bluuebunny/crossref_metadata_2025 huggingface dataset:
The reactions of CF3 and CD3 radicals with boron trimethyl
Authors: Bell T. N. , Platt A. E.
Published: January 2005

Hydrogen 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

Methods 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

The 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

The 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

The 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

The 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

Absolute 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

A 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

The 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

Electron 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

Instances 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

The 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

Chemically 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.
The homogeneous gas phase H2D2 metathesis at room temperature: Reaction induced by specific vibrational excitation
Authors: Bauer S. H. , Lederman D. M. , Resler E. L. , Fisher E. R.
Published: January 2005

We have demonstrated that reactions for which substantial activation energies are needed can be induced to occur at room temperature via specific vibrational excitation. Indeed, the indications are that the atom‐switching reactions for which Ea > 25 kcal take place with high probability only when the activation energy is localized in the vibrational mode. In this preliminary report on the utilization of the stimulated Raman effect to generate substantial populations in the critical vibrational states required for the homogeneous atom exchange between H2 and D2, we first summarized the historical development of the concept. The experimental arrangement is then described and the analytical results tabulated; the observed dependence on relative concentrations is semiquantitatively rationalized on the basis of a model proposed in 1964. Independent shock tube and molecular beam investigations were similarly accounted for. Attention is called to the discrepancy between the generally concordant experimental results and the ab initio quantum mechanical calculations of the potential energy surface for 4H atoms.
The liquid‐phase oxidation of 2,4‐dimethylpentane
Authors: Mill Theodore , Montorsi Giorgio
Published: January 2005

The initiated oxidation of 2, 4‐dimethylpentane in the neat liquid phase at 100°C with 760 torr O2 gives more than 90% of a mixture of 2,4‐dihydroperoxy‐2,4‐dimethylpentane and 2‐hydroperoxy‐2, 4‐dimethylpentane in a ratio of 7:1. The rate of oxidation depends closely on the [initiator]1/2, consistent with a mechanism in which chain termination occurs mostly by interactions of two 2‐hydroperoxy‐2, 4‐dimethyl‐4‐pentylperoxy radicals. 2, 4‐Dimethylpentane oxidizes only one sixth as fast as isobutane at the same rate of initiation at 100°C. In cooxidations of the same hydrocarbons, it is 0.71 as reactive as isobutane toward any of the peroxy radicals involved. 2, 4‐Dimethylpentane oxidizes 7.5 times as fast at 1.25°C as at 50°C for the same rate of initiation, but the ratio of dihydroperoxide to monohydroperoxide increases only from 5 to 7, corresponding to a difference in activation energy between intramolecular and intermolecular abstraction of 1 kcal/mole. The overall activation energy (Ep – Et/2) is 10.7 kcal/mole, close to the value of 12 kcal/mole found for isobutane. Absolute values for Ep, Et, kp, kr, and kt were derived. Ring closure of 2‐hydroperoxy‐2, 4‐methyl‐4‐pentyl radicals to oxetane, not detected during oxidation, was observed when this radical was generated at 100°C in the near‐absence of oxygen. The ratio of rate constants for oxetane formation and addition of oxygen to the 2, 4dimethyl‐2‐hydroperoxy‐4‐pentyl radical is about 5.4 × 10−5 M at 100°C. Thus, ring closure to oxetane is too slow to compete with addition of oxygen above ˜200 torr. At 100°C, 2, 3‐dimethylbutane gave no evidence of any intramolecular abstraction. However, 2, 3‐dimethylpentane did give at least 12% 2, 4‐glycol or hydroxyketone.
Kinetics of the reactions of cyclopropane derivatives. III. Gas‐phase unimolecular isomerization of cyclopropyl cyanide to the cyanopropenes
Authors: Luckraft D. A. , Robinson P. J.
Published: January 2005

Cyclopropyl cyanide isomerizes in the gas phase at 660°–760°K and 2–89 torr to give mainly cis‐ and trans‐crotonitrile and allyl cyanide, with traces of methacrylonitrile. The reactions are first order, homogeneous, and unaffected by the presence of radical‐chain inhibitors. The rate constants are given by Overall:

cis‐Crotonitrile:

trans‐Crotonitrile:

Allyl cyanide:

where the error limits are standard deviations. On the basis of a biradical mechanism, it is deduced that the CHCN radical center is resonance stabilized by ca. 30 kJ mole−1. Approximate equilibrium data are given for interconversion of the 1‐ and 3‐cyanopropenes.
Kinetics of the I2‐catalyzed isomerization of allyl chloride to cis‐ and trans‐1‐chloro‐1‐propene. The stabilization energy of the chloroallyl radical
Authors: Alfassi Ze'ev B. , Golden David M. , Benson Sidney W.
Published: January 2005

The I2‐catalyzed isomerization of allyl chloride to cis‐ and trans‐ l‐chloro‐l‐propene was measured in a static system in the temperature range 225–329°C. Propylene was found as a side product, mainly at the lower temperatures. The rate constant for an abstraction of a hydrogen atom from allyl chloride by an iodine atom was found to obey the equation log [k,/M−1 sec−1] = (10.5 ± 0.2) −; (18.3 ± 10.4)/θ, where θ is 2.303RT in kcal/mole. Using this activation energy together with 1 ± 1 kcal/mole for the activation energy for the reaction of HI with alkyl radicals gives DH0 (CH2CHCHClH) = 88.6 ± 1.1 kcal/mole, and 7.4 ± 1.5 kcal/mole as the stabilization energy (SE) of the chloroallyl radical. Using the results of Abell and Adolf on allyl fluoride and allyl bromide, we conclude DH0 (CH2CHCHFH) = 88.6 ± 1.1 and DH0 (CH2CHCHBrH) = 89.4 ± 1.1 kcal/ mole; the SE of the corresponding radicals are 7.4 ± 2.2 and 7.8 ± 1.5 kcal/mole. The bond dissociation energies of the CH bonds in the allyl halides are similar to that of propene, while the SE values are about 2 kcal/mole less than in the allyl radical, resulting perhaps more from the stabilization of alkyl radicals by α‐halogen atoms than from differences in the unsaturated systems.
The thermal decomposition of biacetyl
Authors: Knoll H. , Scherzer K. , Geiseler G.
Published: January 2005

The thermal decomposition of biacetyl has been studied at small percentage conversion over the temperature range 375‐417°C. For these conditions, an almost quantitative mass balance was obtained by gas‐chromatographic analysis. The following equation was obtained for the overall reaction
equation image
Between 240° and 277°C, the decomposition of biacetyl initiated by methyl radicals has also been studied. As source of radicals, the thermolysis of azomethane was used. Moreover, the Arrhenius parameters of the following reactions were determined:
equation image
where A is in sec−1 for reaction (1) and in cm3mole−1 sec−1 for reactions (3) and (4); E is in kcal/mole. Evidence is provided that the displacement reaction (4) proceeds by a two step mechanism.
The radiolysis of mixtures of carbon monoxide and hydrogen
Authors: Beattie W. H.
Published: January 2005

The self‐radiolysis of mixtures of CO and tritium (3H2) has been studied at pressures of 0.25 to 1.0 atmospheres, temperatures of −198° to +100°C, and in the presence of added H2O or CO2. The products of decomposition are CO2, 3H2O, C3H4, C23H4, and a white polymer believed to be polyformaldehyde. Initial rates and G values were measured and compared with rates of ion pair formation. The rates of formation of both CO2 and C3H4 are independent of temperature and proportional to the energy absorbed in the 3H2.
A thermal initiation correction to Shepp's rotating sector theory
Authors: Arthur N. L. , Donchi K. F. , de Martinis C.
Published: January 2005

Shepp's rotating sector theory for determining radical recombination rate constants, kb, has been modified to take account of radical production by a concurrent thermal reaction. A theoretical sector curve expression has been derived which gives the average radical concentration under intermittent illumination as a function of α, the ratio of first‐to second‐order radical removal rates, n, the ratio of thermal initiation to photoinitiation, and β, the ratio of the flash time to the half time of second‐order radical removal. Analysis of the sector curves generated by the modified theory shows that n has a greater effect on kb than α and that the rotating sector method should be applied only to those photochemical systems in which termination by first‐order processes is less than 34% (α = 0.52) and thermal initiation is less than 2% (n = 0.02).
Kinetic solvent isotope effect for aromatic nucleophilic substitution in mixtures of EtOH and EtOD
Authors: Cattania M. G. , Beltrame P.
Published: January 2005

Rate coefficients for the ethoxydechlorination of 1‐chloro‐2,4‐dinitrobenzene were measured in mixtures of EtOH and EtOD of different deuterium atom fraction n (n = 0., 0.259, 0.377, 0.581, 0.767, 0.958), at 25°C. The extreme solvent isotope effect, obtained by different extrapolation procedures, is (kD/kH) = 1.90 ± 0.02. The curved variation of kn/kH with n is interpreted by fractionation factor theory in terms of hydrogen‐bonding solvation of ethoxide ion and transition state.
The self‐inhibited pyrolysis of isobutane
Authors: Konar R. S. , Marshall R. M. , Purnell J. H.
Published: January 2005

The pyrolysis of isobutane was investigated in the ranges of 770° to 855°K and 20 to 150 Torr at up to 4% decomposition. The reaction is homogeneous and strongly self‐inhibited. A simple Rice‐Herzfeld chain terminated by the recombination of methyl radicals is proposed for the initial, uninhibited reaction. Self‐inhibition is due to abstraction of hydrogen atoms from product isobutene giving resonance‐stabilized 2‐methylallyl radicals which participate in termination reactions. The reaction chains are shown to be long. It is suggested that a previously published rate constant for the initiation reaction (1)

is incorrect and the value k1 = 1016.8 exp (−81700 cal mol−1/RT)s−1 is recommended. The values of the rate constants for the reactions (4i)

(4t)

(8)

are estimated to be

and

From a recalculation of previously published data on the pyrolysis of isobutane at lower temperatures and higher pressures, the value k11c, = 109.6 cm3 mol−1 s−1 is obtained for the rate constant of recombination of t‐butyl. A calculation which is independent of any assumed rate constants or thermochemistry shows that the predominant chain termination reaction is the recombination of two methyl radicals in the conditions of the present work and the recombination of two t‐butyl radicals in those of our previous study at lower temperatures and higher pressures.
ESR studies on the formation of p‐benzosemiquinone anions over manganese dioxide
Authors: Fukuzumi Shun‐Ichi , Ono Yoshio , Keii Tominaga
Published: January 2005

The reaction between a hydroquinone aqueous solution and manganese dioxide has been investigated by electron paramagnetic resonance spectroscopy. A very stable p‐benzosemiquinone anion is formed when an aqueous solution of hydroquinone is passed through a column of manganese dioxide. The kinetics for the reaction between hydroquinone and manganese dioxide follow the equation

where A0 is the initial concentration of hydroquinone, C is the concentration of p‐benzosemiquinone anions, W is the amount of manganese dioxide, F is the feed rate of a hydroquinone aqueous solution, and k10 and k20 are constants; k10 = 3.1 × 10−2 (cm3/g MnO2· min), k20 = 3.2 (cm3/g MnO2·min).

A mechanism for the reaction is proposed such that Mn(IV) in manganese dioxide is reduced to Mn(II) with hydroquinone from which the semiquinone anion is formed via a neutral semiquinone. The formation of semiquinone anions from several substituted hydroquinones is also discussed.
The role of solvent in some oxygen‐transfer reactions of peroxy compounds
Authors: Ibne‐Rasa Khairat M. , Edwards John O.
Published: January 2005

Solvent–solute interactions in the peroxyacid oxidations are believed to be specific rather than electrostatic in nature. The kinetic solvent effects reported for the oxidations of organic sulfides, olefins, acetylenes, nitrosobenzenes, thioketones, and aryl sulfines reveal that in each case the rates are fast in nonbasic solvents (e.g., benzene, nitrobenzene, and halogenated hydrocarbons) relative to those in basic solvents such as DMF, dioxane, and alcohols. The rates in CF3CH2OH and aqueous or partially aqueous media are again higher than those in the basic solvents. This remakably similar pattern of sensitivity of rates to changes in the solvent nature appears to be characteristic of these oxidations as demonstrated by the existence of linear free‐energy relationship. The behavior is best understood in terms of cyclic transition states for these oxidations in which charge separation is avoided by intra‐ or intermolecular hydrogen bonding depending on the nature of the solvent. Solvent effects on sulfoxide oxidation and on oxidations by hydrogen peroxide and t‐butylhydroperoxide are also briefly discussed.
Rate constants of the combination of methyl radicals with nitric oxide and oxygen
Authors: Laufer Allan H. , Bass Arnold M.
Published: January 2005

Rate constants for the combination of methyl radicals with NO and O2 have been measured by flash photolysis of azomethane coupled with product analysis by gas chromatography. Values of the rate constants have been obtained over the pressure region from 50 to 700 torr with He, N2, and Ar as quenching molecules.

The high‐pressure limits were obtained through an RRKM model calculation and were found to be

The rate constants were measured relative to the methyl combination reaction k1 with k1 = 9.5 × 10−11 cm3/molec · sec. The RRKM model suggests D0(CH3O2) = 32 ± 3 kcal/mole.
Model for a three‐center decomposition reaction. I. Perfluorodiazirine
Authors: Tschuikow‐Roux E. , Jung K. H.
Published: January 2005

A semiempirical approach has been used to evaluate rate parameters for a three‐center decomposition reaction from the point of view of transition state theory, with perfluorodiazirine serving as the prototype molecule. Several activated complex models are considered in which the reaction coordinate is chosen as the ∡ NCN bending mode. The constraints imposed include the principle of concerted bond‐order conservation in passing from the initial to the final state, and use is made of empirical bond order–bond length and bond order–force constant relationships. The geometric configuration of the transition state sought is one which conforms with the lowest energy path and is also consistent with the observed entropy of activation. The potential energy of activation is taken as the optimum difference in binding energies (based on the INDO method) between the transition and initial states, and the critical energy is obtained by applying a correction for the zero‐point energy difference, derived from normal coordinate analysis. Satisfactory agreement is found in the case of the activated complex model for which the total bond order is conserved and bonds undergoing rupture are assigned a fractional bond order (FBO) of 2/3, derived from the postulate (FBO) = α/β whe re α(=2) is the number of bonds breaking, and β(=3) is the number of bonds undergoing change in the ring opening.
Thermal decomposition of trimethylene sulfone and 3‐methyl sulfolane
Authors: Cornell Douglas , Tsang W.
Published: January 2005

Trimethylene sulfone and 3methyl sulfolane have been pyrolyzed using a modification of the toluene flow method and a comparative rate technique. The main decomposition reactions are
equation image
where k1=1016.1±0.3 exp(−28,100±500/T) sec−1 and k2=1016.1±0.4 exp(−33,200±750/T) sec−1.
The kinetics of the decarboxylation of n‐butylmalonic acid in alkanols and amines
Authors: Clark Louis Watts
Published: January 2005

Rate constants and activation parameters are reported for the decarboxylation of n‐butylmalonic acid in four normal alkanols (hexanol1, octanol1, decanol1, and dodecanol1) and in five amines (aniline, N‐methylaniline, N‐ethylaniline, N‐n‐propylaniline, and N‐n‐butylaniline). Both ΔH‡ and ΔS‡ of the reaction in both homologous series decrease regularly with increasing length of the hydrocarbon chain of solvent. If we compare data for the reaction in alkanol–amine pairs containing the same total number of carbon atoms in the molecule, we find that the ΔH‡ values are identical, but that the value of ΔS‡ is 0.8 eu/mole higher for the reaction in the amines as compared with the alcohol. The rate constant, at all temperatures, is 1.5 times as large in the amine as it is in the corresponding alcohol. Empirical equations are deduced relating the parameters ΔH‡ ΔS‡ ΔG‡ and k of the reaction to the parameters n and T, where n is the total number of carbon atoms in the solvent molecule and T is the absolute temperature. The results reported herein are compared with previously reported data for malonic acid.
The homogeneous reaction CD4 + NH3 → CD3H + NH2D: The effect of ethane impurities
Authors: Lifshitz Assa , Schechner Pinhas
Published: January 2005

The homogeneous exchange reaction between tetradeutero methane and ammonia was studied behind reflected shocks in a single‐pulse shock tube over the temperature range of 1300–1800°K. The rate of production of CD3H at the early stages of the reaction in mixtures ranging between 1‐4.5% NH3 and 1–4.3% CD4 in argon is given by d[CD3H]/dt=kb [CD4]0[NH3]0, where kb=8 × 1016 exp (−65.3 × 103/RT) cm3/mole·sec. This activation energy is considerably lower than the one that may be expected on the basis of a pure free radical mechanism. It is rationalized by C2D6 impurities in the methane. No clear answer can be obtained regarding the role of a four‐center intermediate in this reaction.
A study of the mechanism and kinetics of the reaction of O(3P) atoms with propane
Authors: Harker Alan B. , Burton C. S.
Published: January 2005

The mechanism and kinetics of the reaction of O(3P) atoms with propane were investigated using molecular modulation spectroscopy, with the O(3P) atoms being generated by the Hg photosensitized decomposition of N2O. The absorption spectrum of the X2II3/2 state of OH was observed in the ultraviolet between 307 and 309 nm, and it was confirmed that OH was the product of the O(3P) reaction with propane. The rate constants for the reactions of O(3P) and OH with propane were determined to be 3.9±0.7±1010 and 1.19±0.05±1012 cm3/mole·sec, respectively, at T=56±5°C.
VLPP unimolecular rate theory
Authors: Barker John R.
Published: January 2005

The exact theory is derived for the thermal unimolecular decomposition of gas‐phase molecules activated and deactivated exclusively through heterogeneous collisions with the walls of a spherical vessel. This theory is appropriate for the treatment of very‐low‐pressure pyrolysis (VLPP) experiments and other experiments carried out at very low pressures. It is shown, however, that the exact theory is closely approximated by ordinary gas‐phase unimolecular rate theory and that for practical application to experiments the results of both theories are indistinguishable.
The thermal unimolecular decompositions of C2H5Cl, i‐C3H7Cl, and t‐C4H9Cl
Authors: Heydtmann Horst , Dill Bernd , Jonas Reinhard
Published: January 2005

The thermal decompositions of ethyl chloride, iso propyl chloride, and tertiary butyl chloride were studied in a static system in the pressure range of 0.1–300 torr. The following Arrhenius equations for the high‐pressure limit were obtained:
equation image
The pressure dependence of the first‐order rate constant (falloff) for these three unimolecular dehydrochlorination reactions, starting with approximately equal kω values, by proper choice of temperature, is shifted to lower pressures with increasing molecular size:
equation image
Thermal isomerization of cis‐ or trans‐2‐butene. The unimolecular elimination of hydrogen from cis‐2‐butene around 500°C
Authors: Masson D. , Richard C. , Martin R.
Published: January 2005

An analytical and kinetic study of the thermal reaction of cis‐ or trans‐2‐butene has been performed in a static system over the temperature range of 480–550°C and at a low extent of reaction and initial pressures of 10–100 torr.

The rate constant of the unimolecular cis–trans isomerization of cis‐2‐butene, determined under the conditions

(2.3 RT in cal/mole) is in good agreement with previous measurements made at lower pressures.

A comparison between the formation rates of hydrogen from the thermal reactions of cis‐ and trans‐2 butene around 500°C leads to the rate constant value

(2.3 RT in cal/mole) for the unimolecular 1,4hydrogen elimination from cis2butene.
Thermal stability of alcohols
Authors: Tsang Wing
Published: January 2005

3,3‐Dimethylbutanol‐2 (3,3‐DMB‐ol‐2) and 2,3‐dimethylbutanol‐2 (2,3‐DMB‐ol‐2) have been decomposed in comparative‐rate single‐pulse shock‐tube experiments. The mechanisms of the decompositions are
equation image

The rate expressions are

They lead to D(iC3H7H) – D((CH3)2(OH) CH) = 8.3 kJ and D(C2H5H) – D(CH3(OH) CHH) = 24.2 kJ.

These data, in conjunction with reasonable assumptions, give

and

equation image

The rate expressions for the decomposition of 2,3‐DMB‐1 and 3,3‐DMB‐1 are

and
Comparison between experimental and calculated results on the decomposition of chemically activated alcohols
Authors: Tsang Wing
Published: January 2005

The life times of chemically activated alcohols have been determined using the high‐pressure unimolecular rate parameters for thermal decomposition of alcohols from shocktube studies and RRKM calculations. They are compared with literature numbers (from insertion of 0(1D) into hydrocarbons). It is suggested that in some cases singlet oxygen carries excess energy into the hydrocarbon. The consequences of such an assumption are explored and discrepancies with previously published conclusions discussed.
Reactions of methyl radicals with acetaldehyde and acetaldehyde‐d1. I. relative rates of atom abstraction reactions at 785°K
Authors: Bárdi I. , Bérces T. , Szilágyi I.
Published: January 2005

The role of ethenoxy radicals in the pyrolysis of CH3CDO was studied by mass spectrometric analysis of the isotopic composition of the methane, ethane, and recovered aldehyde. Experimental evidence was obtained for the formation of ethenoxy radicals and for their reaction with acetaldehyde.

Mixtures of CH3CHO and CH3CDO were pyrolyzed in order to minimize H‐D scrambling in the methyl group of the aldehyde. A kinetic treatment of the methyl radical reactions

equation image

and

equation image

furnished the rate constant ratios (k2a + k2b)/k1a = 2.7 and k1b/k1a = 0.62 at 785°K. It is concluded that at the usual temperatures of CH3CHO pyrolysis the rate of alkyl hydrogen capture is comparable to that of formyl hydrogen abstraction.

The results and conclusions are discussed and compared with previous work.
Kinetics of bimolecular chemical reaction by a modified diffusion equation
Authors: Kondo Shingo , Takano Yo
Published: January 2005

In order to describe the kinematical behavior of the bimolecular chmical reaction in a dilute solution of species characterized by a single diffusion coefficient and by some nonuniform spatial distribution of the active site, a diffusion equation with a simple sink term is derived by reducing the many‐body problem to a one‐body problem. The equation is normalized with the concentration of unreacted particles. The so‐called second‐order reaction rate constant can be calculated from the solution of the equation. The equation is applied to the intermolecular termination reaction of polymer radicals on the assumption of free draining. The reaction rate constant gradually decreases with time.
The photolysis of SO2 at 3080 Å in the presence of cis‐ and trans‐1,2‐difluoroethylene
Authors: Wampler Fred B.
Published: January 2005

The photolysis of SO2 at 3080 Å, FWHM = 150 Å, and 22°C has been investigated in the presence of cis‐ and trans‐C2F2H2. Quantum yield measurements for the photosensitized isomerization of cis‐C2F2H2 to trans‐C2F2H2 have been made for a variation in the [SO2]/[cis‐C2F2H2] ratio from 0.992 to 253. The results fit a mechanism which is consistent with the SO2(3B1) state being the reactive excited state of sulfur dioxide. A mechanism employing only the SO2(1B1) and SO2(3B1) excited states is quite satisfactory to rationalize the data. A value for the SO2 collisionally induced intersystem crossing efficiency from SO2(1B1) to SO2(3B1) of 0.35 ± 0.14 was estimated while the cis‐C2F2H2 efficiency was found to be 0.030 ± 0.012. The rate constant at 22°C for the removal of SO2(3B1) molecules by cis‐C2F2H2 was found to be (1.43 ± 0.13) × 10101./mole · sec. A photostationary composition, [cis]/[trans] = 1.0 ± 0.1, was found from prolonged irradiations of SO2 in the presence of the cis and trans isomers.
The kinetics of aquation and racemization of some cis‐ chloro‐, hydroxo‐, and aquabis(ethylenediamine)(amine)cobalt(III) complexes
Authors: Fenemor D. R. , House D. A.
Published: January 2005

Aquation rates forcis‐CoCl(en)2(A)2+ (A = 3,5‐lutidine, imidazole, N‐methylimidazole, benzimidazole) have been determined by halide release titration in 1.0 M HNO3 at 50–80°C. Kinetic parameters are (in the above order of A) 107k298 (sec−1), 7.4, 5.7, 1.3, 9.7; Ea (kJ/mole), 103, 101, 130, 112; log PZ (sec−1), 11.89, 11.53, 16.04, 13.58; ΔS298‡ (J/°K· mole),−26, −32, +54,+7. Rates of racemization for active cis‐Co(en)2(A)‐(OH2)3+ were measured spectropolarimetrically in 0.1 M HClO4, 0.02 M Hg2+ for A = ammonia, cyclohexylamine, 3,5‐lutidine, N‐methylimidazole. Kinetic parameters are (units as above) 109k298 = 1.8, 38.0, 7.7, 1.7; Ea = 150, 135, 152, 157; log PZ = 17.49, 16.18, 18.56, 18.87; ΔS298‡ = +82, +57, +102,+108. Rates of racemization of the active hydroxo complexes cis‐Co(en)2(A)(OH)2+ (A = NH3, CH3NH2, 3,5‐lutidine, imidazole) were measured similarly at pH = 8 (π = 2.0, NaClO4). The racemization of the hydroxo is ca. (3–4) × 103 faster than for the corresponding aqua complex. Kinetic parameters are 106k298 = 2.55, 7.2, 30.1, 7.0; Ea = 138, 123, 122, 128; log PZ = 18.58, 16.39, 16.85, 17.18; ΔS298‡ = +102,+60, +69,+76. Racemization rates for aquahydroxo mixtures (A = CH3NH2, 3,5‐lutidine, imidazole) were also determined in the pH range of 4–8 (θ = 2.0, NaClO4) at 50.6°C, and pKa data calculated from the pH versus k plot are 5.50, 5.65, and 6.40, respectively, for A.
The decarboxylation of methylmalonic acid and n‐octadecylmalonic acid in normal alkanols
Authors: Clark Louis Watts
Published: January 2005

Rate constants and activation parameters are reported for the decarboxylation of methylmalonic acid and n‐octadecylmalonic acid in three normal alkanols (hexanol‐1, octanol‐1, and decanol‐1). Enthalpies of activation for both substrates in the various solvents are found to be a linear function of the number of carbon atoms or methylene groups in the hydrocarbon chain of the solvent. For both reaction series the isokinetic temperature is found to be equal to the melting point of the substrate. The free energy of activation at the isokinetic temperature in kcal/mole is 29.0 for n‐octadecylmalonic acid and 29.4 for methylmalonic acid. Based on the results of the present investigation as well as on previously reported data in the case of malonic acid and n‐butylmalonic acid, an empirical method of calculating the rate of reaction for the decarboxylation of malonic acid and its n‐alkyl derivatives in normal alkanols is proposed. As a further test of the method of calculation the decarboxylation of n‐dodecylmalonic acid in heptanol‐1 at 110.30°C was studied. The calculated value of the pseudo‐first‐order specific reaction velocity constant of the reaction agreed with the experimental value to within about 0.1 percent.
Radiation‐induced hydrogen fluoride formation in fluorine‐containing ethanes and ethenes
Authors: Chu Chao‐kang , Heckel Edgar
Published: January 2005

Several fluorine‐containing ethanes (monofluoro, 1,1‐difluoro, 1,1,1‐trifluoro, 1,1,2‐trifluoro, 1,1,2,2‐tetrafluoro, and pentafluoro) and ethenes (1,1‐difluoro and trifluoro) form hydrogen fluoride when irradiated with gamma rays in the gas phase at 25°C. Hydrogen fluoride is apparently formed from fluoroethanes by a mechanism which involves formation of an intermediate semiion pair. We observed identical HF yields both in the absence and presence of molecular oxygen, except for monofluoroethane. A reduction of G(HF) with increasing sample pressure, for example, of 1,1,2,2‐tetrafluoroethane, indicates that collisional stabilization of excited fluoroethane molecules competes with the process of HF elimination. High G values for HF and CO2 in mixtures of CF2CFH and O2 reveal the occurrence of a chain reaction.
Bimolecular rates of association of amines with boron trifluoride: Theoretical consideration
Authors: Chang Do Ren
Published: January 2005

The application of the RRKM theory to the reverse bimolecular reaction of the amine–borontrifluoride system has been made. The results are in good agreement with experiments.
Some reactions of the isopropyl radical
Authors: Szirovicza L. , Márta F.
Published: January 2005

The decomposition of ethane sensitized by isopropyl radicals was studied in the temperature range of 496–548°K. The rate of formation of n‐butane, isopentane, and 2,3‐dimethylbutane were measured. The expression k1/k2½ was found to be

where k1 and k2 are rate constants of

equation image

The decomposition of propylene sensitized by isopropyl radicals was studied between 494 and 580°K by determination of the initial rates of formation of the main products. The ratio of k13/k21/2 was evaluated to be

where k13 is the rate constant for

equation image

The isomerization of the isopropyl radical was investigated by studying the decomposition of azoisopropane. The decomposition of the iso‐C3H7 radical into C2H4 and CH3 was followed by measuring the rate of formation of C2H4. On the basis of the experimental data, obtained in the range of 538–666° K, k15/k2½ was found:

where k15 is the rate constant of

equation image
Excited‐state kinetics in the photolysis of azoethane and hexafluoroazomethane at 366 nm, up to one atmosphere pressure, and from room temperature to 150°C
Authors: Pritchard G. O. , Servedio F. M. , Marchant P. E.
Published: January 2005

The photochemistry of azoethane and hexafluoroazomethane at 366 nm has been reinvestigated up to 1 atm pressure, and over a range of temperature from 27 to 150°C. The Stern‐Volmer type quenching plots primarily demonstrate the decomposition of a single electronic and vibrationally excited state for azoethane, but competitive photodissociation from two different electronic and vibrationally excited states, which was previously postulated for hexafluoroazomethane and azoisopropane, is confirmed for hexafluoroazomethane. It is concluded, however, that two different electronic and vibrationally excited photodissociating states are present in azoethane photolysis, but that one of them is difficult to detect, at least by the present approach

Photosensitization with biacetyl at 436 nm also causes the dissociation of azoethane, and this is probably from the vibrationally equilibrated first triplet state. The energy barrier for this process was found to be 5.0 kcal/mol.
Vibration–vibration energy exchange between 15N14NO and CO
Authors: Suitor Jerry W. , Kuby W. C.
Published: January 2005

The temperature dependence of the vibration–vibration energy transfer between the v3 mode of 15N14NO and the first vibrational level of CO was determined over a range of 680 to 1300°K using a shock tube. Several mixtures of 15N14NOCO were tested, diluted in 95% Ar. The resulting exothermic transfer probabilities for the reaction,

are compared to previous work on N2O—CO. The results for 15N14NOCO exhibit a more pronounced direct temperature dependence than for N2O—CO even though the process has a closer resonance (ΔE = 59 cm−1 for 15N14NOCO and ΔE = 81 cm−1 for N2OCO).
The heats of formation of NO3− and NO3− association complexes with HNO3 and HBr
Authors: Davidson J. A. , Fehsenfeld F. C. , Howard Carleton J.
Published: January 2005

The equilibrium constant for the reaction
equation image
has been determined between 331 and 480°K using a variable‐temperature flowing afterglow. These data give ΔH°(1) = ‐1.03 ± 0.21 kcal/mol and ΔS°(1) = —4.6 ± 1.0 cal/mol°K. When combined with the known thermochemical values for HBr, Br−, and HNO3, this yields ΔH(NO3−) = ‐74.81 ± 0.54 kcal/mol and S(NO3−) = 59.4 cal/mol·°K. In addition ΔHn‐1,n and ΔSn‐1,nfor the gas‐phase reactions

were determined for n = 2 and 3. The implications of these measurements to gas‐phase negative ion chemistry are discussed.
Relaxation of DF(v = 1) by various polyatomic molecules
Authors: Bott Jerry F.
Published: January 2005

By means of the technique of laser‐induced fluorescence, the room‐temperature vibrational relaxation of DF(v = 1) has been studied in the presence of several polyatomic chaperones. The rate coefficients obtained [in units of (μ;sec·torr)−1] are CH4, 0.22; C2H6, 0.61; C4H10, 1.26; C2H2, 4.0 × 10−2; C2H2F2, 1.86 × 10−2; C2H4, 0.175; CH3F, 0.36; CF3H, 1.95 × 10−2; CF4, 1.0 × 10−3; CBrF3, 5.6 × 10−4; NF3, 5.1 × 10−4; SO2, 1.27 × 10−2; and BF3, 7.1 × 10−3. Results are also reported for vibrational relaxation rate coefficients for HF(v = 1) in the presence of the following chaperones: CH4, 2.6 × 10−2; C2H6, 5.9 × 10−2; C3H8, 8.4 × 10−2; and C4H10, 0.128. A comparison of DF and HF results indicates that for deactivation by CnHn+2, rate coefficients for DF are approximately an order of magnitude larger than for HF. The deactivation rate coefficient of DF(v = 1) by CH4 was found to decrease with increasing temperature between 300 and 740°K.
Collisional energy transfer in the reactions I + NO + M → INO + M and I + NO2+ M → INO2+ M
Authors: Van Den Bergh H. , Benoit‐Guyot N. , Troe J.
Published: January 2005

The low‐pressure recombination rate constants of the reactions I + NO + M → INO + M (with 14 different M) and I + NO2+ M → INO2+ M (with 26 different M) have been measured at 330°K by laser flash photolysis. The collision efficiencies βcare analyzed and compared with other thermal activation systems. Whereas βcincreases in one reaction with an increasing number of atoms in M, practically no such effect is found when, for the same M, different reactions with varying complexities of the reacting molecules are considered.
Activation energy and nonequilibrium effects in thermal reactions
Authors: Penner Alvin P. , Bhattacharjee Rakhal C. , Forst Wendell
Published: January 2005

Calculations of the nonequilibrium rate constant for the model system H2O2 + M → 2 OH + M over the temperature range of 300–1900°K, assuming that only vibrational, or that both vibrational and rotational, energy is transferred in a collision, show that (1) inefficient energy transfer leads to a distinctly non‐Arrhenius temperature dependence, the nonlinearity being in principle different for different M, and (2) despite different activation energies for different M, the order of M efficiencies is preserved throughout the temperature range. A reversal of M efficiencies can occur only if there is a change of mechanism of the reaction over the temperature range investigated.
Energy transfer in unimolecular reactions at high temperatures
Authors: Barnard J. A. , Parrott T. K.
Published: January 2005

The application of modern theories of energy transfer to unimolecular reactions taking place at very high temperatures is discussed. It is shown that the efficiency of energy transfer for both reactant–reactant and reactant–inert diluent collisions may be substantially smaller than the values determined experimentally at lower temperatures. Consequently at high temperatures unimolecular falloff effects, particularly in some shock‐tube measurements, may be greater than has been believed hitherto.

The application of these calculations to the unimolecular reactions of cyclopropane, cyclobutane, and cyclohexene at temperatures around 1300°K is discussed, and it is shown that under shock‐tube conditions the apparent first‐order rate coefficient may be at least ten times less than the high‐pressure limiting value.