bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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

Previous 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

The 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

Two‐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

The 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

Hydroxyl 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

The 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

Quantum 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

Nanosecond 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

An 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

The 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

The reaction of 1,3‐cyclopentadiene (CPD) with ground‐state atomic oxygen O(3P), produced by mercury photosensitized decomposition of nitrous oxide, was studied. The identified products were carbon monoxide and the following C4H6 isomers: 3‐methylcyclopropene, 1,3‐butadiene, 1,2‐butadiene, and 1‐butyne. The yield of carbon monoxide over oxygen atoms produced (ϕCO) was equal to the sum of the yields of C4H6 isomers in any experiment. ϕCO was 0.43 at the total pressure of 6.5 torr and 0.20 at 500 torr. We did not succeed in detecting any addition products such as C5H6O isomers.

It was found that 3‐methylcyclopropene was produced with excess energy and was partly isomerized to other C4H6 isomers, especially to 1‐butyne. The excess energy was estimated to be about 50 kcal/mol.

The rate coefficient of the reaction was obtained relative to those for the reactions of atomic oxygen with trans‐2‐butene and 1‐butene. The ratios kCPD+O/ktrans‐2‐butene+O= 2.34 and kCPD+O/k1‐butene+O = 11.3 were obtained.

Probable reaction mechanisms and intermediates are suggested.
The gas‐phase pyrolysis of alkyl nitrites. III. Isopropyl nitrite
Authors: Batt L. , Milne R. T.
Published: January 2005

The 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

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

The directions of elimination and their corresponding partial rates are best explained in terms of purely steric factors.
Triplet excited states of nitronaphthalenes. IV. 1,2‐ and 1,8‐dinitronaphthalenes
Authors: Capellos C. , Suryanarayanan K.
Published: January 2005

Nanosecond flash photolysis of 1,2‐ and 1,8‐dinitronaphthalenes (1,2‐DNO2N; 1,8‐DNO2N) in nonpolar and polar solvents shows transient species with absorption maxima and lifetimes dependent on solvent polarity. In deaerated n‐hexane the absorption maxima and lifetimes (1/K) are 490 nm and 1.0 μsec for 1,2‐DNO2N and 550 nm and 2.5 μsec for 1,8‐DNO2N. In deaerated ethanol the corresponding values are 550 nm and 4.3 μsec for 1,2‐DNO2N and 590 nm and 5.3 μsec for 1,8‐DNO2N. The transient absorptions are attributed to the lowest triplet excited states T1 of the 1,2‐ and 1,8‐DNO2N. The observed red shifts in the absorption maxima of the T1 states are indicative of the extent to which electronic charge is transferred intramolecularly during the T1 → Tn transitions. Furthermore, the increased lifetime of the T1 states with increasing solvent polarity indicates the intramolecular charge transfer character of the T1 states. Changes of dipole moments accompanying the T1 → Tn transitions as well as rate constants for electron or proton transfer and hydrogen abstraction reactions involving the T1 states of 1,2‐ and 1,8‐DNO2N and tributyl tin hydride (Bu3SnH) as the hydrogen donor were determined together with the activation energy of the hydrogen abstraction reaction for the case of 1,2‐DNO2N. The spectroscopic and kinetic data obtained in this work demonstrate that the triplet states of 1,2‐ and 1,8‐DNO2N behave like n → π* states in nonpolar media while in polar solvents the n → π* character of these states is reduced with a simultaneous increase in their intramolecular charge transfer character.
High‐temperature pyrolysis of dimethyl ether
Authors: Aronowitz D. , Naegeli D.
Published: January 2005

The kinetics of pyrolysis of dimethyl ether wexre studied in an adiabatic flow reactor at temperatures between 790 and 950°C. The unimolecular rate constant for the initiating step CH3OCH3 = CH3O + CH3 was found to be k1 = 2.16 × 1015e−76,600/RTsec−1. Aspects of the kinetic mechanism are discussed and a system postulated to account for the high‐temperature products.
Vacuum ultraviolet (147 nm) photolysis of 1,2‐fluorochloroethane
Authors: Ichimura T. , Kirk A. W. , Tschuikow‐Roux E.
Published: January 2005

1,2‐Fluorochloroethane was photolyzed at 147 nm in the pressure range of 3.8–20.9 torr. The effects of added NO, H2S, and large pressures of CF4 were also investigated. The exponential extinction coefficient at 147 nm and 296°K was found to be 147 ± 4 atm−1 · cm−1.

The photochemistry in some respects is similar to that of ethyl chloride. The primary processes again appear to involve at least two excited states. One of these yields ethylene by FCl elimination (Φ ≃ 0.3) and has a lifetime of ∼3.2 × 10−10 sec, with respect to an internal conversion to the vibrationally excited ground state or, more probably, a collisionally induced crossover to a state decomposing mainly by carbonhalogen bond fission. The molecular elimination of HCl, H2, and small amounts of HF also occurs but not apparently from the same state as does FCl. The quantum yields of products with radical precursors, however, are not large, and hence little, if any, of the FCl and probably none of HCl, H2, and HF subsequently dissociates. The vinyl fluoride and vinyl chloride, accompanying the elimination of HF and HCl, are postulated as possible sources of the secondary production of acetylene.
The oxidation of cerous ions by bromate ions comparison of experimental data with computer calculations
Authors: Barkin S. , Bixon M. , Noyes R. M. , Bar‐Eli K.
Published: January 2005

The oxidation of cerous ions by bromate ions in sulfuric acid medium was followed spectrophotometrically under various experimental conditions. The results were compared to the calculated predictions on the basis of a mechanism suggested by R. M. Noyes and collaborators. The computations were done by solving the complete set of the kinetic differential equations. The results of the computations show that the proposed mechanism explains adequately most of our and previous experimental data. In particular, the mechanism predicts the main features of the reaction, namely, the induction and the fast and slow reaction periods which occur during the oxidation.
On the mechanism of interaction between copper (I) and O2
Authors: Gorbunova N. V. , Purmal A. P. , Skurlatov Yu. I. , Travin S. O.
Published: January 2005

The mechanism of the interaction of Cu+‐α,α‐dipyridyl complex (Cu+L2) with O2 in both neutral and acid media was studied by the stopped‐flow method. The dependence of the mechanism on the acidity of the medium was established. In an acid medium H+ participated in a direct O2 reduction to HO2 by interaction with an oxygen adduct L2Cu+O2 formed without displacement of ligand molecules. In a neutral medium the reaction rate was limited by inner sphere charge transfer from Cu+ to O2 to form an oxygen “charge transfer” complex L2CuO+2. The latter interacted either with the second ion Cu+L2 or with the free ligand, or else it dissociated, reversibly or irreversibly, to form a radical anion O−2. The bimolecular rate constants of the oxygen “adduct” and “charge transfer” complex formation appeared to be kbi = (1.0 ± 0.1) × 105 and (1.5 ± 0.2) × 104M−1ċsec−1, respectively. The effective termolecular rate constants of O2 reduction to HO2 in an acid medium (with contribution from H+) and to O−2 in a neutral medium (with contribution from α,α‐dipyridyl) were kter = 2.7 × 108 and 107M−2ċsec−1. The rate constants of the elementary steps were estimated. The auto‐oxidation mechanism of the aquoion and complexes of Cu+ is discussed in terms of the results obtained.
Very low‐pressure pyrolysis (VLPP) of cyclopentene
Authors: King Keith D.
Published: January 2005

The unimolecularity of the thermal dehydrogenation of cyclopentene has been confirmed using the technique of very low‐pressure pyrolysis (VLPP). Application of RRKM theory shows that the experimental unimolecular rate constants obtained over the temperature range of 942°–1152°K are consistent with the high‐pressure Arrhenius parameters given by

where θ = 2.303 RT kcal/mol. These parameters are in good agreement with static and shock tube studies. No firm evidence could be found for any side reactions or reversibility under the experimental conditions used.
Ene reactions of olefins. I. The addition of ethylene to 2‐butene and the decomposition of 3‐methylpentene‐1
Authors: Richard C. , Scacchi G. , Back M. H.
Published: January 2005

The pyrolysis of ethylene–butene‐2 mixtures has been studied in a static system over the temperature range of 689°‐754°k and for initial pressures of each olefin of 20–200 torr. The two main addition products were cyclopentene and 3‐methylpentene‐1. Kinetic evidence indicated that cyclopentene was formed from radical processes while 3‐methylpentene‐1 was formed by the molecular “ene¨︂” addition of ethylene to butene‐2 through a six‐center transition state. The following rate constants were obtained:
equation image
The pyrolysis of 3‐methylpentene‐1 has been studied over the same temperature range and for initial pressures of 20–100 torr. Kinetic evidence showed that the products ethylene and butenes were formed in both radical and molecular processes. Estimates of the rate constant k−1t and k−1c were, however, in reasonable agreement with the measurements of k1t and k1c. The mechanism of the ene reaction is discussed, and it is concluded that the transition state does not involve the formation of a biradical.
Fre‐radical addition to olefins, Part 22. Arrhenius parameters for the addition of trifluoromethyl radicals to vinyl monomers (CH2CHX)
Authors: Low H. C. , Tedder J. M. , Walton J. C.
Published: January 2005

Relative Arrhenius parameters have been determined for the addition of trifluoromethyl radicals to vinyl chloride (XCl), vinyl bromide (XBr), acrylonitrile (XCN), methyl vinyl ketone (XCOCH3), 2‐methylbut‐2‐ene, and to iso‐butene, taking the rate of addition to ethylene as standard. Addition occurred virtually exclusively at the unsubstituted end of all the olefins. The relative rates of addition at 164°C show very little variation. The preexponential terms for addition to the CH2 ends are constant within experimental error, and the small variations in rate are due principally to the activation energy term. The present results are put on an absolute scale using the previously determined Arrhenius parameters for addition to ethylene and are compared with data for other similar monomers determined previously.
The evaluation of rate constants in rate laws containing two terms
Authors: Toby Brian H. , Toby Frina S. , Toby Sidney
Published: January 2005

A simple computerized method using APL is described which gives the rate constants for systems obeying the rate law –d[A]/dt = k1[A][B] + k2[A] m [B]l from sets of concentrations and times. Applications are discussed.
HCO radical kinetics: Conjunction of laser photolysis and intracavity dye laser spectroscopy
Authors: Clark J. H. , Moore C. B. , Reilly J. P.
Published: January 2005

HCO radical at a concentration of about 1014 cm−3 is produced by monochromatic laser photolysis of H2CO with a 0.6 mJ frequency‐doubled, flashlamp‐pumped dye laser pulse. Intracavity dye laser spectroscopy quantitatively monitors HCO absorbance near 614 nm as a function of delay time between photolysis and probing pulses. Rate constants for HCO + O2 and HCO + NO are found to be 4.0 ± 0.8 × 10−12 and 1.45 ± 0.2 × 10−11 cm3 molecule−1 sec−1.
On the oxidation of malonic acid by ceric ions
Authors: Barkin S. , Bixon M. , Noyes R. M. , Bar‐eli K.
Published: January 2005

The oxidation of malonic acid by ceric ions has been investigated in sulfuric acid solution under a variety of conditions. The initial rate at low ceric ion concentrations is first order in each of the two reactants and has an activation energy of 11.6 kcal/mol; the instantaneous rate constant increases somewhat with time during a single run. At higher concentrations of ceric ion, semilogarithmic plots are sigmoid with a reduced rate constant at long times. The rate decreases slightly with increasing sulfuric acid concentration. Rates of carbon dioxide evolution may be much less than rates of ceric ion reduction because of supersaturation effects. The observations can be explained if dissolved oxygen reacts with organic radicals to catalyze the rate of initial attack on malonic acid, but oxygen must also be consumed irreversibly during these reactions. Computations with plausible rate constants have simulated the experimental observations. These oxygen effects can rationalize peculiar almost discontinuous changes in rate when bromomalonic acid is oxidized by ceric ion. These effects may also explain the previously puzzling observation that some Belousov–Zhabotinsky solutions are oscillatory in bulk but become quiescent but excitable when spread in a thin film in contact with air.
On the decarboxylation of oxalic acid in solutions
Authors: Adams Linda J. , Franzus Boris , Huang Thomas T.‐S.
Published: January 2005

The first‐order kinetics and hydrogen kinetic isotope effect of the decarboxylation of oxalic acid in acetophenone were studied in the temperature range of 109.6°–150.0°C. The rate constants, activation parameters, and hydrogen kinetic isotope effect were calculated. Detailed comparison and discussion of the results were made with the data reported in the literature. Kinetic isotope effects and solvent effects on rates should be considered similar in mechanistic and/or theoretical studies in the sense that kinetic isotope effects result from a small perturbation of the reaction coordinate, while the solvent effect causes a general overall variation on the potential energy surface (thereby resulting in a change in the reaction coordinate).
On the reactivity of diethyl hydroxyl amine toward free radicals
Authors: Abuin E. , Encina M. V. , Diaz S. , Lissi E. A.
Published: January 2005

Diethyl hydroxyl amine is an efficient trap for alkyl, alkoxy, and peroxy radicals. The specific rate constant for the reaction of ethyl radicals (gas phase, 25°C), tert‐butoxy radicals (benzene solution, 115°C), and poly (peroxystyryl) peroxy radicals (styrene solution, 50°C) were evaluated as 7.2 × 105, 7.7 × 107, and 2.9 × 105 M−1·sec−1, respectively. Several possible secondary reactions of the nitroxide radicals are discussed.
Kinetics and mechanism of hydrogen–oxygen difluoride reaction in magnesium
Authors: Houser Thomas J.
Published: January 2005

The kinetics of the H2‐OF2 reaction was studied in the temperature range of 160°–310°C at 1 atm total pressure in a magnesium stirred‐flow reactor. Initial concentration ranges were 1/2–1/2 mol·% OF2, 3/16–5 mol·% H2, and 1/4–5.0 mol·% O2; helium was used as the diluent. When the reactants were in a mole ratio of 3/2 (H2/OF2), the rate of disappearance of H2 was 1.5 times that of OF2, consistent with the previously reported stoichiometry. The rate of disappearance of OF2 was strongly influenced by OF2 concentration, weakly influenced by H2 concentration, and inhibited by the oxygen formed in the reaction. An increase in the surface area did not produce a significant change in the rate of reaction. These concentration dependencies led to a proposed ten‐step mechanism from which was derived the following rate equation:

where k0 is a complex combination of elementary rate constants and α and β are elementary rate constants. An Arrhenius treatment of k0 gave

These experimental Arrhenius parameters are lower than those predicted from reported and estimated elementary rate constants. The possibility of heterogeneous contributions is discussed.
A kinetics study of the reactions of OH with several aromatic and olefinic compounds
Authors: Ravishankara A. R. , Wagner S. , Fischer S. , Smith G. , Schiff R. , Watson R. T. , Tesi G. , Davis D. D.
Published: January 2005

The reactions of hydroxyl radicals with eight substituted aromatic hydrocarbons and four olefins were studied utilizing the flash photolysis–resonance fluorescence technique. The rate constants were measured at 298°K using either Ar or He as the diluent gas. The values of the rate constants (k× 1012) in the units of cm3/molec. sec are

(a) OH +o‐xylene → products: (12.9±3.8), 20 torr He; (13.0±0.3), 20 torr Ar; (12.4±0.1), 200 torr He;

(b) OH +m‐xylene → products: (15.6±1.4), 3 torr Ar; (19.4±0.8), 20 torr Ar; (21.4±0.2), 20 torr He; (20.3±1.9), 200 torr Ar; (20.6±1.3), 200 Torr He;

(c) OH +p‐xylene → products: (8.8±1.2), 3 torr Ar; (10.1±1.0), 20 torr He; (10.5±0.6), 200 torr He;

(d) OH + ethyl benzene → products: (7.50±0.38), 3 torr He; (7.06±0.26), 20 torr He; (7.95±0.28), 200 torr He;

(e) OH +n‐propylbenzene → products: (6.40±0.36), 20 torr He; (5.86±0.16), 200 torr He;

(f) OH + isopropylbenzene → products: (7.79±0.40), 200 torr He;

(g) OH + hexafluorobenzene → products: (0.221±0.020), 20 torr He; (0.219±0.016) 200 torr He;

(h) OH +n‐propyl pentafluorobenzene → products: (2.52±0.54), 3 torr He; (3.01±0.76), 20 torr He; (3.06±0.24), 200 torr He;

(i) OH + propylene → products: (25.6±1.2), 20 torr He; (26.3±1.2), 200 torr He;

(j) OH + 1‐butene → products: (29.6±1.9), 3 torr He; (29.4±1.4), 20 torr He;

(k) OH +cis‐2‐butene → products: (43.2±4.1), 3 torr He; (42.6±2.5), 20 torr He;

(l) OH + tetramethylethylene → products: (56.9±1.3), 20 torr He.
Wavelength dependence of the quantum efficiencies of the primary processes in formaldehyde photolysis at 25°C
Authors: Horowitz Abraham , Calvert Jack G.
Published: January 2005

The quantum efficiencies of the primary processes in formaldehyde photolysis (ϕ1 and ϕ2) were determined as a function of wavelength in the range from 2890 to 3380 Å and at 25°C: CH2O + hν → H + HCO (1); CH2O + hν → H2 + CO (2). The estimates of ϕ2 were derived from ΦH2 values obtained in photolyses of CH2O‐isobutene mixtures at high isobutene concentrations where H‐atom scavenging was essentially complete. Values of ϕ1 + ϕ2, obtained from the ΦH2 values from the pure CH2O photolyses, were very near unity at all but the longest wavelengths employed: ΦH2 = ϕ1 + ϕ2 = 1.02 (2930 Å); 1.12 (3130 Å); 1.06 (3150 Å); 1.01 (3250 Å); 1.0 (3335 Å); 0.75 (3380 Å). Our results showed that the onset of photodissociation of CH2O by process (1) was at 3370 ± 10 Å; this corresponds to D(H‐CHO) = 84.8 plusmn; 0.3 kcal/mol. The values of ϕ1 increased regularly with decreasing wavelength from 0 at 3370 Å to ∼0.7 at 3175 Å. Little further variation in ϕ1 occurred from 3175 to 2890 Å. For experiments at λ = 3300 Å, the addition of CO2 (∼300 torr) reduced ϕ2, while the effect on ϕ1 appeared to be small. The present results coupled with the solar irradiance estimates of Peterson [24] and the extinction data for CH2O from McQuigg and Calvert [7] were used to make new estimates of the apparent first‐order rate constants (min−;1 × 103) of process (1) in the lower atmosphere at various solar zenith angles (in parentheses): 2.31 (0°); 2.17 (20°); 1.71 (40°); 0.92 (60°); and 0.17 (78°). The corresponding first‐order rate constants (min−1 × 103) for solar light absorption by CH2O in the lower atmosphere are 7.74 (0°); 7.38 (20°); 6.18 (40°); 3.80 (60°); and 0.96 (78°).
A comparison of two single‐pulse shock‐tube techniques: The thermal decomposition of ethyl chloride and n‐propyl chloride
Authors: Evans P. J. , Ichimura T. , Tschuikow‐Roux E.
Published: January 2005

This investigation presents a detailed examination of the relative reliability of the comparative and absolute rate methods as they are applied to kinetic studies in the single‐pulse shock tube. For this purpose two previously studied reactions, the thermal elimination of HCl from ethyl chloride and n‐propyl chloride, were selected and mixtures of these compounds were shock heated to temperatures in the range of 960°‐1100°K. The experimental results were analyzed by both methods and the rate constants obtained from these analyses are compared with those of previous studies. The advantages and shortcomings of both methods are noted and it is concluded that reliable kinetic data can be obtained by the absolute rate (isolation technique) method with careful examination of the gas‐dynamic flow conditions and taking cognizance of the incident shock deceleration. The limitations of the comparative rate technique encountered in the present study were similar to those detailed in previous investigations.
Unusual H2‐forming chain reaction in the 3130‐Å photolysis of formaldehyde‐oxygen mixtures at 25°C
Authors: Horowitz Abraham , Su Fu , Calvert Jack G.
Published: January 2005

A kinetic study has been made of the 3130‐Å photolysis of CH2O (8 torr) in O2‐containing mixtures (0.02–8 torr) and in the presence of added CO2(0–300 torr) at 25°C. Quantum yields of formation of H2, CO, and CO2and the loss of O2were measured. Φand ΦCOwere much above unity. In an explanation of these unexpected results, a new H‐atom‐forming chain mechanism was postulated involving HO2and HO addition to CH2O: CH2O +hν → H + HCO (1) H + CH2O → H2+ HCO (3) H + O2+ M → HO2+ M (6) HCO + O2→ HO2+ CO (8) HO2+ CH2O → (HO2CH2O) → HO + HCO2H (15) HO + CH2O → H2O + HCO† (16); HCO† → H + CO (19) HO + CH2O → H2O + HCO (17) and HO + CH2O → HCO2H + H (18). When the results are rationalized in terms of this mechanism, the data suggestk16≫k17andk16/k18≅ 0.5. The data require that a reassessment of the relative rates of reactions (7) and (8) be made, since in the previous work HCO2H formation was used as a monitor of the rate of reaction (7) HCO + O2+ M → HCOO2+ M (7). The present data from experiments atP= 8 torr andP= 1–4 torr givek7[M]/(k7[M] +k8) ≥ 0.049 ± 0.017. These data coupled with thek8estimates of Washida and coworkers givek7≥ (4.4 ± 1.6) × 1011l2/mol2·sec for M = CH2O. The reaction sequence proposed here is consistent with the observed deterimental effect of O2addition on the laser‐induced isotope enrichment in HDCO. In additional studies of CH2O‐O2‐isobutene mixtures it was found that Φwas equal to ϕ2as estimated in O2‐free CH2O‐isobutene mixtures. These results suggest that the increase in CO (ν = 1) product observed with O2addition in CH2O photolysis does not result from perturbations in the fragmentation pattern of the excited CH2O, but it is likely that it originates in the occurrence of the exothermic reaction HCO + O2→ HO2+ CO (ν = 1).
Mechanistic details of the Belousov–Zhabotinsky oscillations. II. The organic reaction subset
Authors: Edelson D. , Noyes R. M. , Field R. J.
Published: January 2005

Our previous mechanistic model for the Belousov–Zhabotinsky reaction has been revised to include a more realistic set of reactions for the oxidation pathways of the organic intermediates. A few other rate constants have also been modified to include new information. The revised mechanism reproduces the essential experimental observations, although the periods of oscillation are somewhat too long and oscillations cease at malonic acid concentrations about ten times greater than the observed lower limit. However, the essential features of the mechanism are clearly understood.
A kinetics study of the temperature dependence of the reactions of OH(2Π) with CF3CHCl2, CF3CHClF, and CF2ClCH2Cl
Authors: Watson R. T. , Ravishankara A. R. , Machado G. , Wagner S. , Davis D. D.
Published: January 2005

The flash photolysis resonance fluorescence technique has been utilized to determine the rate constants for three reactions involving the hydroxyl radical [OH(2≅)] and three halogenated C2 alkanes. The nominal temperature range covered was 250–375 K. The compounds studied and the resulting Arrhenius expressions in units of cm3/molec·sec are
equation image
The error limits in these expressions are such that they include any possible systematic errors due to the presence of impurities in the halocarbon samples. Tropospheric lifetimes have been calculated for the above species by combining the above rate constant data with global seasonally and diurnally averaged hydroxyl radical concentrations.
Radical equilibrium studies. II. The thermodynamic parameters of s−butyl
Authors: Marshall Roger M. , Page Nicholas D.
Published: January 2005

The thermal decomposition of azomethane in the presence of propene has been investigated in the range of 568–638°K at reactant partial pressures of up to about 7 torr in the presence of at least 170 torr of argon. The elementary reactions taking place in such conditions are discussed in detail. It is shown that a situation approaching equilibrium is attained between the processes
equation image

Values are obtained for the equilibrium constant K2, which can be described by the equation

Using the best available thermodynamic parameters for methyl and propene, it is concluded that those for s−butyl are in need of adjustment. We recommend the values ΔHf0 (300°K) = 13.8 ± 1.0 kcal/mol and S3000 (1 atm standard state) = 75.6 ± 3.0 cal/mol°K together with group additivity values of the heat capacity. A comparison of measured values of K2 with values calculated from independent measurements of k2 and k−2 shows a discrepancy of about a factor of 3.5.
The kinetics and mechanism of n‐butyraldehyde photolysis in the vapor phase at 313 nm
Authors: Förgeteg S. , Bérces T. , Dóbé S.
Published: January 2005

The photolysis was investigated at 313 nm wavelength, 253–529 K temperatures, and 4 × 10−11‐2 × 10−9 mol·photon/cm2·sec light intensities by determining the quantum yields of 20 reaction products. Primary quantum yields for the seven primary processes and rate constant ratios, rate constants, and Arrhenius parameters for secondary processes were derived on the basis of the suggested reaction scheme. The dependence of the quantum yields of the four major primary processes on experimental conditions was established.
Disproportionation‐to‐combination ratios for cyclohexyl‐h11 and ‐d11 radicals in the gas phase as determined by the radiolysis of water vapor–cyclohexane mixtures
Authors: Fujisaki Noboru , Gäumann Tino
Published: January 2005

In the radiolysis of water vapor containing small concentrations of cyclohexane, the principal products which account for about 98% of all end products are found to be hydrogen, cyclohexene, and bicyclohexyl. Cyclohexene and bicyclohexyl yields were determined over a range of temperatures (70–200°C), total pressures (50–2400 torr), and total doses (0.15–2.0 Mrad). The disproportionation–combination ratio k/k for c‐C6H11 radicals could be determined as 0.56 ± 0.01 from the ratio of cyclohexene to bicyclohexyl yield. By using c‐C6D12, the ratio k/k for c‐C6D11 radicals is found to be 0.38 ± 0.01. Comparison of the reactivity pattern of C6H11 and C6D11 radicals leads to (k)/(k)/(k/k) = 1.47 ± 0.02. The corresponding values for the reactions of c‐C6H11 with c‐C6D11 were also determined.
Bimolecular self‐reactions of phenyl‐substituted phenoxyl radicals studied by flash photolysis
Authors: Khudyakov I. V. , Levin P. P. , Kuzmin V. A. , De Jonge C. R. H. I.
Published: January 2005

Rate, equilibrium, and thermodynamic data for reaction (1) of 2,6‐diphenyl‐4R‐phenoxyl radicals, where R==OCH3 (I), Ph (II), OC2H5 (III), O‐n‐C18H37 (IV), and 2,6‐dicyclohexyl‐4‐phenylphenoxyl radical (V),
equation image
in various solvents are obtained. The k1 values of radicals I to V are within (5.5 ± 1.0) × 107‐(1.4 ± 0.3) × 109M−1·sec−1 in propanol. The solvent effect on k1 for radicals I and II was studied. The dimerization of radical I is diffusion‐controlled in all solvent studies. The dimerization of radical II is viscosity‐dependent but not diffusion‐controlled. Plots of k1 against ET have a V shape. Specific solvent–solute interactions are seeming to be responsible for numerical k1 values of radicals I and II. The solvent effect is more pronounced for “slow” dimerization of radicals II than for “fast” dimerization of radicals I. The minimum k1 values correspond to pyridine and chloroform. The reaction (1) rate strongly depends upon the composition of a chloroform (S)–cosolvent binary mixture. Besides reaction (1) the following reactions proceed in binary mixture:
equation image

(radical I, S‐CCL4 mixture)

(radical II, S‐C6H14 mixture)

(radical II, S‐CCL4 mixture)

In all cases k16 ≪ k15. Factors influencing dimerization rates in strongly nonideal mixtures CH3OH‐CCL4 and CH3OH‐CHCl3 are discussed.
Anionic σ‐complexes from sulfite ion attack on n‐methyl‐N‐β‐hydroxyethyl picramide and its spiro complex. Search for geometric isomerism in 1:2 complexes. An instructive example of complex kinetics
Authors: Bernasconi Claude F. , Wang Hsien‐Chang
Published: January 2005

N‐Methyl‐N‐β‐hydroxyethyl picramide (PH) forms a 1:1 (PHS2−) and a 1:2 (PHS) anionic σ‐complex with sulfite ion. In alkaline solution PH is present mainly in the form of its spiro Meisenheimer complex (M−) which also adds sulfite ion to form a complex MS3−. Rate and equilibrium constants for the various reactions which interrelate the five species PH, PHS2−, PHS, M−, and MS3− (scheme I) were determined. PHS and MS3− can, in principle, exist in the form of two geometric isomers. Despite a careful search by nuclear magnetic resonance and kinetic techniques, no experimental manifestation of this isomerism could be found. Various limiting situations are discussed under which the absence of experimental evidence does or does not exclude the presence of two isomers. Our preferred but unproven interpretation is that in the case of PHS one isomer (trans?) is thermodynamically strongly favored over the other, whereas in the case of MS3− both isomers are of similar thermodynamic stability and have also similar rates. This latter feature would make the isomerism kinetically undetectable. Several other features of scheme I make it an instructive example in complex chemical kinetics.
Study of the reactions of oxygen atoms with carbonothioicdichloride, carbonothioicdifluoride, and tetrafluoro‐1,3‐dithietane
Authors: Slagle Irene R. , Gutman David
Published: January 2005

The reactions of ground‐state oxygen atoms with carbonothioicdichloride, carbonothioicdifluoride, and tetrafluoro‐1,3‐dithietane have been studied in a crossed molecular jet reactor in order to determine the initial reaction products and in a fast‐flow reactor in order to determine their overall rate constants at temperatures between 250 and 500 K. These rate constants are𝔨(O + C2CS) =(3.09 ± 0.54) × 10−11 exp(+115 ± 106 cal/mol/RT),𝔨(O + F2CS) = (1.22 ± 0.19) × 10−11 exp(‐747 ± 95 cal/mol/RT), and𝔨(O + F4C2S2) = (2.36 ± 0.52) × 10−11 exp(‐1700 ± 128 cal/mol/RT) cm3/molec˙sec. The detected reaction products and their rate constants indicate that the primary reaction mechanism is the electrophilic addition of the oxygen atom to the sulfur atom contained in the reactant molecule to form an energy‐rich adduct which then decomposes by C‐S bond cleavage.
Kinetic study of some elementary reactions of sulfur compounds including reactions of S and SO with OH radicals
Authors: Jourdain J. L. , Bras G. Le , Combourieu J.
Published: January 2005

The reactions of S + OH → SO + H (1) and SO + OH → SO2 + H (2) were studied in a discharge flow reactor coupled to an EPR spectrometer. The rate constants obtained under the pseudo‐first‐order conditions with an excess of S or SO were found to be k1 = (6.6 ± 1.4) × 10−11 and k2 = (8.4 ± 1.5) × 10−11 at room temperature. Units are cm3/molec·sec. Besides no reactivity was observed between S and CO2 at 298 K and between CIO and SO2 up to 711 K.