}} & {{\rm H}_{\rm 2} {\rm R'OH}} \\ \end{array} $$\end{document} where kH refers to the hydrogen abstraction while kt is the combination rate coefficient of the radicals ṘH.
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  • 31
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    International Journal of Chemical Kinetics 18 (1986), S. 59-82 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The experimental data for the reactions of oxygen atoms with methane, ethane, and neopentane at temperatures below ca. 600 K have been reexamined. In the case of CH4 and C2H6 reactions, detailed computer models have been assembled to test the assumptions regarding stoichiometries that were made in the original studies in order to derive elementary rate coefficients from the experimentally observed reaction rates. It was found in both cases that the measurements are especially sensitive to secondary reactions not taken into account and impurities in the reagent alkane. Because the original reports did not include sufficient experimental details, it is not now possible to correct their results quantitatively. However, it appears, qualitatively, that the values for the O + CH4 and O + C2H6 rate coefficients were overestimated by factors of approximately 2 to 3 in the 250-400 K temperature range, with the error increasing as T decreases. Although the experimental results for the O + neopentane reaction are not as sensitive to the same kinds of complications, a comparison of the low-temperature measurements with those for the O + ethane reaction suggests that the previously recommended rate coefficients, based on the data of Herron and Huie, are probably also too high by a factor of 2 to 3.
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  • 32
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present a kinetic study of the reactions of ground-state sodium atoms with the molecules CH3F, CH3Cl, CH3Br, HCl, and HBr at elevated temperatures (537-966 K). Na(32S1/2) was generated by the pulsed irradiation of various sodium halide vapors and monitored by time-resolved atomic resonance absorption of the unresolved D-lines at λ = 589 nm [Na(32PJ) ← Na(32S1/2)] in the “single-shot mode.” The photoelectric signals were amplified without distortion, captured, and digitized in a transient recorder interfaced to a microcomputer for data analysis. Absolute second-order rate constants were measured at various temperatures in each case, yielding the following Arrhenius parameters (kRX = A exp(-E/RT), errors 1σ): which constitute, to the best of our knowledge, the first direct measurements of these quantities. The reaction between Na and HBr demonstrated anomalous behaviour which is discussed in terms of potential surfaces that have been calculated previously for this type of collisional process. The data are compared with analogous results for Na + CF4, CF3Cl, and CF3Br and with single-temperature measurements on diffusion flames.
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  • 33
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    International Journal of Chemical Kinetics 18 (1986), S. 145-158 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rate constants of various simultaneous reactions of t-butoxicarbonyl and t-butyl radicals generated by photolysis of t-butylpivalate in n-heptane are directly determined by kinetic electron spin resonance. The temperature dependence of the decarboxylation reaction t-BuOĊO → t-Bu. + CO2 obeys log )K/S-1( = 13.8-49.0/θ where θ = 2.303 RT/kJ . mol-1. The self- and cross-termination of the radicals are diffusion limited.
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  • 34
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    International Journal of Chemical Kinetics 18 (1986) 
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    Keywords: Chemistry ; Physical Chemistry
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  • 35
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    International Journal of Chemical Kinetics 18 (1986), S. 281-286 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction data described by the second-order growth function A(t) = A∞(αt) (1 + αt)-1, where A∞ is the ultimate value of the product concentration A(t), can be linearized by plotting a suitable function F(t) against the time (t). The slope of the straight line obtained is (2α), where α is the product of the rate constant (k2) and the initial concentration of either reactant, with the result that k2 can be determined without knowledge of Aϰ. Optimal determination of the parameter α requires that data taking be limited to the interval 0 ≤ t ≤ T, where (αT) is approximately 4.0. Numerical data derived from an experiment on the exchange of lead by zinc ions in the enzyme carbonic anhydrase are analyzed to illustrate the method. The effects of small errors in the initial concentrations and of small deviations from second-order kinetics are briefly discussed.
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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 stopped-flow technique has been used to study the effect of cationic (CTAN), nonionic (Triton X-100), andanionic (SDS) micelles on the rate of the reaction between nickel(II) ion and the ligand pyridine-2-azo-p-dimethylaniline (PADA) at 20.0°C and ionic strength 0.03 mol dm-3. The complex formation reaction is markedly inhibited by both CTAN and Triton X-100 micelles. The kinetic dataare found to conform to a reaction mechanism which implies only partitioning of the ligand between water and the micellar phase, the estimated bindingconstant of PADA being significantly larger in the presence of CTAN aggregates. Anionic micelles strongly speed the complexation reaction, Which occurs in the micellar phase with the same rate and the same mechanism as in water. The extent of binding of PADA to anionic micelles is similar to that found for the cationic micellar aggregates.
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  • 37
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    International Journal of Chemical Kinetics 18 (1986), S. 719-720 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 38
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    International Journal of Chemical Kinetics 18 (1986), S. 689-699 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxidation of primary alcohols by sodium N-chloroethylcarbamate in acid solution, results in the formation of corresponding aldehydes. The reaction is first order with respect to the oxidant and alcohol. The rate increases with an increase in acidity. The oxidation of α,α-dideuterioethanol exhibited a primary kinetic isotope, kH/kD = 2.11 at 298 K. The value of solvent isotope effect k(H2O)/k(D2O) = 2.23 at 298 K. Addition of ethyl carbamate does not affect the rate. (EtOC(OH)NHCl)+ has been postulated as the reactive species. Plots of (log k2 + Ho) against (Ho + log[H+]) are linear with the slope, φ, having values from 1.78-1.87. This suggested a proton abstraction by water in the rate-determining step. The rates of oxidation of alcohols bearing both electron-withdrawing and electron-donating groups are more than that of methanol. A concerted mechanism involving transfer of a hydride ion from the C—H bond of the alcohol tothe oxidant and removal of a proton from the O—H group by a water molecule has been proposed.
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  • 39
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    International Journal of Chemical Kinetics 18 (1986), S. 721-737 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical treatment is given for fast, multiple bond-switching reactions, such as NO + NH2 → N2 + H2O. These reactions are characterized by all or most of the bonds being broken. The collision complex involved (whether long or short lived) is shown to be extremely anharmonic. Consideration of the master equation describing the competing processes of complex formation, internal rearrangement and collisional deactivation yields easily applied sufficient conditions for the recombination rate coefficient being independent of pressure.
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  • 40
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    International Journal of Chemical Kinetics 18 (1986), S. 757-773 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rates of disproportionation of 0.015-0.4 mM aqueous glyoxal toglycolic acid were measured at 0.24-75 mM NaOH and constant ionic strength, leading to the empirical rate expression r = (a1[OH-] + a2[OH-]2) [GT]/(1 + a3[OH-]), where [GT] is the total glyoxal concentration. These results were confirmed in bicarbonate/carbonate buffer and at 2-20 mM [GT]. The rate form is in contradiction to earlier work on glyoxal, which suggested a second-order dependence on [OH-], but agrees with the rate equation for phenylglyoxal disproportionation. The kinetic data can be explained by a mechanism postulating the presence of monohydrated and dihydrated forms of glyoxal in equilibrium, with the rate-limiting steps being intramolecular hydride ion transfers to the unhydrated carbonyl carbon of the mono- and divalent anions of glyoxal monohydrate.
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  • 41
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    International Journal of Chemical Kinetics 18 (1986), S. 445-457 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction kinetics of carbon dioxide with four alkanolamines of industrial importance (MEA, DGA, DEA, and DIPA) have been investigated with the aid of the stopped-flow technique, allowing the determination of rate constants for carbamates formation. The constants obtained for MEA at 20°C and 25°C are in good agreement with recent literature data. The kinetic behavior of DGA was found to be almost identical to that of MEA.The rate constants obtained for DIPA at 25°C (54 M-1 s-1) is half as large as that for DEA (110 M-1 s-1). The former one is satisfactorily compared with the recent values proposed by Blauwhoff et al. Activation energies have also been obtained for DEA (23.2 kJ mol-1) and for DIPA (58.7 kJ mol-1) and their mechanistic implications are discussed in relation with the relevanceof a rate-determining proton transfer step in the process of carbamate formation.
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    International Journal of Chemical Kinetics 18 (1986), S. 497-504 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first stage thermal reactions of CF2CICH3 in the presence of chlorine have been studied between 554 and 614 K. These are and \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CF}_{\rm 2} {\rm CICH}_{\rm 3} {\rm + CI}_{\rm 2} \to {\rm CF}_{\rm 2} {\rm CICH}_{\rm 2} {\rm CI + HCI} $$\end{document} Rate equations derived from a radical mechanism are shown to fit the experimental results. Values of Arrhenius parameters for the decomposition of the CF2ClCH2. radical and its reactions with Cl2 and Cl are given.
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  • 43
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    International Journal of Chemical Kinetics 18 (1986), S. 829-836 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of diethyl ether was studied in the temperature range 697.2-760.5 K. The rate constant of reaction (1), and the ratio of the rate constant of reaction (2) to that of (12): were calculated from the amounts of products: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_1 ({\rm s}^{{\rm - 1}}) = (17.2 \pm 0.6) - (82.4 \pm 2.0{\rm kcal mol}^{{\rm - 1}})/2.3RT $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_2 /k_{12^{1/2} } ({\rm dm}^{{\rm 3/2}} {\rm mol}^{{\rm - 1/2}}) = (4.1 \pm 0.4) - (11.9 \pm 1.3{\rm kcal mol}^{{\rm - 1}})/2.3RT $$\end{document}
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    International Journal of Chemical Kinetics 18 (1986), S. 861-869 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chromatographic retention of H and D atoms has been observed in a quartz tube using argon as a carrier gas for D and six different gases for H. The results give equilibrium constants for the reversible adsorption of H and D on quartz as well as the rates of desorption. Self-consistent conclusions can be drawn from the data. The adsorption energy appears to be ca. 50 kJ mol-1 indicating weak chemisorption. The observations are consistent with vibration frequencies on the surface of around 700-900 cm-1 for D. and around 1000-1300 cm-1 for H. It appears that only a fraction of the surface atoms (ca. 10-2) act as adsorption sites.
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    International Journal of Chemical Kinetics 18 (1986), S. 871-884 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bimolecular reactions in the title were measured behind shock waves by monitoring the O-atom production in COS—O2—Ar and CS2—O2—Ar mixtures over the temperature range between 1400 and 2200 K. A value of the rate constant for S + O2 → SO + O was evaluated to be (3.8 ± 0.7) × 1012 cm3 mol-1 s-1 between 1900 and 2200 K. This was connected with the data at lower temperatures to give an expression k2 = 1010.85 T0.52 cm3 mol-1 s-1 between 250 and 2200 K. An expression of the rate constant for CS2 + O2 → CS + SO2 was obtained to be k21 = 1012.0 exp(-32 kcal mol-1/RT) cm3 mol-1 s-1 with an error factor of 2 between 1500 and 2100 K.
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  • 46
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    International Journal of Chemical Kinetics 18 (1986) 
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    Keywords: Chemistry ; Physical Chemistry
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  • 47
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    International Journal of Chemical Kinetics 18 (1986), S. vi 
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    Keywords: Chemistry ; Physical Chemistry
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  • 48
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    International Journal of Chemical Kinetics 18 (1986), S. 907-917 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the gas phase reaction between NO2 and CF2CCl2 has been investigated in the temperature range from 50 to 80°C. The reaction is homogeneous. Three products are formed: O2NCF2CCl2NO2 and equimolecular amounts of CINO and of O2NCF2C(O)Cl. The rate of consumption of the reactants is independent of the total pressure, the reaction products, and added inert gases and can be represented by a second-order reaction: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm NO}_{\rm 2}]}}{{dt}} = - 2\frac{{d[{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2}]}}{{dt}} = k[{\rm NO}_{\rm 2}][{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2}] $$\end{document}However, the distribution of the products is influenced by the pressure of the present gases, which favor the formation of the dinitro-compound in a specific way. The effect of CF2CCl2 is the greatest. In the absence of added gases, the ratio of O2NCF2CCl2NO2 to that of O2NCF2C(O)Cl is proportional to (CF2CCl2 + γP products).The experimental results can be explaned by the following mechanism: P and X represent the products and the added gases: \documentclass{article}\pagestyle{empty}\begin{document}$$ - \frac{{d[{\rm NO}_{\rm 2}]}}{{dt}} = - 2\frac{{d[{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2}]}}{{dt}} = k_1 [{\rm NO}_{\rm 2}][{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2}] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = 3.16 \pm 0.5 \times 10^6 \exp ( - 10500 \pm 1000{\rm cal/}RT){\rm M}^{{\rm - 1}} {\rm s}^{{\rm - 1}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \gamma }_{{\rm CF}_{\rm 2} {\rm CCI}_{\rm 2} } :{\rm \gamma }_P :{\rm \gamma }_{{\rm C}_{\rm 2} {\rm F}_{\rm 5} {\rm CI}} :{\rm \gamma }_{{\rm CCL}_{\rm 3} } :{\rm \gamma }_{{\rm CF}_{\rm 4} } :{\rm \gamma }_{{\rm N}_{\rm 2} } = 1:0.22:0.15:0.14:0.054:0.015 $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \gamma }_{{\rm NO}_{\rm 2} } 〈 0.01 $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_3 = 1.4 \pm 0.3 \times 10^8 {\rm s}^{{\rm - 1}} $$\end{document}
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    International Journal of Chemical Kinetics 18 (1986) 
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    International Journal of Chemical Kinetics 18 (1986), S. 739-755 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We develop a kinetic model for the exchange of tritium and deuteriumbetween tritium-containing heavy water and deuterated chloroform in a two-phase liquid system, catalyzed by hydroxide ion (sodium hydroxide). For the exchange reaction yielding tritiated chloroform andheavy water, the measured equilibrium constant is 0.518 at 25-45°C, independent of temperature. The rate constant (for the controlling step, deuteron abstraction from chloroform) is 0.22 L/mol s at 25°C, 0.72 at 35°C, and 2.0 at 45°C, corresponding to an activation energy of 87 kJ/mol. Comparison is made with literature data, and effects of mass transfer on the apparent rate constant are discussed.
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    International Journal of Chemical Kinetics 18 (1986), S. 775-789 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Equilibria and rates of interconversion between monomeric and dimeric glyoxal were measured in aqueous solution. The equilibrium constant [G2]/[G1]2 was 0.56 M-1 at 25°C, and was hardly affected by changes of ionic strength and pH but increased rapidly with increase of temperature. The rate of depolymerization was first-order in dimer, with the pseudo first-order rate coefficient in the pH range 1.3-7.8being of the form b1[H3O+] + b2 + b3[OH-]/(1 + b4[OH-]) + b5[OH-]. Coefficients b1 and b2 were more strongly affected by changes of temperature, though [OH-] was much the more effective catalyst. This rate form has not previously been observed for monomer-dimer inter-conversion of α-hydroxycarbonyls and α-dicarbonyls or for related reactions such as mutarotations and hydrations. Equivalent rate forms arisefrom reactions where an intermediate at steady state and low concentration is produced.
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    International Journal of Chemical Kinetics 18 (1986) 
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    Keywords: Chemistry ; Physical Chemistry
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  • 53
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    International Journal of Chemical Kinetics 18 (1986), S. 819-827 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An upper limit for the reaction rate of CO with the nitrate radical NO3 has been determined equal to 4 × 10-19 cm+3 molec-1 s-1 at 295 ± 2 K. In the experiment the isotopic species C13O16 and C13O18 mixed at 1-2 ppmv level in synthetic air have been reacted with NO3 and the reaction followed using long path infrared absorption FT spectroscopy. The result is of interest in the studies on the role played by NO3 in nighttime tropospheric chemistry.
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    International Journal of Chemical Kinetics 18 (1986), S. 837-846 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the gas phase reaction of OH radicals with dimethyl sulfide (CH3SCH3) have been studied at various temperatures and total pressures using two relative rate methods and a flash photolysis technique. For the relative rate methods, rate constants were measured at 296 ± 2 K as a function of the O2 pressure at a total pressure of ca. 740 torr. Data from these three experimental techniques were not in agreement. It is concluded that the relative rate techniques are subject to secondary reactions, possibly involving CH3S radicals. A rate constant of (2.5-0.6+0.9) × 10-12 e(130 = 102)/T cm3 molecule-1 s-1 obtained using the flash photolysis-resonance fluorescence data in the absence of O2, and which is in agreement with the lower range of values previously reported in the literature, is recommended.
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    International Journal of Chemical Kinetics 18 (1986), S. 847-859 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constant k1 for the reaction of OH radicals with CIO2 molecules was measured in a discharge flow system over the temperature range 293 ≤ T ≤ 473 K and at low pressures, 0.5 ≤ P ≤ 1.4 torr, using electron paramagnetic resonance or laser-induced fluorescence to monitor the pseudo first-order decay of OH concentrations. At 293 K, the value obtained for k1 was (7.2 ± 0.5) × 10-12 cm3 molecule-1 s-1. Within the temperature range of this study, a negative temperature dependence was observed: k1 = (4.50 ± 0.75) × 10-13 exp[(804 ± 114)/T] cm3 molecule-1 s-1. HOCl was detected by mass spectrometry as a product of the reaction and was titrated using OH + Cl2 as a source in the calibration experiments. A simulation of the mechanism of the OH + ClO2 reaction indicated that HOCl was mainly produced in the first reaction step. Both this result and the observed T dependence of k1 suggest that this reaction proceeds via an intermediate adduct with a cyclic geometry.
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  • 56
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    International Journal of Chemical Kinetics 18 (1986), S. 1023-1045 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The barrier for the hydrogen exchange reaction increases with the bend angle of H3. The implications for the dynamics of the reaction are explored on two levels. The static one uses the concept of a relaxed potential. This provides for a convenient, yet realistic representation. Itallows for the response of the molecule to the approaching atom. Among features made very evident by the relaxed potential is the possibility that hotH atoms can react by insertion. It also shows the widening of the cone of acceptance upon reagent vibrational excitation. On the dynamical level, classical trajectory computations are used to illustrate the dependence of the reactivity on the angle of attack and on the translational and vibrational excitation of the reagents. Detailed product distributions are generally not sensitive to the attack angle. An exception is the HD/H2 branching ratio in H + HD reactive collisions.
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  • 57
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    International Journal of Chemical Kinetics 18 (1986), S. 1277-1288 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have studied the oxidation of benzyl alcohols by nitrous and nitric acid in sulfuric acid media. The oxidation by nitrous acid is rapid and has an activation energy of 10.6 ± 0.8 kcal mol-1. A Hammett plot of logk2 vs. σ+ is linear with a ρ value of -1.4. The oxidation by nitric acid in sulfuric acid media is autocatalytic. From the kinetic and product analyses, it is concluded that a common oxidant, the nitrosonium ion is involved when either nitrous or nitric acid is used. A mechanism is proposed which involves the abstraction of hydride from the alcohols as the rate determining step. It is demonstrated that the autoxidation of the alcohols is catalyzed by nitrous acid or nitric oxide.
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    International Journal of Chemical Kinetics 18 (1986), S. 1303-1314 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rate constant of the reaction between OH and OCS in helium over the temperature range 255-483 K has been determined using the discharge flow-resonance fluorescence technique. The OCS has been carefully purified to avoid interference from H2S and CO impurities. An FTIR with a multireflection cell was used to determine the impurity concentrations and the purified sample was found to contain less than 0.005% of H2S. At 300 K, the rate constant was determined to be (2.0 ±0.40.8) × 10-15 cm3 molecule-1 s-1. Although the rate constants showed slight positive deviation at lower temperatures, thev can be satisfactorily fitted by the Arrhenius equation, k = 1.13 × 10-13 exp(-1200/T) cm3 molecule-1 s-1. No pressure dependence was observed at all temperatures, nor was O2 enhancement observed under our experimental conditions.
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    International Journal of Chemical Kinetics 18 (1986), S. 1333-1340 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas phase thermal isomerization of 4-acetyl-5-methyl-isoxazole affords 3-cyano-2,4-pentanedione as the only product in good agreement with previous proposed isomerization mechanism for isoxazoles. On the other hand, kinetic parameters and MO theoretical calculations do not agree with those previously reported. An alternative reaction mechanism which explains this fact is discussed.
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    International Journal of Chemical Kinetics 19 (1987), S. 457-486 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A chemical kinetic reaction mechanism has been developed which describes the oxidation of propanal within the temperature range 400-700 K. This mechanism has been tested against data obtained by four experimental groups over a wide range of initial conditions. The induction period and the absolute rate of propanal consumption are predicted to within a factor of 2 for initial densities of oxygen and propanal ranging over factors of 400. The existence and location of the negative temperature coefficient in the consumption of propanal are also simulated properly. The yields of all major and most minor products are predicted to within a factor of 2 for the wide variety of initial conditions tested. Sensitivity analyses were carried out at 553 and 713 K to identify the reactions primarily responsible for controlling the rate of propanal consumption and the distribution of products.
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    International Journal of Chemical Kinetics 19 (1987), S. 503-512 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction IO + CH3SCH3 → products (3) was studied at room temperature and near 1 Torr pressure of He, using the discharge flow mass spectrometric technique. The rate constant was found to be k3 = (1.5 ± 0.5) × 10-11 cm3 molecule-1 s-1. CH3S(O)CH3 was detected as a product suggesting the following channel: IO + CH3SCH3 → CH3S(O)CH3 + I. The rate constant of the reaction IO + IO → products (1) was also measured: k1 = (3 ± 0.5) × 10-11 at 298 K and 1 Torr pressure. The atmospheric implication of reaction (3) is discussed. The results indicate that this reaction could be a potential important sink of CH3SCH3 in marine atmosphere.
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    International Journal of Chemical Kinetics 18 (1986), S. 1215-1234 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The unimolecular decomposition of 2,2 dimethyloxetance to give either isobutence and formaldehyde or ethene and acetone induced by a pulsed CO2 laser has been investigated. Absorption characteristics and fractional decomposition have been studied as a function of laser fluence, irradiation frequency, reactant pressure, and added inert bath gas. Both absorption cross section and fractional decomposition are approximately independent of pressure of 2,2-dimethyloxetane below 50 times; 10-3 torr and increase with pressure at higher pressures of 2,2-dimethyloxetane. At pressures sufficiently low that collisions are negligible during the laser pulse, added inert gases reduce the amount of decomposition. Calculations of the fractional decomposition have been carried out based on RRKM theory and assuming either a Boltzmann or a Poisson intermolecular energy distribution. Master equation calculations of both absorption and decomposition for 10R20 irradiation have also been performed. Agreement between observed and calculated results for 10R20 irradiation could be obtained only by assuming that most, but not all, of the molecules in the irradiated volume absorb the laser radiation. Differences between the absorptions of the 10R20 and 9P20 lines and in the resulting extents of decomposition indicate that the fraction of irradiated molecules which absorbs 9P20 radiation is smaller than the fraction which absorbs 10R20 radiation.
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    International Journal of Chemical Kinetics 18 (1986) 
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    Keywords: Chemistry ; Physical Chemistry
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    Topics: Chemistry and Pharmacology
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    International Journal of Chemical Kinetics 18 (1986), S. 1289-1302 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the reaction between nitric oxide and chlorine have been investigated in both carbon tetrachloride and glacial acetic acid. The nitric oxide-oxygen reaction has been investigated in carbon tetrachloride.The appearance of product, NOCl or NO2, was monitored spectrophotometrically at a wavelength of 475 nm for NOCl and 343 nm for NO2. These measurements were performed using an Amino-Morrow stopped-flow apparatus equipped with a Beckman D U monochromator.The data for both the NO—Cl2 and NO—O2 systems could be fitted to the third-order integrated equation and the calculated rate constants were 2.75 × 103 M-2 s-1 and 2.79 × 106 M2 s-1, respectively, at 25.1°C.There was a noted increase in rate constants on changing the solvent from carbon tetrachloride to acetic acid.The likelihood of a termolecular encounter is inherent in the mechanism, however, no real evidence to substantiate either a direct termolecular or a series of two bimolecular steps has been obtained, although a -7 kcal for ΔH0 would support the latter.
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    International Journal of Chemical Kinetics 18 (1986), S. 1315-1321 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Trichloromethylperoxyl radicals were produced by pulse radiolysis of air saturated solutions containing CCl4. The rate constants for the reaction of CCl3O2 radicals with zinc tetraphenylporphyrin (ZnTPP) were determined in various solvents. They were found to vary between 3 × 107 and 3 × 109 M-1 s-1. The changes in rate constants result from complexation of ZnTPP with the different solvents, but did not correspond to changes in redox potential of ZnTPP. The rate constants were found to depend on the strength of the axial complexation, indicating an inner sphere mechanism whereby the radical binds to the metal prior to electron transfer.
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    International Journal of Chemical Kinetics 18 (1986), S. 1323-1331 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal addition of CF3O3CF3(T) to CF2CCl2(E) has been investigated between 49.6 and 69.5°C. The initial pressure of CF3O3CF3 was varied between 7 and 240 torr and that of CF2CCl2 between 4 and 600 torr. Four products of formula CF3O(E)j OOCF3, where j = 1 → 4 are formed. The sum of the products Σi = 14 CF3O(E)jOOCF3 is equal to the amount of trioxide decomposed.The reaction is homogeneous. Its rate is not affected by the total pressure and the presence of inert gas. It is a free radical telomerization with four basic steps: thermal decomposition of CF3O3CF3 into CF3O. and CF3O2., chain initiation by addition of CF3O. to olefin incorporated in, and telomeric radicals termination.The consumption of alkene is well represented by the equation: \documentclass{article}\pagestyle{empty}\begin{document}$$ - d[E]/dt = k_1 [T]\left\{ {1 + \sum\limits_{j = 1}^3 {\prod\limits_{i = 1}^j {[1 + (k_{t_1 } k_1^{1/2} /k_{gi} } k_t^{1/2})([T]^{1/2} /[E])]^{ - 1} } } \right\} $$\end{document} where (d[E]/d[T]) = \documentclass{article}\pagestyle{empty}\begin{document}$$ \bar n $$\end{document} is the mean chain length of telomerization. \documentclass{article}\pagestyle{empty}\begin{document}$$ \bar n $$\end{document} varies from 1.45 at 1.5 torr of E to 3.3 at 400 torr of E. Above this pressure E has no influence on \documentclass{article}\pagestyle{empty}\begin{document}$$ \bar n $$\end{document}.The estimated value of the constant for the addition of telomeric radicals to alkene is:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_g \simeq 8.6 \pm 6.0 \times 10^4 \exp ( - 2300 \pm 200{\rm col mol}^{{\rm - 1}} /RT){\rm M}^{{\rm - 1}} {\rm s}^{{\rm - 1}} $$\end{document}
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    International Journal of Chemical Kinetics 19 (1987), S. 49-60 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The rates of migration of acetyl, propionyl, isobutyryl, and benzoyl substituent in Diels-Alder adducts of acyl-1, 4-benzoquinones, (enediones), (I), to form the corresponding 2-acyl hydroquinones, (II), in 50% (v/v) ethanolic pyridine have been studied in detail. Rate dependence on pyridine concentration has been established and maximum rate was found at pyridine a volume percent of 25 in an ethanolic reaction mixture. The study indicated first-order dependence on reactants and fractional dependence on pyridine concentration. The effect of substituents of the acyl group on the rate showed that electronic factors play an important role on the stability of the transition state. A plausible mechanism, which is consistent with the results has been postulated and suitable rate law in consonance with the postulated mechanism have been derived.
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    International Journal of Chemical Kinetics 19 (1987), S. 61-79 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of acetonitrile was studied behind reflected shocks in a single pulse shock tube over the temperature range 1350-1950 K at overall densities of approximately 3 × 10-5 mol/cc. Methane and hydrogen cyanide are the major reaction products. They are formed by an attack of H and CH3 radicals on acetonitrile. The initiation step of the pyrolysis is the self dissociation of acetonitrile: for which the following rate constant was obtained: k1 = 6.17 × 1015exp(-96.6 × 103/RT)sec-1. Where R is given in units of cal/K mol. Additional reaction products which appear in the pyrolysis are: C2H2, C2H4, CH2=CHCN, CH≡CHCN, C2H5CN, C2N2, and C4H2. Acetylene is formed from methane pyrolysis and becomes a major reaction product at high temperatures. Acrilonitrile and cyanoacetylene are secondary products originating from the CH2CN radical. Rate parameters for the formation of the reaction products are given.
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    International Journal of Chemical Kinetics 19 (1987), S. 115-128 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acetylperoxy radicals were produced by the flash photolysis of chlorine in the presence of acetaldehyde and oxygen. By adding various concentrations of nitrogen dioxide, the rate constant for the reaction producing PAN was measured to be k4 (153 Torr) = (2.29 ± 0.05) × 109 L/mol s.The effect of pressure has been studied over the range 76-612 Torr and the data fitted to a fall-off curve with k4∘ = 1.85 × 1013 L2/mol2 s. and k4x = 3.67 × 109 L/mol s. With a calculated value of the dissociation constant, k-4∘ = 268 L/mol s and of the equilibrium constant, K4 = 1.04 × 1012 L/mol, the expected strong collision value for k4∘ is 2.79 × 1014 L2/mol2 s.The ultraviolet absorption spectrum of PAN has been characterized in the range 205-260 nm.
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    International Journal of Chemical Kinetics 14 (1982), S. 399-416 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recent experimental results on the thermal decomposition of N2O5 in N2 are evaluated in terms of unimolecular rate theory. A theoretically consistent set of fall-off curves is constructed which allows to identify experimental errors or misinterpretations. Limiting rate constants k0 = [N2] 2.2 × 10-3 (T/300)-4.4 exp(-11,080/T) cm3/molec·s over the range of 220-300 K, k∞ = 9.7 × 1014 (T/300)+0.1 exp(-11,080/T) s-1 over the range of 220-300 K, and broadening factors of the fall-off curve Fcent = exp(-T/250) + exp(-1050/T) over the range of 220-520 K have been derived. NO2 + NO3 recombination rate constants over the range of 200-300 K are krec,0 = [N2] 3.7 × 10-30 (T/300)-4.1 cm6/molec2·s and krec,∞ = 1.6 × 10-12 (T/300)+0.2 cm3/molec·s.
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    International Journal of Chemical Kinetics 14 (1982), S. 381-397 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of the gas-phase elimination of several chloroesters were determined in a static system over the temperature range of 410-490°C and the pressure range of 47-236 torr. The reactions in seasoned vessels, and in the presence of a free-radical inhibitor, are homogeneous, unimolecular, and follow a first-order law. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for methyl 3-chloropropionate, log k1(s-1) = (13.22 ± 0.07) - (231.5 ± 1.0) kJ/mol/2.303RT; for methyl 4-chlorobutyrate, log k1(s-1) = (13.31 ± 0.25) - (221.5 ± 3.4) kJ/mol/2.303RT; and for methyl 5-chlorovalerate, log k1(s-1) = (13.12 ± 0.25) - (221.7 ± 3.2) kJ/mol/2.303RT. Rate enhancements and lactone formation reveal the participation of carbonyl oxygen of the carbomethoxy group. The order COOCH3-5 〉 COOCH3-6 〉 COOCH3-4 in assistance is similar to the sequence of group participation in solvolysis reactions. The partial rates for the parallel eliminations to normal dehydrohalogenation products and lactones have been estimated and reported. The present results lead us to consider that an intimate ion-pair mechanism through participation of the carbomethoxy group may well be operating in some of these reactions.
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    International Journal of Chemical Kinetics 14 (1982), S. 517-534 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Many experiments in chemical kinetics are initiated by a fast pulse, such as electric discharge, shock wave, flash lamp, or laser. After this pulse one observes the production and subsequent decay of a reactive intermediate. One then postulates a mechanism and adjusts the associated rate constants so as to minimize the difference between the results of the experiment and the prediction of the mechanism. The parameters to be estimated are usually strongly correlated, so that it is not possible to determine them separately. These estimated parameters are of little value unless we can also estimate statistically valid confidence limits for them. The difficulties are discussed which frequently arise in estimating parameters and confidence limits for a kinetic mechanism which is widely used in interpreting laser excitation and fluorescence measurements, that is, first-order production and decay. These difficulties, and methods for dealing with them, are illustrated with realistic data. The estimation problem is particularly ill conditioned when the production and loss rates are nearly equal. In some experimental systems this can be avoided, but in others it is inevitable.
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    International Journal of Chemical Kinetics 14 (1982), S. 535-541 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is proposed whereby the orders and rate constants for processes obeying the rate law -dA/dt = kAn may be determined. The method is illustrated in two ways. First, simulated data for processes of various orders are treated, and the treatment is shown to be capable of reproducing orders and rate constants to a high degree of accuracy. The factors affecting the accuracy with which n and k can be determined are considered. These are inaccuracy in the determination of concentration values, irregularity of the time intevals between concentration determinations, and the length of those time intervals. It is shown that if concentrations are determined at times that are close together, the effect of the other two factors is small, but if the time intervals are made longer, the errors due to the other two factors affect the calculated values of n and k much more seriously. Second, the method was applied to two homogeneous reactions, of which one was first-order and one was second order, and three heterogeneous reactions, of which one was found by the original workers to be first order, one to be zero order, and one to vary between zero and first order, depending on the initial pressure. The present method gives results in agreement with these conclusions and reproduces the rate constants to within ±5% in all cases.
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    International Journal of Chemical Kinetics 14 (1982), S. 565-583 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results are reported from moderated nuclear recoil 18F experiments with the 273 K CHF3/C3F6/C2F6 system. Although the measurement sensitivity is only about ±12%, there is no evidence to support the occurrence of nonthermal F-to-HF reactions at 95 mol % C2F6 moderator concentration.
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    International Journal of Chemical Kinetics 14 (1982), S. 543-564 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The main difference between the simple RRK theory and the better based but more complex RRKM theory is explained. Starting from the premise that the classical versus quantum mechanical estimation of the density of states is the major source of the difference, earlier attempts to incorporate the quantum effects in an effective value for the number of oscillators s are noted. By examining the expression for the RRKM rate coefficient it is found that a single effective s value will generally not suffice, but a much better representation of the quantum effects can be obtained if it is recognized that the problem inherently contains two different effective s values. A theory based on this analysis is constructed. It reproduces RRKM results to much improved accuracy, removing difficulties found earlier with single-s-value theories.
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    International Journal of Chemical Kinetics 14 (1982), S. 613-621 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal unimolecular decomposition of pent-2-yne has been studied over the temperature range of 988-1234 K using the technique of very low-pressure pyrolysis (VLPP). The main reaction pathway is C4—C5 bond fission producing the resonance-stabilized 3-methylpropargyl radical. There is a concurrent process producing molecular hydrogen and penta-1,2,4-triene presumably via the intermediate formation of cis-penta-1,3-diene. The 1,4-hydrogen elimination from cis-penta-1,3-diene is the rate-determining step in the molecular pathway. This is supported by an independent VLPP study of cis- and trans-penta-1,3-diene. RRKM calculations show that the experimental rate constants for C—C bond fission are consistent with the following high-pressure rate expression at 1100 K: \documentclass{article}\pagestyle{empty}\begin{document}$$\log k_1 = \left({s^{ - 1}} \right) = \left({16.0 \pm 0.3} \right) - \left({72.6 \pm 2.0} \right)/\theta $$\end{document} where θ = 2.303RT kcal/mol and the A factor was assigned from the results of shock-tube studies of related alkynes. The activation energy leads to ΔHf,3000[CH3C≡CĊH2] = 70.3 and DH3000[CH3CCCH2—H] = 87.4 kcal/mol. The resonance stabilization energy of the 3-methylpropargyl radical is 10.6 ± 2.5 kcal/mol, which is consistent with previous results for this and other propargylic radicals.
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    Topics: Chemistry and Pharmacology
    Notes: An iterative method has been devised for the simulation of chemiluminescence data during the oxidative decomposition of αα′ azobisisobutyronitrile in the presence of ethylbenzene. From this simulation the cross termination rate constant of the two types of peroxy radicals present has been estimated.
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    International Journal of Chemical Kinetics 14 (1982), S. 659-668 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of gamma-radiation-induced free-radical reactions in carbon tetrachloride solutions of ethanol and n-pentanol were studied in the range of 0.05-0.80M and 25-170°C. The rate constant for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$${\rm CCl}_{\rm 3} + {\rm R} - CH_2 - {\rm OH}\mathop \to \limits^{k1} {\rm CHCl}_{\rm 3} + {\rm R} - {\rm CH} - {\rm OH}$$\end{document} was found as \documentclass{article}\pagestyle{empty}\begin{document}$$k1(M^{- 1} \cdot s^{- 1}) = 10^{8.6 \pm 0.4} \exp - (\frac{{9900 \pm 600{\rm cal}}}{{RT}})$$\end{document} The activation energy is larger by 0.8 kcal/mol than for secondary alcohols, while the A1 factors are about the same.
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  • 79
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    International Journal of Chemical Kinetics 14 (1982), S. 955-975 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dark-phase experiments between isoprene and O3 are discussed. UNC outdoor chamber experiments have shown that in high-concentration systems of isoprene and O3 (5 ppm C and 1 ppm) approximately 75% of the reacted carbon can be observed in the product formation of HCHO, CO, methacrolein, methylvinylketone, methylglyoxal, acetaldehyde, and propylene. Mechanisms were developed which gave reasonable fits to dark-phase chamber experiments of MACR, MVK, isoprene, and O3. Experimental data and modeling results were used to generate O3 rates of attack on MVK and MACR. An isoprene-O3 rate of 1.67 × 10-2 ppm-1·min-1 was used and is consistent with other rates reported in the literature. Dark isoprene-O3 systems appear to form homogeneously nucleated aerosol. Most of these particles appear and remain at diameters well below the optical cutoff region (0.3-0.5 μm), as opposed to the particles from similar α-pinene-O3 systems, which also form at smaller sizes but then grow into the optical size range (0.5 μm). Lower concentrations of α-pinene and O3 (0.2 ppm C and 0.12 ppm) still generated substantial aerosol, but by comparison, rapid CN nucleation was not observed during a similar side-by-side system of isoprene and O3.
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  • 80
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    International Journal of Chemical Kinetics 14 (1982), S. 985-996 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Time-resolved absorption spectra for a reaction mixture of p-methoxystyrene and tetracyanoethylene (TCNE) are found to have a band maximum at 325 nm which is assigned to the 1,4-cycloadduct. The reaction in chloroform at 15, 20, and 25°C is followed by the charge-transfer band at 600 nm. The 1,4-cycloadduct, besides the so far known 1,2-cycloadduct and EDA complex, is taken into account to derive the rate equation for the EDA complex that is a linear second-order differential equation. The rate constants for the elementary steps involved in the reaction are obtained. The 1,4-cycloaddition has an activation entropy of -63 J/K·mol for the cycloreversion and a reaction constant ρ of -4.7, both of which indicate the polar transition state. On the other hand, activation entropy of the 1,2-cycloaddition is 73 J/K·mol more negative than that of the 1,4-cycloaddition, supporting the zwitterionic mechanism for the 1,2-cycloaddition.
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  • 81
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    International Journal of Chemical Kinetics 14 (1982), S. 997-1005 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of acetylene (A) with cyclohexa-1,3-diene (CHD) has been studied between 450 and 592 K. The pressures of A ranged from 25 to 112 torr and those of CHD from 8 to 62 torr. The reaction yields only ethene (E) and benzene (B) instead of bicyclo[2.2.2]octa-2,5-diene (BOD), the product that is expected for a 1,4,1′,2′ addition of the Diels-Alder type. It is first order with respect to each reagent. The rate constant (in L/mol·s) is given by \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} k = - (27,150 \pm 120)/4.576T + (7.49 \pm 0.05)$$\end{document} The thermal decomposition of BOD has also been studied. In the ranges of 354-435 K and 0.5-6 torr, the reaction is first order and results in the formation of equal amounts of B and E as the reaction of A with CHD does. Its rate constant (in s-1) is given by \documentclass{article}\pagestyle{empty}\begin{document}$$\log _{10} k_d = - (32,520 \pm 40)/4.576T + (14.06 \pm 0.02)$$\end{document} The following consecutive reactions are proposed for the reaction between A and CHD: where BOD is the primary product that is too unstable to be detected. This implies that the rate constant k is equal to ka. The reaction mechanisms and the strain energy in BOD are discussed.
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  • 82
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    International Journal of Chemical Kinetics 14 (1982), S. 1105-1112 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Energetic hydrogen atoms generated by photolysis of HBr or HI react with CDCl3 by abstracting either a deuterium atom (1) or a chlorine atom (2): The integral probability of reaction (2) has been measured for several defined initial translational energies of H*, and the phenomenological threshold energy is 31 ± 14 kJ/mol. For initial translational energies in the range of 66-121 kJ/mol, the ratio of the integral probabilities of Cl abstraction and of D abstraction, when normalized to equal numbers of Cl and D atoms, is 2.4 ± 0.3. The interpretation of the integral reaction probabilities in terms of the excitation functions of reactions (1) and (2) is discussed. Measurements of the moderating effect of CO2 on reactions (1) and (2) show that CDCl3 is slightly more effective than CO2 as a moderator of H atoms in the energy range of 90-30 kJ/mol.
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  • 83
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    International Journal of Chemical Kinetics 14 (1982), S. 1165-1182 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results are reported from moderated nuclear recoil 18F experiments with the CH4/C3F6/C2F6 mixture system. At a 99.5% confidence level measurement precision of ±3.4%, non-thermal F-to-HF reactions are phenomenologically suppressed at C2F6 moderator concentrations in the range of 95.0-99.95 mol-%. Effectively equilibrium reaction conditions can be established in well-designed experiments of this type.
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  • 84
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    International Journal of Chemical Kinetics 14 (1982), S. 1199-1209 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction 2NO2 + ROH = RONO + HNO3 (R = CH3 or C2H5) has been studied using the FTIR method at reactant pressures from 0.1 to 1.0 torr at 25°C. The termolecular rate constant for the forward reaction was determined to be (5.7 ± 0.6) × 10-37 cm6/molec2·s for CH3OH and (5.7 ± 0.8) × 10-37 cm6/molec2·s for C2H5OH, that is, d[RONO]/dt = k[NO2]2[ROH]. The corresponding equilibrium constants were measured as 1.36 ± 0.06 and 0.550 ± 0.025 torr-1, respectively. These results are consistent with those of a previous study based on the NO2 decay measurements at reactant pressures from 1 to 10 torr.
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  • 85
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    International Journal of Chemical Kinetics 14 (1982), S. 1183-1197 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of oxidation of arginine, histidine, and threonine by chloramine-T (CAT) have been investigated in alkaline medium at 35°C. The rates are first order in both [CAT] and [amino acid] and inverse fractional order in [OH-] for arginine and histidine. The rate is independent of [OH-] for threonine. Variation of ionic strength and addition of the reaction product, p-toluenesulfonamide, or Cl- ions had no effect on the rate. A decrease of the dielectric constant of the medium by adding methanol decreased the rate with arginine, while the rates increased with histidine and threonine. The solvent isotope effect was studied using D2O. (kobs)D2O/(kobs)H2O was found to be 0.55 and 0.79 for arginine and histidine, respectively. The reactions were studied at different temperatures, and activation parameters have been computed. The oxidation process in alkaline medium, under conditions employed in the present investigations, has been shown to proceed via two paths, one involving the interaction of RNHCl (formed rapidly from RNCl-), with the amino acid in a slow step to form monochloroamino acid, which subsequently interacts with another molecule of RNHCl in a fast step to give the products, p-toluenesulfonamide (RNH2), and the corresponding nitrile of the amino acid (R'CN). The other path involves the interaction of RNCl- with the amino acid in a similar way to give RNH2 and R'CN. Mechanisms proposed and the derived rate laws are consistent with the observed kinetics. The rate constants predicted using the derived rate laws, as [OH-] varies, are in excellent agreement with the observed rate constants, thus justifying these rate laws and hence the proposed mechanistic schemes.
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  • 86
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    International Journal of Chemical Kinetics 14 (1982), S. 1211-1218 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rates of oxidation of XCOO- (X = H, D) by Br2 in acid aqueous media were measured between 274 and 332 K. The derived Arrhenius parameters for both reactions \documentclass{article}\pagestyle{empty}\begin{document}$$\log k_{\rm H} (M^{- 1} {\rm s}^{{\rm - 1}}) = (11.18 \pm 0.10) - (14.33 \pm 0.13)/\theta $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$\log k_{\rm D} (M^{- 1} {\rm s}^{{\rm - 1}}) = (13.77 \pm 0.13) - (17.62 \pm 0.04)/\theta $$\end{document} where θ = 4.575T × 10-3 kcal/mol, with (kH/kD)298K = 2.85, reveal a primary isotope effect, but the difference (ED - EH) = 3.29 kcal/mol and the ratio AD/AH = 91 fall beyond the limits imposed by semiclassical transition-state theory, suggesting tunneling or a multiple-stage mechanism. However, it can be shown that either tunneling in a single step or a three-step, internal return mechanism can be ruled out as alternative models, since both require unreasonable kinetic parameters to fit the data. The simplest scheme accounting for the present observations involves tunneling in the decomposition of a charge transfer complex in equilibrium with the reactants.
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  • 87
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    International Journal of Chemical Kinetics 14 (1982), S. 1219-1229 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Kinetic investigations on the reaction between U(IV) and H2O2 have been carried out at different acidities in chloride medium at an ionic strength of 2M. The observed bimolecular rate constant has been found to be dependant on [H+]-1.3. The activation energy of the overall reaction has been found to vary from 13.4 ± 0.7 to 18.0 ± 0.8 kcal/mol in the range of acidity from 0.3 to 1.5M. The results have been explained on the basis of three parallel rate-controlling reactions involving unhydrolyzed species of U(IV) and hydrolyzed species UCl(OH)2+ and UO2+. The values of the rate constants for these three reaction paths have been found to be of the order of 3.95, 5.59 × 103, and 1.49 × 105M-1 min-1, respectively.
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  • 88
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    International Journal of Chemical Kinetics 18 (1986), S. 227-239 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Study of the thermal decomposition of propane at very low conversions in the temperature range 760-830 K led to refinement of the mechanism of the reaction.The quotient VCH4 + C2H4/VH2 + C3H6 characterizing the two decomposition routes connected with the 1- and 2-propyl radicals proved to depend linearly on the initial propane concentration. This suggested the occurrence of intermolecular radical isomerization: in competition with decomposition of the 2-propyl radical: The linearity led to the conclusion that the selectivity of H-abstraction from the methyl and methylene groups by the methyl radical is practically the same as that by the H atom. The temperature-dependence of this selectivity ( μ = kCH3/kCH2) was given by\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm \mu = }\frac{{k_3 }}{{k_4 }} = \frac{{k_1 }}{{k_2 }} = 10^{0.26 \pm 0.03} \exp ( - 7.24 \pm 0.45{\rm kJ mol}^{{\rm - 1}} /RT). $$\end{document} Further evaluation of the dependence gave the Arrhenius representation \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{k_7 }}{{k_6 }} = 10^{ - 5.97 \pm 0.03} \exp (115 \pm 5.1{\rm kJ mol}^{{\rm - 1}} /RT){\rm mol}^{{\rm - 1}} {\rm dm}^{\rm 3} $$\end{document} for the ratio of the rate coefficients of the above isomerization and decomposition reactions.Steady-state treatment resulted in the rate equation of the process, comparison of which with measurements gave further Arrhenius dependences.
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  • 89
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    International Journal of Chemical Kinetics 18 (1986), S. 255-265 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conditions of applicability of quasi-steady-state kinetic treatment have been investigated with respect to the explanation of the decomposition of propane and the influence of ethylene on this.From the measured rate of accumulation of ethane and from the relations between the kinetic equations describing product formation, the rate parameters of the initiation reactions were determined, for which the temperature-dependences \documentclass{article}\pagestyle{empty}\begin{document}$$ k_i = 10^{17,05 \pm 0.99} \exp ( - 356 \pm 11{\rm kJmol}^{{\rm - 1}} /RT)s^{ - 1} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{ie} = 10^{12.0 \pm 0.99} \exp ( - 225 \pm 15{\rm kJmol}^{{\rm - 1}} /RT){\rm mol}^{{\rm - 1}} {\rm dm}^{\rm 3} s^{ - 1} $$\end{document} were found.In the decomposition of propane under the examined conditions, the chain length exceeds 500. In response to ethylene the chain length significantly decreases, but even in this case the decomposition chains are long enough for it to be assumed that the ratios of radical concentrations are governed by the propagation steps.Calculations demonstrated that the actual radical concentration during a sufficiently short induction period approximates to the stationary concentration, so that it does not seriously affect the accuracy of the kinetic treatment.
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  • 90
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    International Journal of Chemical Kinetics 18 (1986), S. 437-443 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrogen transfer reaction between C2H6 and CF3 radicals, generated by the photolysis of CF3I, has been studied in the temperature range 298-617 K. The rate constant, based on the value of 1013.36 cm3 mol-1 s-1 for the recombination of CF3 radicals, is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_2 = (11.90 \pm 0.09) - (33230 \pm 740)/19.145T $$\end{document} where k2 is in cm3 mol-1 s-1 and E is in J mol-1. These results are compared with those previously reported, and the following best value for k2 is recommended: \documentclass{article}\pagestyle{empty}\begin{document}$$ \log k_2 = (11.94 \pm 0.07) - (33670 \pm 540)/19.145T $$\end{document}
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  • 91
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    International Journal of Chemical Kinetics 18 (1986), S. 459-472 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of the effective potential energy curves on the calculation of the strong collision limiting low-pressure rate coefficients of thermal dissociation-recombination reactions was analyzed in terms of the factorized formalism of Troe. An analysis of 26 reactions employing a Morse potential coupled with a quasitriatomic molecular model and an explicit account of the adiabatic zero-point barriers, as originallyproposed by Troe, was performed. A comparison between calculations realizedwith an exactly fitted looseness parameter, α, and with a standard value of α = 1.0 Å-1, indicates that the use of this last value is satisfactorily justified in the evaluation of thestrong collision limiting low-pressure rate coefficients. A study interms of restrictive relationships between the looseness and Morse parameters and ab initio, radial potentials (for CH4, CH3O2, and HO2) was also realized. The uncertainties in the evaluation of termolecular rate coefficients due to the lack of a complete knowledge of the long-range potentials are also briefly discussed.
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  • 92
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    International Journal of Chemical Kinetics 18 (1986), S. 487-496 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate constants for the gas phase reaction of OH radicals with pyrrole (k1) and thiophene (k2) have been measured over the temperature ranges 298-440 and 274-382 K, respectively, using the flash photolysis-resonance fluorescence technique. The rate constants obtained were independent of the total pressure of argon diluent over the range 25-100 torr andwere fit by the Arrhenius expressions \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = (2.7 \pm _{0.6} ^{0.8}) \times 10^{ - 11} \exp [(403 \pm 93)/T]{\rm cm}^{\rm 3} {\rm molecule}^{{\rm - 1}} {\rm s}^{{\rm - 1}} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 = (1.2_{ - 0.6} ^{ + 1.0}) \times 10^{ - 12} \exp [(584 \pm 217)/]{\rm cm}^{\rm 3} {\rm molecule}^{{\rm - 1}} {\rm s}^{{\rm - 1}} $$\end{document} with rate constants at 298 ± 2 K of k1 = (1.03 ± 0.06) × 10-10 cm3 molecule-1 s-1 and k2 = (8.9 ± 0.7) × 10-12 cm3 molecule-1 s-1. [These errors represent two standard deviations (systematic errors could constitute an additional ca. 10% uncertainty)]. These results are discussed with respect to the previous literature data and the atmospheric lifetimes of pyrrole and thiophene.
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  • 93
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    International Journal of Chemical Kinetics 18 (1986), S. 529-536 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Following the kinetic investigation of the solvolysis of a range of cobalt(III) complexes in mixtures of water + cosolvent wherethe cosolvent enhances the solvent structure and decreases the dielectric constant, kinetic data are now reported for such a solvolysis in water + urea where urea acts as a structure breaker and enhances the dielectric constant. A plot of log (rate constant) against reciprocal of the dielectric constant shows that differential effects of changes in solvent structure occur between the initial and the transition states and, as in theinvestigations using structure-enhancing cosolvents, the principal effect of change in solvent structure on the cobalt(III) cation occurs on the penta-coordinated ion in the transition state.
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  • 94
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The abstraction of hydrogen and deuterium from 1,2-dichloroethane, 1,1,2-trichloroethane, and two of their deuterated analogs by photochemically generated ground state chlorine atoms has been investigatedin the temperature range 0-95°C using methane as a competitor. Rate constants and their temperature coefficients are reported for the following reactions Over the temperature range of this investigation an Arrhenius law temperature dependence was observed in all cases. Based on the adopted rate coefficient for the chlorination of methane [L.F. Keyser, J. Chem. Phys., 69, 214 (1978)] \documentclass{article}\pagestyle{empty}\begin{document}$$ k_r /{\rm cm}^{\rm 3} {\rm s}^{{\rm - 1}} = (1.65 \pm 0.32) \times 10^{ - 11} \exp [ - (1530 \pm 68)/T] $$\end{document} which is commensurate with the present temperature range, the following rate constant values (cm3 s-1) are obtained: \documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 = (4.93 \pm 0.96) \times 10^{ - 11} \exp [ - (1087 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_2 = (2.92 \pm 0.57) \times 10^{ - 11} \exp [ - (1362 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_3 = (2.39 \pm 0.57) \times 10^{ - 11} \exp [ - (1750 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_4 = (1.68 \pm 0.33) \times 10^{ - 11} \exp [ - (1965 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_5 = (1.22 \pm 0.24) \times 10^{ - 11} \exp [ - (1948 \pm 68)/T] $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_6 = (1.47 \pm 0.28) \times 10^{ - 11} \exp [ - (1910 \pm 68)/T] $$\end{document} The observed pure primary, and mixed primary plus α- and β3-secondary kinetic isotope effects at 298 K are k3/k6 = 2.73 ± 0.08, and k1/k2 = 4.26 ± 0.12, respectively. Both show a normal temperature dependence decreasing to k3/k6 = 2.39 ± 0.06 and k1/k2 = 3.56 ± 0.09 at 370 K. Contrary to some simple theoretical expectations, the kinetic isotope effect for H/D abstraction decreases with increasing number of chlorine substituents in the geminal group in a parallel manner to the trend established previously for C1-substitution in the adjacent group. The occurrence of a β-secondary isotope effect, k4/k5, is established; this effect suggests a slight inverse temperature dependence.
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  • 95
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    International Journal of Chemical Kinetics 18 (1986), S. 575-596 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal decomposition of propanoic acid dilute in argon has beenstudied in a single-pulse shock tube over the temperature range of 1100-1500 K and over the pressure range of 14-18 atm. The decomposition kinetics have been satisfactorily computer modelled by means of afree radical mechanism involving H and OH chains.Recent single-pulse shock tube product analyses of acetic acid decomposition have been computer modelled using a free radical mechanism for decarboxylation coupled to a unimolecular dehydration reaction.A comparison between the thermal decomposition kinetics of the C1—C3 alkanoic acids is made. The present studies do notprovide evidence for the participation of transition states involving a pentavalent carbon atom in the pyrolyses of the lower alkanoic acids.
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  • 96
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    International Journal of Chemical Kinetics 18 (1986) 
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    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 97
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    International Journal of Chemical Kinetics 18 (1986), S. 623-637 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unimolecular reactions of mutual isomerization of cyclopentyl and 1-penten-5-yl radicals have been investigated by chemical activation. The radicals were generated by adding energized hydrogen atoms (EH about 23 kcal mol-1) to the double bond of either cyclopentane or 1,4-pentadiene. Based on the extensive steady-state RRKM calculations employing the experimental data from this work as well as from the literature, the threshold energies for the cyclopentyl ring opening and closure are 32 ± 0.3 and 16.2 ± 0.3 kcal mol-1, respectively. The entropy of activation for the ring opening is close to zero.
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  • 98
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    International Journal of Chemical Kinetics 18 (1986), S. 655-688 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acetaldehyde oxidation has been studied in experiments at temperatures of 553 and 713 K carried out in a low pressure, static reactor and in numerical modeling calculations using a detailed chemical kinetic reaction mechanism. The results of the experimental study were used to construct and validate the reaction mechanism, which was then used to examine acetaldehydeoxidation in the negative temperature coefficient regime between 550 and 900 K. This mechanism was also tested against independent measurements of acetaldehyde oxidation carried out by Baldwin, Matchan, and Walker. The overall rate of reaction and the properties of the negative temperature coefficient regime were found to be sensitive to the competition between radical decomposition reactions and the addition of molecular oxygen to acetyl and methyl radicals, including particularly \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 3} + {\rm O}_2 + {\rm M = CH}_{\rm 3} {\rm O}_{\rm 2} + {\rm M} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 3} {\rm CO} + {\rm M = CH}_{\rm 3} {\rm + CO} + {\rm M} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 3} {\rm CO} + {\rm O}_{\rm 2} {\rm = CH}_{\rm 3} {\rm CO}_{\rm 3} $$\end{document} During these experiments, an upper limit to the rate of decomposition ofCH3O2H was measured at 553 K. Implications of the results for future kinetic modeling of engine knock are discussed.
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  • 99
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Procedures are discussed to correct for nonideality in a shock tube used in the reflected mode in conjunction with flash photolysis and atomic resonance absorption to measure chemical kinetics of atoms at high temperatures. Experimentally, pressure time profiles for the incident and reflectedshock regions are made close to the location of the observation windows through which absorbance is measured. The corresponding temperatures are calculated from the adiabatic equation of state. Justification for this procedure is provided by extending Mirels' boundary layer theory to take intoaccount interaction of the reflected wave with the flowing gas in the free stream and in the boundary layer. These theoretical methods are described for calculating the thermodynamic and hydrodynamic states behind the reflected wave from initial values of pressure and temperature and the measured velocity of the incident wave. The implication of these results to kinetic measurements at high temperature is discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 100
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactants, products, and saddle point for the reaction H2 + CN → H + HCN have been studied by ab initio calculations. The computed structures, frequencies, and energetics are compared directly to available measurements and, indirectly, to experimental rateconstants. The theoretical rate constants used in the comparison are calculated with conventional transition state theory. By reduction of the computed reaction barrier to 4.1 kcal mol,-1 good agreement with experimental rate constants is obtained over a 3250-K temperature range. This computed rate constant is well represented by the form 4.9 × 10-18 T2.45 e-1, 126/T over the temperature range of 250 K-3500 K. Substantial reaction rate curvature is found due to low-frequency bending modes at the saddle point. The results for this reaction are compared to other abstraction reactions involving H atom transfer to identify correlations between reaction exothermicity and both abstraction barriers and reaction rate curvature.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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