bluuebunny/crossref_metadata_2025_split huggingface dataset:
The kinetics of the gas phase intramolecular elimination of isobutene from 2‐d1‐triisobutylaluminum and the deuterium isotope effect in reactions involving cyclic transition states
Authors: Egger Kurt W. 
Published: January 2005

AbstractThe intramolecular elimination of isobutene from 2‐d1‐triisobutylaluminum has been studied in the gas phase for temperatures ranging between 102.4 and 184.6°C. The reaction is apparently homogeneous and obeys the first order rate law, yielding the following Arrhenius relationship:

Excess ethylene was added to the starting material in order to avoid complications from the backreaction. The cyclic 4‐center nature of the transition state proposed earlier has been unequivocally demonstrated by deuterium labelling. Mass‐spectral analyses show that the isobutene formed contains no deuterium. The hydrolyses products of the mixed trialkylaluminum formed during the reaction consist of monodeuteroethane and 2‐d1‐isobutane. The observed negative entropy of activation of ∼12 cal/°‐mole agrees with prediction and implies a reasonably tight transition state structure. Combined with the corresponding data for the non deuterized Al(i‐bu)3 reported earlier, these data result in a primary kinetic deuterium isotope effect of kH/kD = 1.3 × 100.6/θ corresponding to a ratio of the isotopic rate constants of 3.7 at 25°C. This result is in excellent agreement with a predicted value of 1.4 × 100.7/θ and it is in line with literature data on similar reactions involving cyclic transition state complexes.
Chemical kinetics of hydrogen halide lasers. 1. The H2Cl2 system
Authors: Cohen N. , Jacobs T. A. , Emanuel G. , Wilkins R. L. 
Published: January 2005

AbstractA detailed kinetic model of the HCl chemical laser produced by the flash photolytically initiated H2Cl2 explosion is described, and the results of computer calculations on such a system are discussed. It is shown that currently accepted values of the various rate constants, supplemented in a few cases by reasonable estimates of previously unmeasured rate constants, are adequate to approximate the observed laser behavior of this system. It is also shown that the chemistry of such a system is extremely complex, and exhibits a high degree of coupling between one reaction and another; therefore, great care is required to extract kinetic data from the optical behavior of such laser systems. It is further argued that different hydrogen halide lasers may behave quite differently from each other, depending on the relative magnitudes of the various rate constants involved.
Semi‐empirical potential energy surfaces for hydrogen‐atom transfer reactions
Authors: Salomon Mark 
Published: January 2005

AbstractA method for constructing potential energy surfaces previously proposed by the author has been extended to hydrogen transfer reactions between halide, oxygen, and carbon atoms. A qualitative relation was found between the repulsive energy and the number of anti‐bonding electrons. In general, the calculated kinetic isotope effect is in satisfactory agreement with observed values and the contributions by H‐atom tunneling to the rate of reaction is smaller than that obtained from other surfaces.
The Kinetics of the gas‐phase isomerization of 1,trans‐3,trans‐5‐heptatriene into the cis‐5‐isomer catalyzed by Nitric Oxide and the stabilization energy in the pentadienyl radical
Authors: Egger Kurt W. , Jola M. 
Published: January 2005

AbstractThe kinetics of the nitric oxide catalyzed, homogeneous, gas‐phase isomerization of 1,trans‐3,trans‐5‐heptatriene have been studied for temperatures ranging between 130°C and 241°C. The very clean reaction involves exclusive geometrical isomerization about the 5,6‐π‐bond. The observed rate constants for \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm NO} + trans - {\rm 3,}trans{\rm - 5}\stackrel{1}{\rightarrow}trans - 3,cis - 5 + {\rm NO} $\end{document} can be represented (with standard errors) by log k1 = (7.18 ± 0.06) – (16.75 ± 0.12)/θ, where θ = 2.303 RT in kcal/mole. The consecutive‐step reaction mechanism involves addition of NO to the double bond (Ka, b = ka/kb), followed by rotation of the 5,6‐CC bond in the adduct radical (kc.)Analysis of the observed activation parameters shows, that kc is rate‐controlling and consequently k1 = kcKa, b. Estimates of kc and Ka, b lead to a value of k1 in good agreement with experiment.Comparing our data with those previously obtained for the similar 1,3‐pentadiene system results in a value for the extra stabilization energy generated in the 1,3‐heptadienyl radical of 18.5 ± 1.7 kcal/mole. This value is discussed in view of comparable data in the literature.
The reactions of CF3 radicals with cyclanes and the determination of CH bond dissociation energies in cyclanes
Authors: Jones S. H. , Whittle E. 
Published: January 2005

AbstractThe reactions of CF3 radicals with the C3 to C7 cyclanes and spiropentane were studied and the following Arrhenius parameters were obtained for the reaction CF3 + c‐RH → CF3H + c‐R:

c‐RH
log A (cm3mole−1sec−1)
E (kcal/mole)
D(c‐R—H) (kcal/mole)

Cyclopropane
11.54
8.73
100.7

Cyclobutane
11.66
6.48
95.7

Cyclopentane
12.30
6.18
94.3

Cyclohexane
12.12
6.26
94.9

Cycloheptane
12.43
5.89
94.0

Spiropentane
11.91
8.12
98.8

The CF3 radicals were generated by photolysis of hexafluoroacetone or CF3I and a comparison is made of the utility of the two compounds as radical sources. The Arrhenius parameters are compared with those for corresponding reactions of CH3 radicals with cyclanes, and the general reactivity of cyclic compounds toward free radicals is discussed. An Evans‐Polanyi treatment is used to derive CH bond dissociation energies in cyclanes; and these results, based on the reactions of CF3 with cyclanes, agree well with those previously obtained using CH3 plus cyclanes. The final mean values are shown above.
Computer simulation of cage processes and some difficulties with present models
Authors: Walling Cheves , Lepley Arthur R. 
Published: January 2005

AbstractA simple model involving random displacements of particles in a cubic lattice is used to evaluate the importance of primary and secondary recombination in cage processes and leads to estimates of the lifetime of cage pehnomena. However, it is pointed out that all such models, and treatments which attempt to relate processes at the molecular level with bulk viscosity or diffusion constants, are inherently qualitative since they ignore the important correlation between motions of neighboring molecules.
Rotating sector study of the gas phase photolysis of the carbon tetrachloride–cyclohexane system
Authors: White Merle L. , Kuntz Robert R. 
Published: January 2005

AbstractThe rate constant for the combination of trichloromethyl radicals in the gas phase has been measured by applying the rotating sector technique to the gas phase carbon tetrachloride–cyclohexane photochemical system. A temperature‐independent rate constant, k5, of 3.9 ± 1.0 × 1012 cc mole−1 sec−1 was found. Arrhenius parameters for the reaction

were found to be given by the expression log k4 = 11.79 – (10,700/2.3 RT).
The addition of methyl radicals to hexafluoropropylene
Authors: Thynne J. C. J. 
Published: January 2005

AbstractThe addition of methyl radicals to hexafluoropropylene has been studied over the temperature range 81°–203°C using a mass‐balance technique involving the photolysis of biacetyl in the presence of hexafluoropropylene–isobutane mixtures. For the reaction

the rate constant is given by the equation

The result suggests that methyl radicals are very unselective in their behavior reacting with tetrafluoroethylene and hexafluoropropylene at similar rates. This is in marked contrast to the behavior of oxygen atoms with these olefins.
The arrhenius factors for some six‐center unimolecular reactions
Authors: Blades A. T. , Sandhu H. S. 
Published: January 2005

AbstractThe Pyrolysis of ethyl formate has been carried out in the temperature range 557°–630° and the rate expression k = 1012.34 e−48,100±500/RT sec−1 was obtained, in agreement with the prediction of O'Neal and Benson [1]. Calculated Arrhenius A‐factors and experimental rate constants have been used to obtain the activation energies for the decomposition of the following compounds by the six‐center molecular mechanism (in kcal/mole): 2‐pentanone 59; methoxyacetone, 58; 2,4‐pentanedione, 51; methyl butyrate, ≥ 70; 1‐heptene, 54, and 4‐methyl‐1‐hexene, 54–55.
The photolysis of N2O at 1470 Å
Authors: Dodge Marcia C. , Heicklen Julian 
Published: January 2005

AbstractThe photolysis of pure N2O, N2O and N2, and N2O and C3H6 mixtures at 1470 Å and room temperature has been studied to determine the relative importance of the primary processes. The results are
equation image
where ϕ{O(1D)} = 0.515 represents both the O(1D) produced in the primary act and that produced by collisional quenching of O(1S); ϕ{N2(3Σ)} = 0.084 represents only that portion of N2(3ϕ) which dissociates N2O on deactivation; and ϕ{O(1S)} = 0.38 – ±{N(2D)} represents only that portion of O(1S) which enters into chemical reaction with N2O. If the reaction of O(1S) with N2O yields only N2 and O2 as products, which seems likely from potential‐energy curve considerations then ±{O(1S)} = 0.135 ± 0.06 and ϕ{N(2D)} = 0.245 ± 0.06. Young and coworkers [4] have found from spectroscopic observations that the total quantum yield of O(1S) is about 0.5. Thus it can be concluded that collisional removal of O(1S) by N2O yields mainly O(1D) with chemical reaction being less important. Furthermore, most of the O(1D) is produced this way, and the true primary yield of O(1D) is about 0.15. The metastable N(2D) is not deactivated by N2O, but is removed by chemical reaction to produce N2 and NO. The results further indicate that N2(3Σ) dissociates N2O at least 80% of the time during quenching. The relative efficiency of N2O compared to N2 is about 2 for the removal of O(1D). O(1S) is removed about 90 times as efficiently by C3H6 as by N2O.
Some hydrogen abstraction reactions of the trichloromethyl radical
Authors: Wampler Fred B. , Kuntz Robert R. 
Published: January 2005

AbstractThe gas phase photolysis of CCl4 in the presence of several alkanes has been used to obtain Arrhenius parameters for the abstraction of hydrogen atoms by the CCl3 radical: magnified image The following log k4 values were obtained:

RH
log k4

c‐C5H10,

n‐C6H14

2,3‐Dimethylbutane

c‐C7H14

Methylcyclohexane

c‐C8H16

The results are compared to those for CH3 and CF3 radicals.
The reactions of CF3 and CD3 radicals with boron trimethyl
Authors: Bell T. N. , Platt A. E. 
Published: January 2005

AbstractHydrogen abstraction from boron trimethyl has been studied using the abstracting radicals CF3 and CD3, from the photolysis of the corresponding ketones over the temperature range of 150° to 300°C. The following Arrhenius parameters were obtained:

The difference E – E in the case of BMe3 is considered due, in part, to polar effects. An exchange reaction is proposed for both CF3 and CD3 in collisions with BMe3:

Radical combination of CF3 and CH2BMe2 leads to a hot molecule which undergoes a β‐fluoro rearrangement elimination process, or a stabilized molecule which can thermally decompose: magnified image
Multistage reactions, equilibrium, and detailed balancing: A linear algebra approach
Authors: Lee J. 
Published: January 2005

AbstractMethods of linear algebra are applied to (a) the problem of determining whether detailed balancing for some or all stages of a chemical process is implicit from the existence of steady state for some or all of the chemical species involved, and (b) the formulation of general concentration‐type equilibrium relationships solely from kinetic considerations and the assumption of full detailed balancing.
Disproportionation‐combination ratios of large branched alkyl radicals
Authors: Georgakakos J. H. , Rabinovitch B. S. , Larson C. W. 
Published: January 2005

AbstractThe disproportionation‐combination reactions of radicals 4,4‐dimethylpentyl‐2 and 2,4‐dimethylpentyl‐2, produced by collisional stabilization of the respective chemically activated species, have been studied at 298°K, with and without getter radicals. Use of getters t‐C4H9 and C2H5 with 4,4‐dimethylpentyl‐2, and of iso‐C3H7 with 2,4‐dimethylpentyl‐2 yielded disproportionation‐combination ratios ω for parent‐getter and t‐C4H9‐C2H5 cross reactions, and for the mutual reaction of t‐C4H9 radicals. The unstabilized hot radicals decompose, and these experiments also yielded values for the high‐pressure rate constant ka∞ of 1.70 × 108sec–1 and 2.11 × 107sec–1 for 4,4‐dimethylpentyl‐2 and 2,4‐dimethylpentyl‐2, respectively. The results, compared to those for other large alkyl radical systems obtained earlier, suggest that steric effects influence the accessibility of H atoms for transfer.
The decomposition of chemically activated n–butane, isopentane, neohexane, and n–pentane and the correlation of their decomposition rates with radical recombination rates.
Authors: Hase W. L. , Johnson R. L. , Simons J. W. 
Published: January 2005

AbstractThe total decomposition rates of the chemically activated alkanes n‐butane, n‐pentane, isopentane, and neohexane were measured using an internal comparison technique. Chemical activation was by the CH insertion reaction of excited singlet‐state methylene radicals. A total of ten rate constants ranging from 4.6 × 105 to 2.3 × 107 sec−1 were measured for these alkanes at different excitation energies. These rates correlate via RRKM theory calculations with thermal A‐factors in the range of 1016.1 to 1017.1 sec−1 for free rotoractivated complex models and in the range of 1016.4 to 1017.8 sec−1 for vibrator‐activated complex models. It was found that high critical energies for decomposition, “tight” radical models, and activated complex models with free internal rotations were required to correlate the decomposition rates of these alkanes with estimated alkyl radical recombination rates. The correlation is just barely possible even for these favorable extremes, indicating that there may be a basic discrepancy between the recombination rate and decomposition rate data for alkanes.
The pyrolyses of tri‐ and tetramethylethylene in the presence of nitric oxide
Authors: Schuchmann H.‐P. , Laidler K. J. 
Published: January 2005

AbstractThe pyrolyses of trimethylethylene and tetramethylethylene have been investigated in the presence and absence of nitric oxide. It appears that apart from a unimolecular split, e.g.,
magnified image
a disproportionation reaction such as
magnified image
may play an important role in initiation. Nitric oxide had no effect on H2 production, which is probably a molecular process. There was similar behavior of both compounds in the presence of NO, indicating that the olefinic hydrogen atom does not play a decisive role. Other aspects of the mechanisms are discussed.
Kinetics of the formation of cyclobutane from ethylene
Authors: Quick L. M. , Knecht D. A. , Back M. H. 
Published: January 2005

AbstractThe rate of the thermal reaction of ethylene to form cyclobutane has been measured over the temperature range 723°–786°K and at pressures between 300 and 1300 torr. The equilibrium constant for the system
\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$${\rm 2C}_{\rm 2} {\rm H}_{\rm 4}\mathop {\leftrightharpoons}\limits_{kf}^{kr} c - {\rm C}_{\rm 4} {\rm H}_{\rm 8}$$\end{document}
was calculated both from the initial rate data and from measurements of the equilibrium concentration of cyclobutane. Agreement with the reported thermodynamic quantities for cyclobutane was satisfactory. The initial rate data gave the following epxression for kf:

while the measurements of the equilibrium concentration of cyclobutane gave the expression for K,

.
A flash photolysis–resonance fluorescence kinetics study of ground‐state sulfur atoms. II. Rate parameters for reaction of S(3P) with C2H4
Authors: Davis D. D. , Klemm R. B. , Braun W. , Pilling M. 
Published: January 2005

AbstractAbsolute rate constants for the reaction of S(3P) with ethylene were measured over an ethylene concentration range of 7, a total pressure of 50 to 400 torr, and a flash intensity range of 10. At 298°K, the bimolecular rate constant was found to be invariant over this range of variables and had a measured value of 4.96 × 10−13 cm3 molec−1 s−1. Over the temperature range of 218° to 442°K, the rate data could be fit to a simple Arrhenius equation of the form

Units are cm3 molec−1 s−1. The dependence of the measured value of k1 on the concentration of the reaction product ethylene episulfide is discussed.
Kinetics of the metathetical reaction between carbon tetrachloride and toluene
Authors: Shoulders Diana Curcio , Hardwick T. J. , Ketter Donald C. , Pukanic George W. 
Published: January 2005

AbstractA metathetical reaction between carbon tetrachloride and toluene to give benzyl chloride and chloroform occurs at temperatures above 200°C (k = 4.8 × 1010 e−32,900/RT cc mole−1sec−1). The reaction does not involve free radicals, as is shown by the kinetic behavior of the system, by the lack of effect of added free‐radical chain inhibitors, and by the absence of the expected chain termination product, hexachloroethane. The reaction is one of a general type between carbon tetrachloride and alkanes or alkylaromatics, but at the temperatures required it is often obscured by dehydrohalogenation of the product to the highly reactive olefin. At high temperatures, benzyl chloride reacts with toluene to give bibenzyl and hydrogen chloride, apparently also by a metathetical reaction. The transition state is postulated to be four‐center, in which the carbon‐chlorine and carbon–hydrogen bonds are broken and reformed: The experimental preexponential factor is in good agreement with that calculated from transition‐state theory.
The photolysis of N2O at 2139 Å and 1849 Å
Authors: Simonaitis R. , Greenberg Raymond I. , Heicklen Julian 
Published: January 2005

AbstractThe method of chemical difference was utilized to accurately determine the relative importance of all the reaction steps in the direct photolysis of N2O at 2139 Å (25° and 250°C) and 1849 Å (25° C), as well as in the Hg6(1P1)‐sensitized photolysis of N2O at 1849 Å (25°C). In all cases, the primary process is predominantly, if not exclusively,Experiments with trace amounts of C3H6added showed a slight, but not significant, difference in product ratios (N2and O2). From these experiments the quantum yield of O(3P) from all possible sources was estimated as 0.02 ± 0.02. Experiments with excess N2at 1849 Å indicated that O(1S) was not produced in the direct photolysis. The O(1S) yield is probably zero, and certainly <0.05. The O(1D) atom can react with N2O viaThe ratiok2/k3was found to be 0.69 ± 0.05 in all cases. When combined with other data from our laboratory, the average value is 0.65 ± 0.07. This represents the value for translationally energetic O(1D) atoms. When excess He was added to remove the excess translational energy,k2/k3rose to 0.83 ± 0.06, which is in reasonable agreement with the value of 1.01 ± 0.06 found in another laboratory. We conclude that for O(1D) atoms with no excess thermal energy,k2/k3= 0.90 ± 0.10.
Decay kinetics of the triplet and anthrasemiquinone radicals in aqueous organic media
Authors: Kuzmin V. A. , Chibisov A. K. , Karyakin A. V. 
Published: January 2005

AbstractElectron transfer involving triplet molecules of anthraquinone sulfonates has been studied by flash photolysis. It was revealed that semiquinone radicals were formed in one‐electron oxidation of carbonate anions. Absorption spectra and the kinetics of decay transients in aqueous and aqueous‐alcoholic solutions have been studied.
The alpha effect. A review
Authors: Fina Nick J. , Edwards John O. 
Published: January 2005

AbstractInstances of high reactivity (as signaled by a positive Brönsted deviation) by nucleophiles bearing one or more unshared pairs of electrons on an atom adjacent to the nucleophilic center (the alpha effect) are surveyed in the context of possible explanations for this phenomenon. No single cause appears to account satisfactorily for all the data. However, four factors (ground‐state destabilization of the nucleophile, transition‐state stabilization, solvent effect differences for alpha and nonalpha nucleophiles, and product stability) may be involved in contributory roles. The response to proton basicity of a substrate is probably not related to its susceptibility to the alpha effect. Carbon electrophiles seem to be receptive to the alpha effect in the order digonal > trigonal > tetrahedral. The inconsistent behavior of alpha nucleophiles makes the prediction of alpha effects rather risky and confirms the complicated nature of nucleophilic substitutions.
Very low‐pressure pyrolysis. VIII. The decomposition of Di‐t‐amyl peroxide
Authors: Perona M. J. , Golden D. M. 
Published: January 2005

AbstractThe very low‐pressure pyrolysis (VLPP) technique has been applied to the pyrolysis of di‐t‐amyl peroxide (DTAP) over the temperature range 523‐633°K. VLPP yields a low‐pressure rate constant, kuni The conversion of kuni to k∞ which must be made to calculate the Arrhenius parameters, is accomplished via the RRKM theory. The transition state model used in the RRKM calculations was based on a transition state model which accurately reproduced the VLPP data for di‐t‐butyl peroxide for which the Arrhenius parameters are well known. For the decomposition of DTAP it was found that log k∞(300°K) = 15.8 ‐ 36.4/θ, where θ = 2.303RT, in kcal/mole, and the units of k∞, are sec−1.
Kinetics of chemically activated ethane
Authors: Growcock F. B. , Hase W. L. , Simons J. W. 
Published: January 2005

AbstractChemically activated ethane, with an excitation energy of 114.9 ± 2 kcal/mole, was formed by reaction with methane of excited singlet methylene radicals produced by the 4358 Å photolysis of diazomethane. A decomposition rate constant of (4.6 ± 1.2) × 109 sec−1 was measured for the chemically activated ethane. This result agrees, via RRKM theory, with most other chemically activated ethane data, and the result predicts, via RRKM and absolute rate theory for E0 = 85.8 kcal/mole, E* = 114.9 kcal/mole, and kE = 4.6 × 101 sec−1, a thermal A‐factor at 600°K of 1016.6±0.2 sec−1, in approximate agreement with the more recent experimental values. Combining 2 kcal/mole uncertainties in E0 and E* with the uncertainty in our rate constant yields an A‐factor range of 1016.6±0.7 sec−1. It is emphasized that this large uncertainty in the A‐factor results from an improbable combination of uncertainty limits for the various parameters. These decomposition results predict, via absolute rate theory (with E0(recombination) = 0) and statistical thermodynamic equilibrium constants, methyl radical recombination rates at 25°C of between 4.4 × 108 to 3.1 × 109 l.‐mole−1‐sec−1, which are 60 to 8 times lower, respectively, than the apparently quite reliable experimental value. A value of E0(recombination) greater than zero offers no improvement, and a value less than zero would be quite unusual. Activated complexes consistent with the experimental recombination rate and E0(recombination) = 0 greatly overestimate the experimental chemical activation and high pressure thermal decomposition rate data. Absolute rate theory as it is applied here in a straightforward way has failed in this case, or a significant amount of internally consistent data are in serious error. Some corrections to our previous calculations for higher alkanes are discussed in Appendix II.