bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of the reactions of singlet molecular oxygen (O21Δg) with organic compounds in the gas phase
Authors: Huie Robert E. , Herron John T. 
Published: January 2005

AbstractThe reactions of singlet molecular oxygen (O21Δg) with a series of organic compounds have been studied in the gas phase at 298°K. The concentration of singlet molecular oxygen was determined by titration with 2,5‐dimethylfuran. The titration technique was checked using a photoionization technique. Absolute rate constants were measured on the basis of the loss of organic reactant and, in some cases, of singlet molecular oxygen. It was found that the usual method of producing singlet molecular oxygen in the gas phase can also, under some conditions, allow reactive species other than singlet molecular oxygen to enter the reactor, leading to serious errors in the determination of rate constants. This problem was eliminated by carrying out the rate measurements in the presence of a small amount of nitrogen dioxide a radical scavenger.
Kinetics of the gas‐phase reaction of allyl alcohol with iodine. The heat of formation and stabilization energy of the hydroxyallyl radical
Authors: Alfassi Ze'ev B. , Golden David M. 
Published: January 2005

AbstractThe reaction of iodine with allyl alcohol has been studied in a static system, following the absorption of visible light by iodine, in the temperature range 150‐190°C and in the pressure range 10‐200 torr. The rate‐determining step has been found to be
equation image
and k3 is consistent with the equation
equation image
From the activation energy and the assumption E‐3 = 1 ± 1 kcal mol−1, it has been calculated that
equation image
kcal mol−1. The stabilization energy of the hydroxyallyl radical has been found to be 11.4 ± 2.2 kcal mol−1.
Flash photolysis of s‐trinitrobenzene solutions
Authors: Capellos C. , Suryanarayanan K. 
Published: January 2005

AbstractFlash photolysis of s‐trinitrobenzene (TNB) aerated solutions in alcohols generates a transient species with absorption maxima at 430 and 510 nm. The yield of the transient is a function of oxygen concentration, and its rate of formation is viscosity dependent. In deaerated solutions instead of the transient, a brown permanent product, identified as a charge transfer (CT) complex with absorption maxima at 470 and 550 nm, is produced. These species are formed only in polar solvents with relatively high proton affinity. The data suggest an intermolecular proton transfer, from electronically excited TNB to the solvent forming the anion magnified image The anion thereby produced interacts with oxygen in aerated alcohols to form the transient attributed to CT complex magnified image while in deaerated alcohols the anion reacts with the solvent to produce RO−, which leads to the CT complex RO…−TNB. This mechanism is supported by detailed kinetic and spectroscopic studies.
A new mechanism for gas phase ozone–olefin reactions
Authors: O'Neal H. Edward , Blumstein Carl 
Published: January 2005

AbstractA new mechanism for gas phase ozone‐olefin reactions is proposed. The mechanism involves biradical intermediates which can react in a variety of ways. One of the possible reaction modes corresponds to the Criegie mechanism originally proposed to explain solution ozonolysis reactions and generally also accepted in the past for gas phase reactions. However, an examination of the gas phase data on ozone–olefin reactions and of the thermochemical and kinetic requirements for these reactions indicates that the Criegie reaction mode may be the least important of various other reaction possibilities. Those other reaction possibilities involve intramolecular H abstractions and rearrangements in biradical intermediates. The proposed mechanism provides very reasonable explanations for a number of unusual observations on gas phase ozonolysis. These are the formation of peroxidic bound products, aldehyde and 1,2‐dicarbonyl product fluorescences, and unexpected carbonyl product formations.
Homogeneous gas‐phase pyrolyses with a wall‐less reactor. III. The oxygen–ethane reaction. A double reversal in oxygen and surface effects
Authors: Taylor Jay E. , Kulich Donald M. 
Published: January 2005

AbstractThe impact of surface and oxygen on the oxidative pyrolysis of ethane at temperatures above 590°C was studied using a wall‐less reactor. At very low conversions under homogeneous conditions, ethene formation begins at the same temperature regardless of whether oxygen is present or absent. Between 0.00 and 0.13% conversion (592–632°C), the rate with oxygen is actually less than the rate in the absence of oxygen. A reversal occurs at about 633°C above which oxygen has a promoting effect. It is concluded that under homogeneous conditions the initiation step in the oxygen‐promoted pyrolysis is the same as in the oxygen‐free pyrolysis; therefore, initiation by direct attack of oxygen on ethane does not make an important contribution. The decrease in rate observed upon addition of oxygen implies the formation of the relatively unreactive HO2 · radical. As conversion of the HO2 · radical to the more reactive HO · radical becomes significant, the reaction is highly accelerated. If a stainless steel surface is added, the reaction is inhibited at higher conversions in the presence of oxygen. Again at low conversions, a second reversal occurs, and the stainless steel surface acts as a promoter below 649°C. The rate of surfacecatalyzed ethene formation at 590°C equals the rate of homogeneous ethene formation at 630°C.
Very low‐pressure pyrolysis. IX. The decomposition of azoethane, azoisopropane, and 2,2′‐azoisobutane
Authors: Perona Michael J. , Beadle Peter C. , Golden David M. 
Published: January 2005

AbstractThe very low‐pressure (VLPP) technique was used to study the pyrolysis of azoethane (AE), azoisopropane (AIP), and 2,2′‐azoisobutane (AIB). The low pressure rate constants were related to the high‐pressure Arrhenius parameters by means of the RRKM theory. This procedure in itself does not yield an unambiguous set of parameters. However, thermochemical and kinetic arguments are given which support the following values of log k∞ for the pyrolysis of AE, AIP, and AIB, respectively: 16.4–49.7/θ 16.6–47.9/θ, and 16.4–42.8/θ, where θ = 2.303RT in kcal/mole. The flow dependence of kuni was used to estimate the collisional efficiencies of the azo compounds relative to the wall.
Comparisons between experimental and calculated rate constants for dissociation and combination reactions involving small polyatomic molecules
Authors: Tsang Wing 
Published: January 2005

AbstractThe experimental results on decomposition and combination reactions involving O3, HNO3, NH3, C2N2, and NO2Cl over extended temperature and pressure ranges are compared with the deductions from RRKM calculations. Quantitative fits of the data over the entire range are possible only if the external (overall) rotations are assumed to be involved in the reactions. Recommended rate constants for the reactions O + O2+ N2→ O3+ N2and OH + NO2+ N2→ HNO3+ N2are presented.
Low‐pressure thermal decomposition of ONBr and ONCl in shock waves
Authors: Maloney K. K. , Palmer H. B. 
Published: January 2005

AbstractRate constants for the low‐pressure unimolecular decomposition of ONBr and ONCl in an argon bath have been determined at temperatures in the vicinity of 1000°K. Both molecules exhibit the usual depression of the observed activation energy below the bond dissociation energy. The Arrhenius expressions obtained are (units of cc mole−1 sec−1):

Treatment of the data by the classical RRK theory yields s ≅ 2.7 ± 1 for ONCl and 3.0 ± 0.6 for ONBr. Coupling the shock tube results for ONCl with lower‐temperature data from Ashmore and Burnett [3], one obtains s ≅ 2.5 ± 0.5 and λ ≈︁ 1. If it is assumed that s is also 2.5 for ONBr, then one finds the surprising (but tentative) result that λONClAr/λONBrAr ≈︁ 3 to 4.
Basic elimination of HCl from chlorinated ethanes
Authors: Walraevens R. , Trouillet P. , Devos A. 
Published: January 2005

AbstractChloroethanes react with aqueous caustic to yield either elimination or substitution products. The reaction rates were measured for the dichloroethanes, trichloroethanes, tetrachloroethanes, and pentachloroethane between 283 and 353°K. The constants of HCl eleminations referring to the rate equation

are given by

all rate constants being in 1./mole·s and R in cal/mole· deg.With ethyl chloride, 1,1‐dichloroethane, and 1,1,l‐trichloroethane, the elimination is not observed and a slow substitution takes place. The influence of chlorine substituents on both sides of the molecule on mechanism and rate parameters is discussed.
The steady‐state approximation: Fact or fiction?
Authors: Farrow L. A. , Edelson D. 
Published: January 2005

AbstractThe kinetic equations for an 81‐reaction model of a photochemical smog chamber have been solved using a complete numerical integration as well as a quasi‐steady‐state approximation (QSSA) procedure. The two sets of results differ markedly in their prediction of experimentally significant factors such as the hydrocarbon depletion rate and the ozone and (NO)x peaking times. The sources of the discrepancy are traced to the fact that the assumed steady‐state conditions were not satisfied, leading to errors in the concentrations of intermediate radicals which in turn affect critical rates in the reaction model.The occurrence of such discrepancies in various types of reaction models, and with different QSSA strategies, is discussed, and it is concluded that the extent of such errors in QSSA calculations cannot be reliably predicted. Their impact on conclusions regarding reaction mechanisms and rate constants can surpass uncertainties in experimental data; conversely the credibility of predictions derived through QSSA calculations becomes highly suspect. Since recently devloped methods for complete numerical integration of systems of kinetic equations are now available, it is recommended that these be adopted in future work, and that the use of QSSA be abandoned.
The free energy–reaction coordinate profile for α‐chymotryptic hydrolysis of a series of N‐acetyl‐α‐L‐amino acid methyl esters
Authors: Martinek Karel , Klyosov A. A. , Kazanskaya N. F. , Berezin I. V. 
Published: January 2005

AbstractThe effect of added nucleophiles (methanol and 1,4‐butanediol) on the steady‐state kinetics of α‐chymotryptic hydrolysis of a series of N‐acetyl‐L‐amino acid methyl esters, R‐CH(NHCOCH3)C(O)OCH3, has been studied. As a result, the rate and equilibrium constants of the ‘elementary’ steps of the enzyme process have been determined.It has also been demonstrated how the free energy–reaction coordinate profile changes if the structure (the size of the hydrocarbon chain) of the ‘chemically inert’ substrate fragment R is varied. The effects observed can be described by the following equation:

equation image

where ΔGs and ΔGa are the free energies of formation of metastable intermediates, i.e., the enzyme–substrate complex and the acylenzyme, respectively, ΔG2≠ and ΔG3≠ are the free energies of activation for the chemical steps, i.e., enzyme acylation and acylenzyme hydrolysis, respectively; and ΔGtrans(R) is the free energy of transfer of substrate group R from water into a nonaqueous solvent.To explain the results obtained, a mechanism for enzyme–substrate interaction is suggested according to which the potential free energy of sorption of substrate group R on the enzyme is 2 ΔGtrans(R). Such a high gain in the free energy of hydrophobic interaction may only be realized if (a) in the free enzyme the sorption region has a thermodynamically unfavorable contact with the aqueous medium, and (b) water is forced out of the active center as a result of the hydrophobic interaction of substrate group R with the enzyme. Such a model is in agreement with the published x‐ray data on the structure of the crystalline enzyme.The kinetic experiment has proved that not all the potential free energy of sorption is realized as binding force. Thus the true free energy of the binding of substrate group R with the protein does not exceed half the maximum value, both in the enzyme–substrate complex and acylenzyme.
Yet another direct measurement of the rate constant for the recombination of methyl radicals
Authors: James F. C. , Simons J. P. 
Published: January 2005

AbstractThe decaying absorption of CH3 radicals at 216.4 nm has been followed over more than three half‐lives using a photoelectric split‐beam kinetic spectrometer. The rate constant for recombination kr was found to be (5.60 ± 0.76) × 10−11 cm3/molecule·s.
Chlorination of substituted phenols with chloramine T. A kinetic study
Authors: Balasubramanian V. , Thiagarajan V. 
Published: January 2005

AbstractKinetics of chlorination of substituted phenols with a particular emphasis on p‐nitrophenol (PNP) have been extensively studied using chloramine T (CAT). The effect of added mineral acids, neutral salts, and chloride have been investigated in detail. In aqueous acetic acid at high acidities the reactive phenols follow a zero‐order process, while PNP or the disubstituted derivatives give a fractional‐order dependence on substrate concentration. The concentration dependence of rate with respect to PNP, the chlorinating agent, and acid reveals the rate law

1/kobs versus 1/[PNP] gave a straight line with a finite intercept. In aqueous dimethylformamide (DMF) and dimethylsulfoxide (DMSO) the reaction shows a second‐order dependence on CAT and a first‐order dependence on PNP in the case of DMF and a slight increment in order in DMSO. Addition of water increases the rate both in aqueous acetic acid and in dipolar aprotic solvents such as DMF and DMSO. The order of the reaction with respect to CAT is found to be dependent on pH as well as the reactivity of the phenols. In buffered acetic acid medium a second‐order dependence on CAT was followed up to pH 7. The rate variations with temperature in the range of 30°¨Dot;50°C have been studied for all the substituted phenols, and the respective activation parameters have been calculated. The empirical rate law is accounted for by a mechanism involving species generated from CAT complexing PNP. Protonated CAT, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H}_{\rm 2} \mathop {\rm O}\limits^{\rm + } {\rm Cl} $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm Cl}\mathop {\rm O}\limits^{\rm + } {\rm AcH} $\end{document}, and dichloramine T (DCT) are considered important depending on reaction media. The effect of salts, pH, structural variations, and solvent dependence have been accounted for by the proposed mechanism. An attack by positive chlorine on oxygen of the phenol is the preferred mode of attack.
Radiation‐induced dehalogenation of 1,1,1,2 tetrachloroethane and 1,1,2 trichloro‐1 bromoethane reactions of 1,1,2 trichloroethyl radicals
Authors: Aloni R. , Katz M. G. , Rajbenbach L. A. 
Published: January 2005

AbstractThe kinetics of the radiation‐induced free radical chain reactions in solutions of CCl3CClH2 and CCl2BrCH2Cl in cyclohexane (RH) were studied in the temperature range of 90–225°C. 1,1,2 trichloroethyl and 1,1,1,2 tetrachloroethyl radicals were produced by the reaction of radiolytically generated cyclohexyl (R) radicals with solutes. The reactions studied were
equation image
The following rate expressins were obtained:

where θ = 2.303RT in kcal/mole. From the activation parameters of the k4/k5 rate constant ratio and the assumption that E4 = E, E5 was calculated to be 20.2 ± 0.2 kcal/mole. The Arrhenius parameters for the Cl atom elimination reaction from chloroethyl radicals derived from liquid and gas‐phase studies are compared.
The two‐parameter taft equation in kinetics of free radical reactions
Authors: Afanas'Ev I. B. 
Published: January 2005

AbstractA new method was developed for the calculation of the resonance substituent constants of the two‐parameter Taft equation logksub/k0=ρ*σ*+r*σr. It is based on a relationship between the spin density in free radicals and the rate constants of radical substitution reactions of CH3. Possibilities and limitations of the application of this correlation equation to the investigation of substitution and addition radical reactions are discussed.
Energy disposal in the three‐centered elimination of df from 1,1,2‐trifluoroethane‐1‐d1
Authors: Holmes B. E. , Setser D. W. , Pritchard G. O. 
Published: January 2005

AbstractThe chemical activation data for three‐ and four‐centered hydrogen fluoride elimination from CH2FCDF2have been analyzed to assign the energy released to the olefin fragment in the three‐centered process and to estimate the threshold energies for elimination channels. Based upon thecis–transisomerization rates of CHF = CHF, 78% of the total available energy was released to the olefin fragment for the αα channel. The analysis suggests the existence of an appreciable barrier (∼10 kcal/mole) for the reverse reaction, addition of the CH2FCF carbene to DF. The threshold energies for αα, αβ, and βα elimination from 1,1,2‐trifluoroethane‐1‐d1were assigned as 71, 68, and 68 kcal/mole, respectively. Analysis of the chemical activation data for 1,1,2,2,‐tetrafluoroethane, without distinguishing between the three‐ and four‐centered elimination channels, suggests a threshold energy of ∼75 kcal/mole.
Pyrolysis of dimethyl peroxide
Authors: Batt L. , McCulloch R. D. 
Published: January 2005

AbstractBy using isobutane (t‐BuH) as a radical trapit has been possible to study the initial step in the decomposition of dimethyl peroxide (DMP) over the temperature range of 110–140°C in a static system. For low concentrations of DMP (2.5 × 10−5−10−4M) and high pressures of t−BuH (∼0.9 atm) the first‐order homogeneous rate of formation of methanol (MeOH) is a direct measure of reaction (1): \documentclass{article}\pagestyle{empty}\begin{document}${\rm DMP}\mathop \to \limits^1 2{\rm Me}\mathop {\rm O}\limits^{\rm .},{\rm Me}\mathop {\rm O}\limits^{\rm .} + t{\rm - BuH}\mathop \to \limits^4 {\rm MeOH} + t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u}$\end{document}. For complete decomposition of DMP in t‐BuH, virtually all of the DMP is converted to MeOH. Thus DMP is a clean thermal source of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}. In the decomposition of pure DMP complications arise due to the H‐abstraction reactions of Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document} from DMP and the product CH2O. The rate constant for reaction (1) is given by k1 = 1015.5−37.0/θ sec−1, very similar to other dialkyl peroxides. The thermochemistry leads to the result D(MeOOMe) = 37.6 ± 0.2 kcal/mole and /H(Me\documentclass{article}\pagestyle{empty}\begin{document}$\mathop {\rm O}\limits^{\rm .}$\end{document}) = 3.8 ± 0.2 kcal/mole. It is concluded that D(ROOR) and D(ROH) are unaffected by the nature of R. From ΔS and A1, k2 is calculated to be 1010.3±0.5 M−1· sec−1: \documentclass{article}\pagestyle{empty}\begin{document}$2{\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^2 {\rm DMP}$\end{document}. For complete reaction, trace amounts of t‐BuOMe lead to the result k2 ∼ 109 M−1 ·sec−1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - Bu}\mathop \to \limits^5$\end{document} products. From the relationship k6 = 2(k2k5a)1/2 and with k5a = 108.4 M−1 · sec−1, we arrive at the result k6 = 109.7 M−1 · sec−1: \documentclass{article}\pagestyle{empty}\begin{document}$2t{\rm - u}\mathop {\rm B}\limits^{\rm .} \to (t{\rm - Bu)}_{\rm 2}{\rm,}t{\rm -}\mathop {\rm B}\limits^{\rm .} {\rm u} + {\rm Me}\mathop {\rm O}\limits^{\rm .} \mathop \to \limits^6 t{\rm - BuOMe}$\end{document}.
The SO2(3B1) photosensitized isomerization of cis‐ and trans‐1,2‐dichloroethylene
Authors: Wampler Fred B. , Böttenheim Jan W. 
Published: January 2005

AbstractThe photolysis of SO2 at 3712 Å in the presence of the 1,2‐dichloroethylenes has been investigated at 22deg;C. The data are consistent with the SO2(3B1) photosensitized isomerization of the 1,2‐dichloroethylene isomer. A kinetic treatment of the initial quantum yield data was consistent with the formation of a polarized charge‐transfer intermediate whenever SO2(3B1) molecules and one of the 1,2‐dichloroethylene isomers collide which ultimately decays unimolecularly to the cis‐isomer with a probability of 0.70 ± 0.26 and to the trans‐isomer with a 0.37 ± 0.16 probability. Quenching rate constants for removal of SO2(3B1) molecules by cis‐ and trans‐1,2‐dichloroethylene have been estimated from quantum yield data and from laser excited phosphorescence lifetimes using an excitation wavelength of 3130 Å. Estimates of the quenching rate constant (units of 1./mole ± sec) are for the cis‐isomer, (1.63 ± 0.71) × 1010, quantum yield data, and (2.44 ± 0.11) × 1010, lifetime data; and for the trans‐isomer,(2.59 ± 0.09)×1010, lifetime data, and (2.35 ±0.89) × 1010, quantum yield data. An experimentally determined photostationary composition,[cis‐C2Cl2H2]/[trans‐C2Cl2H2] = 1.8 ‐ 0.1, was in good agreement with a value of 2.00 ‐ 1.15 which was predicted from rate constants derived in this study.
Kinetics of the Diels–Alder addition of acrolein to cyclohexa‐1,3‐diene and its reverse reaction in the gas phase
Authors: Huybrechts G. , Paternoster G. , Baetens P. 
Published: January 2005

AbstractThe Diels–Alder addition of acrolein to cyclohexa‐1,3‐diene has been studied between 486 and 571°K at pressures ranging from 55 to 240 torr. The products are endo‐ and exo‐5‐formylbicyclo[2.2.2]oct‐2‐ene (endo‐ and exo‐FBO), and their formations are second order. The rate constants (in l./mole · sec) are given by

The retro‐Diels–Alder pyrolysis of endo‐FBO has also been studied. In the ranges of 565–638°K and 6–38 torr, the reaction is first order, and its rate constant (in sec−1) is given by

The reaction mechanism is discussed. The heat of formation and the entropy of endo‐FBO are estimated.
Abstraction of chlorine atoms from chloroalkanes. III. The kinetics of liquid phase reactions of trichlorosilyl radicals with chloromethanes
Authors: Aloni R. , Horowitz A. , Rajbenbach L. A. 
Published: January 2005

AbstractThe kinetics of chlorine atom abstraction from the chloromethanes (ClM), CCl4, CHCl3, CH2Cl2, and CH3Cl by radiolytically generated trichlorosilyl radicals was studied in the liquid phase by a competitive method. Arrhenius parameters of chlorine atom abstraction from chloromethanes relative to that of bromine atom abstraction from cyclohexyl bromide (RBr) were as follows:
equation image
The error limits are two standard deviations (2σ) from least mean square Arrhenius plots. From the linear correlation between Ecl values derived from the reactions of SiCl3 and cyclohexyl radicals with the ClM series it is estimated that Ecl (R + CH3Cl) ≃ 16 kcal/mole. In addition the relative Arrhenius parameters for the hydrogen atom abstraction from SiHCl3 and chlorine atom abstraction from CCl4 by cyclohexyl radicals were obtained log AH/Acl = 0.12 ± 0.15 and EH − Ecl = 0.24 ± 0.26. The EH − Ecl value was combined with existing data on E(R + CCl4) to yield the EH(R + SiHCl3) value.
Quenching rate constants for the removal of SO2(3B1) by various fluorinated olefins
Authors: Wampler Fred B. 
Published: January 2005

AbstractA competitive technique employing the SO2(3B1) photosensitized isomerization of cis‐C2F2H2 to trans‐C2F2H2 in the presence of selected fluorinated olefins has been used at 3712 Å and 22°C to determine the quenching rate constants of the reaction \documentclass{article}\pagestyle{empty}\begin{document}${\rm SO}_{\rm 2} ({}^3B_1){\rm M}\mathop \to \limits^{k_{_4}}$\end{document} removal. With PSo2 = 25.4 torr and Pcis‐C2F2H2 = 0.239 torr Stern–Volmer plots for M = C2H4, C2H2F, 1,1‐C2F2H2, C2F4, and C3F6 yielded k4 (units of 1010 l./mole · sec) values of 5.29 ± 0.16, 4.21 ± 0.53, 1.92 ± 0.23, 0.575 ± 0.060, and 0.0335 ± 0.0027, respectively. The results were consistent with the ability of an olefin to quench SO2(3B1) being inversely proportional to the polarizability of the olefin's π bond and the effect can be clearly noted as each H atom in C2H4 is individually replaced by an F atom.