bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relative rate constants for the reactions of trichloropropenyl radical. Application of the two‐parameter Taft equation
Authors: Afanas'ev I. B. , Baranova N. G. , Samokhvalov G. I. 
Published: January 2005

AbstractThe relative rate constants for the hydrogen atom abstraction by CCl3CHCH· radical from CH2Cl2, CHCl3, CH3COCH3, CH3CN, C6H5CH3, C6H5OCH3, CH3CHO, and CH3OH in the liquid phase at 20°C have been measured. It was shown that these reaction rate constants are correlated by the two‐parameter Taft equation with ρ* = 0.726 ± 0.096, r* = 1.22 ± 0.16. A relationship between r* and bond dissociation energy D(RH) has been found for the abstraction reactions of different free radicals.
Laser‐powered homogeneous pyrolysis
Authors: Shaub W. M. , Bauer S. H. 
Published: January 2005

AbstractThe large absorption cross sections for infrared radiation possessed by a few rather stable molecular species, their relatively fast vibration–translation relaxation times, and the availability of large laser fluxes at their characteristic frequencies have been effectively exploited to generate high bath temperatures for gas‐phase reactions under strictly homogeneous conditions. Controlled temperatures from 500 to 1500°K have been developed with a modest CO2 laser. Rise times for heating are estimated to be in the millisecond range, with reaction times ≈ 10 seconds. Operating pressures [reagents, radiation absorber (generally SF6), and diluent] range from 10 to 100 torr. Thus laser‐powered homogeneous pyrolysis (LPHP) is complementary to the single‐pulse shock‐tube technique [rise time ∼10−8 sec; reaction time ∼10−3 sec] for obtaining product distributions in gas‐phase pyrolyses, and for measuring relative rates in the absence of hot walls. The latter may (and generally do) introduce catalytic effects. Further, LPHP is very simple and ideally suited for exploratory investigations of small amounts of reagent (≈10−6 mole); also, sample cells may be heated externally to augment the vapor pressure of slightly volatile reagents. Conventional analytical procedures (gas chromatography, mass spectrometry) were used to follow the course of pyrolysis.The primary chemical kinetic parameters, the temperature and density of the reactants, have both spatial and temporal distributions. Computer programs were developed for estimating T(r,x;t), given the radial intensity distributon in the incident beam, the absorption coefficient of the SF6 (as a function of density and temperature) for the irradiating line, as well as the mean heat capacity and thermal conductivity of the gas mixture. However, the computed profiles did not prove useful since the effects of convection, which could not be included in the calculations, perturb the initial distribution significantly within a few milliseconds. Indeed, it proved practical to enhance convection so as to homogenize the cell composition. When the incident radiation was chopped, frequencies ranging from 100 Hz to 1 Hz gave the same product distributions. A practical procedure is to use a “chemical thermometer” to establish a mean effective temperature for a given experimental configuration. Examples showing how to measure relative rate constants for molecular conversions, and the use of LPHP for qualitative determinations of product distributions as a function of temperature are presented. Finally, a number of high‐temperature conversions are described to illustrate the utility of LPHP for flash thermolysis.
The oxidation of hydrocarbons by water vapor behind high‐temperature shock‐waves
Authors: Shaviv A. , Bar‐Nun A. 
Published: January 2005

AbstractThe oxidation of acetylene by water vapor was studied behind the reflected shock in a single‐pulse shock tube. Computer simulation experiments reproduced the experimental results in the temperature range of 1500 to 2000°K. The kinetic scheme suggested here involves three major processes, (1) production of hydrogen atoms by the sequence of reactions which lead from acetylene to carbon; (2) production of OH radicals, mainly by the reaction H + H2O → H2 + OH, and (3) fast oxidation of the acetylene and other C/H species by the available oxidants in the system. The experimental results of methane oxidation suggest that methane is converted to acetylene prior to its oxidation. The implication of the experimental results to processes occurring in planetary atmospheres as a result of thunder shock waves is briefly discussed.
Kinetic and product distribution analysis for competitive recombination reactions
Authors: Ehrenson S. 
Published: January 2005

AbstractExact solution methods are developed for the complex kinetic and product distribution equations encountered in a particular type of competitive recombination or crossover reaction involving “cages.” Pertinent reaction systems are those where scavenging of the intermediates escaping the cages is restricted to species similar to these intermediates, thereby limiting potentially undesired side effects of the scavenger. The trustworthiness of the reaction constants which may be obtained, particularly the fraction of recombination occurring within the cage, are analyzed in terms of sources of possible error. Several extensions of the method are briefly discussed, such as in distinctions between inter‐ and intramolecular rearrangements. Full detailing of the solution methods should facilitate their use in the analysis of similar reaction schemes.
Chemically activated methylcyclobutane exothermicity of singlet methylene reactions and the heat of formation of singlet methylene
Authors: Simons J. W. , Hase W. L. , Phillips R. J. , Porter E. J. , Growcock F. B. 
Published: January 2005

AbstractThe specific decomposition rates of chemically activated methylcyclobutane produced from CH2(1A1) reaction with cyclobutane have been determined. CH2(1A1)was produced from ketene photolyses at 3340 and 3130 Å and from diazomethane photolyses at 4358 and 3660 Å. Comparisons of the excitation energies of the methylcyclobutane, determined by RRKM theory calculations, and the experimental results for the ketene systems, with thermochemically predicted maximum excitation energies, favor an Arrhenius A factor in the range of 5 × 1015 to 1 × 1016 sec−1 for methylcyclobutane. This result is consistent with (1) the comparison of RRKM theory calculations and the experimental unimolecular falloff for methylcyclobutane, (2) the comparison of experimental A factors for cyclobutane and other alkylcyclobutane decompositions, and (3) two out of three reported experimental A factors for methylcyclobutane. An analysis of these and previous results leads to a value of the CH2(1A1) ↔ CH2(3B1) energy splitting of 9±3 kcal/mole.
Mathematical simulation of the oxygen–ethane reaction
Authors: Kulich Donald M. , Taylor Jay E. 
Published: January 2005

AbstractPrevious experimentation on the initial stages of the oxygen‐ethane reaction at temperatures near 600°C demonstrated the existence of a significant induction period under homogeneous conditions. Below 0.13% conversion, the rate with oxygen is less than the rate of ethane pyrolysis in the absence of oxygen. Experiments were conducted with mixtures of ∼1% ethane and ∼0.4% oxygen in nitrogen using the “wall‐less” technique. Mathematical simulations of the oxidative and simple pyrolyses of ethane were established by a numerical analysis. The experimentally observed induction period and the mechanisms previously proposed are supported by these computations. Steady‐state conditions are much more slowly attained in the presence of oxygen than in its absence.
Liquid phase kinetic study of the formation and decomposition of methylsulfonyl and cyclohexylsulfonyl radicals in the cyclohexane–MeSO2C1‐SO2 System at 150°
Authors: Horowitz Abraham 
Published: January 2005

AbstractThe thermally and radiolytically induced chain decomposition of methanesulfonyl chloride (MeSO2Cl) in liquid cyclohexane (RH) was studied at 150°C. The main products, chlorocyclohexane, sulfur dioxide, and methane, are formed in almost equal yields, and a relatively small amount of methyl chloride is also observed. The formation and addition of SO2 strongly inhibit the chain decomposition reaction. By kinetic analysis it is shown that the formation of the main products can be explained only in terms of a mechanism that postulates the decomposition of MeSO2, and that the alternative mechanism of methane and SO2 formation via the methanesulfinic acid is inconsistent with the kinetic behavior of the system. For the reactions Me + MeSO2Cl → MeCl + MeSO2(2b), Me + RH → MeH + R (4), and Me + CCl4 → MeCCl4 → MeCl + CCl3 (15b) the following rate constant ratios are determined; k2b/k4=2.17±0.20 and k2b/k15b=2.63±0.52. For the reactions R + MeSO2Cl → RCl + MeSO2(2a) and R + CCl4 → RCl + CCl3 (15a), k2a/k15a is equal to 1.55±0.05. In addition the equilibrium constant K7 for the reaction R + SO2 ⇄ RSO2 (7) is estimated as being equal to (9.4±3) × 103 mole/l.
A comparison of two‐dimensional and three‐dimensional trajectory calculations in thermal HBr2 and H2Br systems
Authors: Pace S. A. , White J. M. 
Published: January 2005

AbstractTwo‐dimensional (2D) and three‐dimensional (3D) quasiclassical trajectory calculations on H + Br2 at 300°K and H + HBr at 1000°K are reported. Angular scattering, energy disposal, and impact parameter distributions for reactive collisions are compared after removal of phase‐space factors (dimensionality bias) as a means of examining the similarities and differences in the dynamic bias in 2D and 3D. Qualitatively, for all reactive processes studied, the 3D trajectory calculated distributions are reproduced by the phase‐space adjusted 2D trajectory data. Thus the surprisal of these angular scattering, energy disposal, and impact parameter distributions is dimensionally invariant, and the same dynamic bias appears in 2D and 3D. A systematic method for converting 2D reaction probabilities and maximum reactive impact parameters into 3D rate coefficients is presented. We find that trajectory calculated 3D rate coefficients may in general differ markedly from those derived from 2D trajectory data. In particular, the surprisal associated with rate coefficients depends on dimensionality for the H + HBr → H2 + Br reaction, but is invariant for the H′ + HBr → H′Br + Br and H + Br2 → HBr + Br reactions.
The gas phase pyrolysis of alkyl nitrites. I. t‐butyl nitrite
Authors: Batt L. , Milne R. T. 
Published: January 2005

AbstractThe rate of decomposition of t‐butyl nitrite (TBN) has been studied in a static system over the temperature range of 120–160°C. For low concentrations of TBN (10−5‐ 10−4M), but with a high total pressure of CF4 (∼0.9 atm) and small extents of reaction (∼1%), the first‐order homogeneous rates of acetone (M2K) formation are a direct measure of reaction (1), since k3» k2 (NO): TBN . Addition of large amounts of NO in place of CF4 almost completely suppresses M2K formation. This shows that reaction (1) is the only route for this product. The rate of reaction (1) is given by k1 = 1016.3–40.3/θ s−1. Since (E1 + RT) and ΔH are identical, both may be equated with D(RO‐NO) = 40.9 ± 0.8 kcal/mole and E2 = O ± 1 kcal/mole. From ΔS and A1, k2 is calculated to be 1010.4M−1 ·s−1, implying that combination of tBuO and NO occurs once every ten collisions. From an independent observation that k2/k2′ = 1.7 ± 0.25 independent of temperature, it is concluded that k2′ = 1010.2M−1 · s−1 and k1′ = 1015.9−40.2/θ s−1;
equation image
. This study shows that MeNO arises solely as a result of the combination of Me and NO. Since NO is such an excellent radical trap for t‐Bu\documentclass{article}\pagestyle{empty}\begin{document}${\rm Me\dot O}$\end{document}, reaction (2) may be used in a competitive study of the decomposition of tBu\documentclass{article}\pagestyle{empty}\begin{document}${\rm Me\dot O}$\end{document} in order to obtain the first absolute value for k3. Preliminary results show that k3 (∞) = 1015.7–17.0/θ s−1. The pressure dependence of k3 is demonstrated over the range of 10−2−1 atm (160°C). The thermochemistry for reaction (3) implies that the Hg 6(3P1) sensitised decomposition of t‐BuOH occurs via reaction (m):
equation image
In addition to the products accounted for by the TBN radical split, isobutene is formed as a result of the 6‐centre elimination of HONO: TBN \documentclass{article}\pagestyle{empty}\begin{document}$\mathop \to \limits^7 $\end{document} isobutene + HONO. The rate of formation of isobutene is given by k7 = 1012.9–33.6/θ s−1. t‐BuOH, formed at a rate comparable to that of isobutene–at least in the initial stages–is thought to arise as a result of secondary reactions between TBN and HONO. The apparent discrepancy between this and previous studies is reconciled in terms of the above parallel reactions (1) and (7), such that k + 2k7 = 1014.7–36.2/θ s−1.
The reaction of OH with CO
Authors: Sie B. K. T. , Simonaitis R. , Heicklen J. 
Published: January 2005

AbstractHydroxyl radicals were prepared from the photolysis of N2O at 213.9 nm in the presence of excess H2. The O(1D) produced in the primary photolytic act reacts with H2 to produce OH radicals. If CO is also present, then OH can react either with H2 or CO:

equation image

The competition between reactions (1) and (2) was measured by measuring the CO2 yield at various values of the ratio [CO]/[H2] at 217–298°K. At 298°K the ratio of the rate coefficients k1/k2 increased with pressure from a low‐pressure limiting value of 14 to a high‐pressure limiting value of 50. The low‐pressure limiting value agrees well with the low‐pressure values found by others. At lower temperatures our high‐pressure values of k1/k2 were larger than deduced from the accepted low‐pressure Arrhenius expression and could be fitted to the expression

The mechanism which seems to fit the results best is
equation image
with k1° = kakb/k‐a and k1∞ = ka.
Reactions of methyl radicals with acetaldehyde and acetaldehyde‐d1. II. BEBO calculations of the temperature dependence of the rate constants
Authors: BéRces T. , MáRta F. 
Published: January 2005

AbstractThe BEBO method was used to calculate the kinetic isotope effect for formyl‐hydrogen abstraction from acetaldehyde by methyl radicals. The calculated isotope effect and experimental ratios of the rate constants obtained at 785°K for the reactions of CH3 with CH3CHO and CH3CDO, together with the theoretical temperature dependence of the specific rates (as formulated by the BEBO theory), were used to obtain rate constants for the steps CH3 + CH3CHO → CH4 + CH3CO (2a), CH3 + CH3CHO → CH4 + CH2CHO (2b), and CH3 + CH3CDO → CH3D + CH3CO (1a) between 298 and 1224°K.It was shown that the curvature apparent in the Arrhenius plot of the rate coefficient k2 reported for the reaction of methyl radicals with acetaldehyde in the temperature range of 298–1224°K is caused both by the simultaneous contribution of steps (2a) and (2b) to methane formation, and by the curvature in the Arrhenius plots of the two elementary rate constants themselves. The predicted curve agrees well with the experimental data, especially if the tunneling correction is applied.
The SO2(3B1) photosensitized isomerization of cis‐ and trans‐1,2‐difluoroethylene
Authors: Wampler Fred B. 
Published: January 2005

AbstractQuantum yield measurements for the SO2(3B1) photosensitized isomerization of cis‐1,2‐difluoroethylene have been made at 3712 Å and 22°C. The [SO2]/[cis‐C2F2H2] ratio was varied from 47.4 to 455 and the quantum yield measurements over this variation of concentration ratios were consistent with a mechanism in which SO2(3B1) molecules and the cis isomer form a collision intermediate which decomposes with a probability of 0.42 ± 0.17 and 0.58 ± 0.17 of producing trans‐ and cis‐1,2‐difluoroethylene, respectively. When SO2 was subjected to prolonged irradiations in the presence of initially either pure cis‐ or pure trans‐1,2‐difluoroethylene, a photostationary composition, [cis]/[trans] = 1.0 ± 0.2, was obtained. The rate constant at 22°C for removal of SO2(3B1) molecules by cis‐1,2‐difluoroethylene was estimated to be (1.72 ± 0.72) × 1010 1./mole · sec.
Triplet excited states of nitronaphthalenes. III. 1,4‐dinitronaphthalene
Authors: Capellos C. , Suryanarayanan K. 
Published: January 2005

AbstractNanosecond flash photolysis of 1,4‐dinitronaphthalene (1,4‐DNO2N) in aerated and deaerated solvents shows a transient species with absorption maximum at 545 nm. The maximum of the transient absorption is independent of solvent polarity and its lifetime seems to be a function of the hydrogen donor efficiency of the solvent. The transient absorption is attributed to the lowest excited triplet state of 1,4‐DNO2N. The reactivity of this state for hydrogen abstraction from tributyl tin hydride (Bu3SnH), Kq = 3.8 × 108M−1 sec, is almost equal to that of nitrobezene triplet state which has been characterized as an n → π* state. Based on spectroscopic and kinetic evidence obtained in the present work, the triplet state of 1,4‐DNO2N behaves as an n → π* state in nonpolar solvents, while in polar solvents the state is predominantly n → π* with a small amount of intramolecular charge transfer character.
Analysis of nonlinear reactions in modulated molecular beam surface experiments
Authors: Olander D. R. , Ullman Alan 
Published: January 2005

AbstractAn approximate method of analyzing nonlinear reaction models in modulated molecular beam surface kinetic studies is developed. The exact method for treating nonlinear surface mechanisms is tedious and almost always requires computer analysis. The proposed approximate method is a simple extension of the Fourier expansion technique valid for linear surface reactions; it quickly provides analytical expressions for the phase lag and amplitude of the reaction product for any type of nonlinear surface mechanism, which greatly facilitates comparison of theory and experiment. The approximate and exact methods are compared for a number of prototypical adsorption–desorption reactions which include coverage‐dependent adsorption and desorption kinetics of order greater than unity. Except for certain extreme forms of coverage‐dependent adsorption, the approximate method provides a good representation of the exact solution. The errors increase as the nonlinearities become stronger. Fortunately, when the discrepancy between the two methods is substantial, the reaction product signal is so highly demodulated that reliable experimental data usually cannot be obtained in these regions anyway.
The mechanism of the reaction between hydroxyl ions and some internally hydrogen‐bonded acids
Authors: Perlmutter‐Hayman Berta , Sarfaty Rona , Shinar Ruth 
Published: January 2005

AbstractThe kinetics of the proton transfer between hydroxyl ions and phenylazoresorcinol, 4‐(p‐nitrophenylazo), and 4‐(m‐nitrophenylazo) resorcinol have been investigated at 25°C and an ionic strength of 0.1M, in a wider pH range than had been done by previous authors. The rate at first decreased with decreasing [OH−], reached a minimum, and then started to increase with decreasing [OH−]. This unusual effect is explained by a mechanism suggested earlier for tropaeolin O. Rate constants and equilibrium constants have been evaluated and discussed.The experimental data were obtained by the T‐jump method.
Reaction of atomic oxygen with cyclopentadiene
Authors: Nakamura Kazumoto , Koda Seiichiro 
Published: January 2005

AbstractThe reaction of 1,3‐cyclopentadiene (CPD) with ground‐state atomic oxygen O(3P), produced by mercury photosensitized decomposition of nitrous oxide, was studied. The identified products were carbon monoxide and the following C4H6 isomers: 3‐methylcyclopropene, 1,3‐butadiene, 1,2‐butadiene, and 1‐butyne. The yield of carbon monoxide over oxygen atoms produced (ϕCO) was equal to the sum of the yields of C4H6 isomers in any experiment. ϕCO was 0.43 at the total pressure of 6.5 torr and 0.20 at 500 torr. We did not succeed in detecting any addition products such as C5H6O isomers.It was found that 3‐methylcyclopropene was produced with excess energy and was partly isomerized to other C4H6 isomers, especially to 1‐butyne. The excess energy was estimated to be about 50 kcal/mol.The rate coefficient of the reaction was obtained relative to those for the reactions of atomic oxygen with trans‐2‐butene and 1‐butene. The ratios kCPD+O/ktrans‐2‐butene+O= 2.34 and kCPD+O/k1‐butene+O = 11.3 were obtained.Probable reaction mechanisms and intermediates are suggested.
The gas‐phase pyrolysis of alkyl nitrites. III. Isopropyl nitrite
Authors: Batt L. , Milne R. T. 
Published: January 2005

AbstractThe rate of decomposition of isopropyl nitrite (IPN) has been studied in a static system over the temperature range of 130–160°C. For low concentrations of IPN (1–5 × 10−5M), but with a high total pressure of CF4 (∼0.9 atm) and small extents of reaction (∼1%), the first‐order rates of acetaldehyde (AcH) formation are a direct measure of reaction (1), since k3 » k2(NO): \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$ {\rm IPN}\begin{array}{rcl} 1 \\ {\rightleftarrows} \\ 2 \\ \end{array}i - \Pr \mathop {\rm O}\limits^. + {\rm NO},i - \Pr \mathop {\rm O}\limits^. \stackrel{3}{\longrightarrow} {\rm AcH} + {\rm Me}. $\end{document} Addition of large amounts of NO (∼0.9 atm) in place of CF4 almost completely suppressed AcH formation. Addition of large amounts of isobutane – t‐BuH – (∼0.9 atm) in place of CF4 at 160°C resulted in decreasing the AcH by 25%. Thus 25% of \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^{\rm .} $\end{document} were trapped by the t‐BuH (4): \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^. + t - {\rm BuH} \stackrel{4}{\longrightarrow} i - \Pr {\rm OH} + (t - {\rm Bu}). $\end{document} The result of adding either NO or t‐BuH shows that reaction (1) is the only route for the production of AcH. The rate constant for reaction (1) is given by k1 = 1016.2±0.4–41.0±0.8/θ sec−1.Since (E1 + RT) and ΔH°1 are identical, within experimental error, both may be equated with D(i‐PrO‐NO) = 41.6 ± 0.8 kcal/mol and E2 = 0 ± 0.8 kcal/mol. The thermochemistry leads to the result that \documentclass{article}\pagestyle{empty}\begin{document}$ \Delta H_f^\circ (i - {\rm Pr}\mathop {\rm O}\limits^{\rm .} ) = - 11.9 \pm 0.8{\rm kcal}/{\rm mol}. $\end{document} From ΔS°1 and A1, k2 is calculated to be 1010.5±0.4M−1·sec−1. From an independent observation that k6/k2 = 0.19 ± 0.03 independent of temperature we find E6 = 0 ± 1 kcal/mol and k6 = 109.8+0.4M−;1·sec−1: \documentclass{article}\pagestyle{empty}\begin{document}$ i - \Pr \mathop {\rm O}\limits^. + {\rm NO} \stackrel{6}{\longrightarrow} {\rm M}_2 {\rm K} + {\rm HNO}. $\end{document}In addition to AcH, acetone (M2K) and isopropyl alcohol (IPA) are produced in approximately equal amounts. The rate of M2K formation is markedly affected by the ratio S/V of different reaction vessels. It is concluded that the M2K arises as the result of a heterogeneous elimination of HNO from IPN. In a spherical reaction vessel the first‐order rate of M2K formation is given by k5 = 109.4–27.0/θ sec−1: \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm IPN} \stackrel{5}{\longrightarrow} {\rm M}_2 {\rm K} + {\rm HNO}. $\end{document} IPA is thought to arise via the hydrolysis of IPN, the water being formed from HNO. This elimination process explains previous erroneous results for IPN.
Steric factors in the gas‐phase elimination of esters: The pyrolysis of 2,3‐dimethyl‐3‐pentyl acetate
Authors: Cuenca Angela , Chuchani Gabriel 
Published: January 2005

AbstractThe kinetics of the thermal decomposition of 2,3‐dimethyl‐3‐pentyl acetate have been studied at a temperature range of 212–260°C and a pressure range of 30–300 mm Hg. The olefins produced are 2‐ethyl‐3‐methyl‐1‐butene, 3,4‐dimethyl‐trans‐2‐pentene, 3,4‐dimethyl‐cis‐2‐pentene, and 2,3‐dimethyl‐2‐pentene. The reaction is homogeneous, obeys first‐order law, and the value of the rate constant is given by the Arrhenius equation

The directions of elimination and their corresponding partial rates are best explained in terms of purely steric factors.