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Showing papers on "Elementary reaction published in 1980"


Journal ArticleDOI
TL;DR: In this paper, an extensive reaction set has been used to probe the sensitivity of the H2-O2 system in a wide pressure-temperature range, and the results indicate the present model to be useful over a wide range of pressure and temperature.
Abstract: Kinetic modeling calculations on the H2–O2 system have been carried out with an extensive reaction set to probe the vicinity of the three explosion limits. Sensitivity analysis is used throughout this investigation to study system behavior, in particular, to elucidate mechanistic details. The concentrations and sensitivity profiles are discussed in light of the appropriate experimental results and existing theories of hydrogen combustion. The results indicate the present model to be useful over a wide pressure–temperature range. The reaction set is also used to probe the sensitivities for an experimental study designed to measure the rate constant of an important elementary reaction, H+O2+M→HO2+M, involved in this system. The versatility of the reaction set is also demonstrated by a study of a related chemical reaction, the decomposition of hydrogen peroxide. Finally, prospects for utilizing the methods and results of this study to examine other complex kinetic schemes are discussed.

100 citations


Journal ArticleDOI
TL;DR: In this article, the results of a pulse-irradiation with high energy electrons and the changes in optical absorption and conductivity were recorded in the micro-second to second range.

80 citations


Journal ArticleDOI
TL;DR: In this article, the authors treated chemical reactions in the solid phase as radiationless electronic transitions in which the rapprochement of the reactants due to intermolecular vibrations was taken into account together with the quantum motion along the reaction coordinate.

69 citations


Journal ArticleDOI
TL;DR: In this article, it is shown that it is possible to determine the true kinetics of each single reaction which is progressing within the multiple reductions; this is done with the use of a reactional triangle depending only on the kind of the multiple reaction which was taken into account.

47 citations


Journal Article
01 Jan 1980-JAMA
TL;DR: A peculiar facial flushing and tachycardia occurring two to three days after discharge and within a few minutes after drinking one or two glasses of beer is noted.
Abstract: To the Editor.— The disulfiram reaction to ethanol usually lasts a couple of hours and is characterized by a flushed face and a feeling of warmth. Often nausea, vomiting, sweating, and headaches occur. Rarely, hypotension, syncope, vertigo, or chest pains develop. Besides disulfiram, these reactions are known to occur after chlorpropamide, where the tendency to flush after alcohol appears to be inherited as an autosomal dominant trait.1The antiprotozoal agent, metronidazole, may cause similar reactions. Cefoperazone is a new semisynthetic parenteral cephalosporin. We recently administered cefoperazone to 24 healthy male volunteers as part of a tolerance-kinetics study. After a week of infusions, several of the subjects noted a peculiar facial flushing and tachycardia (to 180 beats per minute) occurring two to three days after discharge and within a few minutes after drinking one or two glasses of beer. We then deliberately challenged five other subjects 36 hours after their

36 citations


Journal ArticleDOI
TL;DR: In this paper, the photo-smiles rearrangement reaction of N-[p-nitrophenoxy)alkyl]aniline was studied by measuring the absorption spectra of transient species.
Abstract: Photo-Smiles rearrangement reaction of N-[ω-(p-nitrophenoxy)alkyl]aniline was studied by measuring the absorption spectra of transient species. Two intermediates A and B were observed and were assigned to a solvated ion pair and the Meisenheimer complex, respectively. The reaction scheme, starting material→intramolecular charge transfer on excitation→A→B→final product, was derived from the relative yields and lifetimes of A and B as well as from the effects of solvent polarity, of triethylamine and oxygen, and of the alkyl chain length on each step of reaction.

32 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the kinetics of primary and secondary processes in the overall reaction of H 2S atoms with NF2 radicals from 298 to 550 K and derived the rate constants for the following elementary reactions.
Abstract: Atomic resonance absorption in the far vacuum ultraviolet and atomic resonance fluorescence have been used to investigate the kinetics of primary and secondary processes in the overall reaction of H 2S atoms with NF2 radicals from 298 to 550 K. Rate constants for the following elementary reactions have been determined directly [k298/cm3 molecule–1 s–1(1 σ)]: H + NF2 [graphic omitted] HF + NF; k1=(1.5 ± 0.2)× 10–11; O + NF2 [graphic omitted] NF + FO; k5=(1.8 ± 0.9)× 10–12; N + NF2 [graphic omitted] NF + NF; k8=(3.0 ± 1.2)× 10–12.The overall H + NF2 reactive system, containing H2, is characterised as a self-propagating chain reaction, in which the chain carriers are H, NF and F. Ground-state N 4S atoms are formed by the reaction H + NF, although these atoms play only a minor role in propagating the overall H + NF2 chain reaction. Computer modelling of the H and N atom profiles was used to obtain values for k4 and k2: H + NF [graphic omitted] HF + N; k4=(2.5 ± 0.5)× 10–13; NF + NF [graphic omitted] N2+ 2F; k2=(7.0 ± 3.5)× 10–11. Thus, the predominant decay channel for NF radicals is through rapid bimolecular disproportionation to give N2+ 2F.

28 citations


Book ChapterDOI
TL;DR: In this article, a detailed review of the kinetics and mechanisms of free radical oxidation of alkanes and alkenes in the liquid phase is presented, as well as the techniques for their measurement and determination under mild conditions.
Abstract: Publisher Summary This chapter reviews the kinetics and mechanisms of free radical oxidation of alkanes and alkenes in the liquid phase, and presents the techniques for their measurement and determination under mild conditions in the liquid phase. The chapter focuses on both the kinetics and product formation as diagnostic tools for elucidating the detailed mechanisms of oxidation reactions in terms of elementary steps, rate coefficients, thermochemistry, and structure reactivity relationships. The chapter discusses the relationships, exemplified by reactions of simple molecules and the way in which they may be used to interpret and predict the rates and products of oxidation reactions involving more complex molecules or extreme conditions. The evaluation of absolute rate coefficients of elementary reactions is one of the most important steps in the kinetic analysis. Comparison of such values with the general chemical knowledge of radical reactions serves first as a check on the kinetic analysis and second, if shown to be reliable, it may be used in the kinetic analysis of other systems.

25 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the energy partitioning quotient of an intramolecular substitution reaction and showed that the fraction of the reverse activation energy is released as kinetic energy.
Abstract: The loss of substituents X from molecular ions of ortho substituted 2-benzoyl pyridines has been investigated as a function of the dissociation energy of the C-X bond. Comparison of unimolecular and collisional induced decompositions of the resulting [M- XI' ions and reference ions arising from 3-hydroxypyrido[l,2alindole shows that cyclic fragment ions are formed in every case by an intramolecular substitution reaction with the exception of the parent compound (X=H), which gives rise to a mixture of [M-HI' ions with different structures. The heat of formation of the cyclic ion has been estimated experimentally and by calculation using thennochemical data, and from this value and the appearance energies, the activation energies of the reverse reactions have been evaluated for the different reaction systems. Measurement of the kinetic energy release during the substitution readions shows that only part of the reverse activation energy is released as kinetic energy. The energy partitioning quotient varies from 0.37 to 0.08 depending on the dissociation energy of the C-X bond or the reaction enthalpy. A sudden change in the energy partitioning quotient is observed with increasing exothermicity of the reaction, paralleling the behaviour of similar reaction systems. These results are interpreted as a demonstration of the influence of the variation of transition state position on the energy partitioning quotient. It has been shown recently2 that the partitioning of the excess potential energy of the transition states (or the activation energy of the reverse reactions F:) between the kinetic energy T, released during the reaction, and the internal energy F* of the products during the loss of ortho substituents from the molecular ions of substituted benz.alacetones depends strongly and systematically on the thermochemistry of the reaction or the position3 of the transition state on the reaction coordinate. Thus it appears that an investigation of the variation of the kinetic energy release and the energy partitioning quotient q = T/&f with structural changes of the reactant ions gives some insight into fundamental properties of elementary reactions of organic ions, which will be useful in testing mechanistic models of organic chemistry and linking them more closely to physical theories of chemical reactions. The loss of substituents from molecular ions of benzalacetones with formation of 2-rnethylbenzpyrylium ions4 can be regarded as an intramolecular aromatic substitution reaction,5 a well known reaction in organic chemistry. As a further example of this type of reaction the results of a detailed investigation of the loss of ortho substituents from the molecular ions of substituted 2-benzoyl pyridines la-lg (Scheme 1) are reported. The decomposition of the molecular ions of la-lg occurs by the three competing fragmentation pathways A-C shown in Scheme 1. Compound la exhibits large peaks due to [M-HI' and [M-CO]" ions in its 70eV mass spectrum, which are absent or of much lower relative abundance in the 70 eV mass spectra of

20 citations


Journal ArticleDOI
TL;DR: A detailed analysis of the products formed when small amounts of pentane are added to slowly reacting mixtures of H2+ O2 at 480 °C was made in this article. But this analysis was performed with only three species of pentyl radicals: pent-1-yl, pent-2-yl and pent-3-yl.
Abstract: A detailed analysis has been made of the products formed when small amounts of pentane are added to slowly reacting mixtures of H2+ O2 at 480 °C. Use of the rate constants for attack of H, O, OH and HO2 at specific C—H bonds in pentane enables the proportion of pent-1-yl, pent-2-yl and pent-3-yl radicals to be calculated for all mixtures studied. Use of a wide range of H2 and, particularly, of O2(8–355 Torr) pressures makes it possible to confirm suggested mechanisms for the oxidation of each of the three species of pentyl radical. Rate constants have been obtained for a large number of the elementary reactions involved, almost all of which have not been determined previously. The values of the rate constants form a very consistent pattern with those determined from studies with the C2–C4 alkanes and neopentane as additive.

19 citations


Journal ArticleDOI
TL;DR: In this article, the gas phase free radical displacement reaction has been studied in the temperature range of 240-290°C and at 140°C with the thermal decomposition of azomethane (AM) and di-tert-butylperoxide (DTBP), respectively, as methyl radical sources.
Abstract: The gas-phase free radical displacement reaction has been studied in the temperature range of 240–290°C and at 140°C with the thermal decomposition of azomethane (AM) and di-tert-butylperoxide (DTBP), respectively, as methyl radical sources. The reaction products of the CD3 radicals were analyzed by mass spectrometry. Assuming negligible isotope effects, Arrhenius parameters for the elementary radical addition reaction were derived: The data are discussed with respect to the back reaction and general features of elementary addition reactions.

Journal ArticleDOI
TL;DR: In this paper, a reaction model for pyrolysis of ethylbenzene and n-hexane, and CO oxidation is presented, based on a reduction of the complete set of elementary reactions.
Abstract: Modern digital methods and powerful computers make it possible to simulate the time behavior of chemical reactions. These calculations can be performed on systems containing an almost unlimited number of elementary reactions. Generally, however, the reaction models used should contain only those elementary reactions which describe the bulk of the conversion. Such a reaction model may be obtained by reduction of the complete set of elementary reactions. Another possibility is analysis of the chemical system starting from conditions ensuring a simple chemistry, which is generally the case at low temperatures and low conversions. The reaction model may then be extended into the range of the reaction variables (temperature, time) of interest. Mathematical simulations may be helpful during the development of the reaction model, and sometimes even decisive. These methods were applied to the pyrolysis of ethylbenzene and n-hexane, and to CO oxidation. They yield information on the reaction paths, the importance of particular elementary reactions, and reaction stability. Furthermore, quantitative data can be obtained concerning the influence of single elementary reactions on the product distribution. The sensitivity matrix shows, e.g., whether the determination of kinetic parameters of an elementary reaction from kinetic data of the overall reaction is possible in principle, and how high the accuracy of the rate constants should be for simulation of the reaction. Both results are important for modeling chemical reactions.

Journal ArticleDOI
TL;DR: In this article, the authors derived an equation for the redistribution of isotopic molecules in an elementary reaction based on atom distribution matrices, and proved that it is possible to compute the equation on the basis of the atom distribution matrix.
Abstract: Kinetic equations for the redistribution of isotopic molecules in an elementary reaction have been derived on the basis of atom distribution matrices.

Journal ArticleDOI
TL;DR: In this article, a matrix of distribution and transfer of atoms (MDA and MTA) and their adequate bigraphs are introduced, and several types of mechanisms specified by different MDA's, which can be determined by labeling methods, are possible for one elementary reaction.
Abstract: Elementary reactions are considered to result from transitions of the initial species to the final atomic groups. Matrices of distribution and transfer of atoms (MDA and MTA, respectively) and their adequate bigraphs are introduced. Several types of mechanisms specified by different MDA's, which can be determined by labelling methods, are possible for one elementary reaction.

Book ChapterDOI
Russell W. Maatman1
TL;DR: In this article, the authors considered the rate-determining step in a solid-catalyzed gas reaction when only one molecule reacts and showed that surface mobility is a factor in desorption.
Abstract: Publisher Summary In a solid-catalyzed gas reaction any one of several steps may be a rate-determining step The possibilities should be considered when only one molecule reacts The rate-determining step could be adsorption, reaction on the surface after adsorption, or desorption The dissociation of the molecule might or might not necessarily accompany adsorption A surface reaction might be one of several kinds The adsorbed molecule could isomerize or decompose on a fixed site, and either kind of step could be rate determining In some cases reaction occurs only when two adsorbed molecules react with each other Regardless of whether the surface reaction is monomolecular or bimolecular, the reacting molecules could possess surface mobility and not be attached to fixed sites A desorption rate-determining step could be simple desorption from a site upon which reaction has occurred Surface mobility could also be a factor in desorption For example, in some cases the adsorbed molecule must move from the site of reaction to a site from which it can desorb

Journal ArticleDOI
TL;DR: In this paper, an analysis of the thermal uncatalyzed reaction of a homogeneous mixture of steam and methane for the production of hydrogen on the basis of detailed chemical kinetics is presented.

Journal ArticleDOI
TL;DR: In this article, an extensive reaction set has been used to probe the sensitivity of the H2-O2 system in a wide pressure-temperature range, and the results indicate the present model to be useful over a wide range of pressure and temperature.
Abstract: Kinetic modeling calculations on the H2–O2 system have been carried out with an extensive reaction set to probe the vicinity of the three explosion limits. Sensitivity analysis is used throughout this investigation to study system behavior, in particular, to elucidate mechanistic details. The concentrations and sensitivity profiles are discussed in light of the appropriate experimental results and existing theories of hydrogen combustion. The results indicate the present model to be useful over a wide pressure–temperature range. The reaction set is also used to probe the sensitivities for an experimental study designed to measure the rate constant of an important elementary reaction, H+O2+M→HO2+M, involved in this system. The versatility of the reaction set is also demonstrated by a study of a related chemical reaction, the decomposition of hydrogen peroxide. Finally, prospects for utilizing the methods and results of this study to examine other complex kinetic schemes are discussed.

Journal ArticleDOI
TL;DR: In this paper, a principle of quasistationarity in the isotopic kinetics has been formulated for a system with one elementary reaction, and the principle has been shown to hold for the case of a single reaction.
Abstract: Kinetic equations of the isotopic exchange in a system with one elementary reaction have been derived. A principle of quasistationarity in the isotopic kinetics has been formulated.

Journal ArticleDOI
TL;DR: On the basis of matrices of transfer of atoms kinetic equations of isotope transfer between the components participating in elementary reactions have been derived in this article, where the authors show that the matrices can be expressed as
Abstract: On the basis of matrices of transfer of atoms kinetic equations of isotope transfer between the components participating in elementary reactions have been derived.

Journal ArticleDOI
TL;DR: In this paper, a linear relationship between log10K D and log 10Kp was found, where Kp was the association constant of phenol with ethers, and the mechanism was based on the activation enthalpy of elementary reaction and it was concluded that the main factor governing the reaction was the extent of activation of the protonated oxirane.

Journal ArticleDOI
01 Sep 1980-Polymer
TL;DR: In this paper, the effect of hydroxyl groups of various phenols on the course of the reaction of their alkali metal salts with epichlorohydrin in dipolar, aprotic solvents has been studied.

Journal ArticleDOI
01 Dec 1980
TL;DR: In this paper, the effect of a resonant optical field on chemical equilibrium and on uni-and bimolecular chemical reaction kinetics is studied, in particular, the relationship between steady-state concentrations of reactants in a quasicontinuous light pulse field, that is, the generalized mass action law.
Abstract: On the basis of a consistent set of photochemical kinetic equations previously obtained by the authors the effect of a resonant optical field on chemical equilibrium and on uni- and bimolecular chemical reaction kinetics is studied. We established, in particular, the relationship between steady-state concentrations of reactants in a quasicontinuous light pulse field, that is, the generalized mass action law. Dependences of reaction product yields on the intensity of coherent light were found, also the relationships between effective reaction rare constants and coherent optical field parameters as well as relaxation interactions. The results are compared with those obtained from a phenomenological description widely used in pratical photochemistry, based on elementary kinetics equations of balance type for reactant concentrations. It is shown that photochemical processes is coherent optical fields cannot be described correctly by rate (or balance) equations.

Book ChapterDOI
01 Jan 1980
TL;DR: In this article, the authors investigated the general behavior of the temperature dependence of elementary bimolecular reactions, considering both equilibrium and non-equilibrium effects on the kinetics, and found that both positive and negative deviations from the Arrhenius law can occur, depending on the system parameters.
Abstract: There is now evidence that the Arrhenius plots of several elementary bimolecular reactions show substantial deviations from linearity when studied over a wide temperature range. If such deviations are widespread, they can cause serious difficulties in extrapolating low temperature kinetic data for use in theoretical studies of explosions. Accordingly, we have investigated the general behavior of the temperature dependence of elementary bimolecular reactions, considering both equilibrium and non-equilibrium effects on the kinetics. The activated complex theory model was used to explore equilibrium kinetic behavior. The essential factor in determining deviations from the Arrhenius law is shown to be the interconversion of translational, rotational, and vibrational degrees of freedom that takes place when two reactant molecules come together to form the activated complex. This leads to two effects, (i) in general the measured Arrhenius activation energy EA will be different from the barrier height E0 for the reaction, and (ii) the value of EA itself may be a function of T in which case the reaction will have a non-linear Arrhenius plot if studied over a large temperature range. Both positive and negative deviations from the Arrhenius law are shown to be possible, and the factors which influence this behavior are investigated. Non-equilibrium effects are investigated, using a collisional model. Again it is found that both positive and negative deviations from the Arrhenius law can occur, depending on the system parameters.

Book ChapterDOI
01 Jan 1980
TL;DR: The high reactivity of radicals makes it extremely difficult to study individual, elementary reaction steps by conventional experimental techniques and there are very often a number of competing reaction pathways which sometimes lead to ambiguous, in some cases even contradictive, interpretations of the obtained results as discussed by the authors.
Abstract: The high reactivity of radicals makes it extremely difficult to study individual, elementary reaction steps by conventional experimental techniques There are very often a number of competing reaction pathways which sometimes lead to ambiguous, in some cases even contradictive, interpretations of the obtained results

Journal ArticleDOI
TL;DR: The kinetics of an elementary reaction step are discussed from the viewpoint of the stochastic theory of chemical kinetics, and the general form of the rate constant found in the Stochastic approach is described and compared with the expression from transition state theory.

Journal ArticleDOI
TL;DR: In this article, a reaction model for pyrolysis of ethylbenzene and n-hexane, and CO oxidation is presented, based on a reduction of the complete set of elementary reactions.
Abstract: Modern digital methods and powerful computers make it possible to simulate the time behavior of chemical reactions. These calculations can be performed on systems containing an almost unlimited number of elementary reactions. Generally, however, the reaction models used should contain only those elementary reactions which describe the bulk of the conversion. Such a reaction model may be obtained by reduction of the complete set of elementary reactions. Another possibility is analysis of the chemical system starting from conditions ensuring a simple chemistry, which is generally the case at low temperatures and low conversions. The reaction model may then be extended into the range of the reaction variables (temperature, time) of interest. Mathematical simulations may be helpful during the development of the reaction model, and sometimes even decisive. These methods were applied to the pyrolysis of ethylbenzene and n-hexane, and to CO oxidation. They yield information on the reaction paths, the importance of particular elementary reactions, and reaction stability. Furthermore, quantitative data can be obtained concerning the influence of single elementary reactions on the product distribution. The sensitivity matrix shows, e.g., whether the determination of kinetic parameters of an elementary reaction from kinetic data of the overall reaction is possible in principle, and how high the accuracy of the rate constants should be for simulation of the reaction. Both results are important for modeling chemical reactions.

Book ChapterDOI
01 Jan 1980
TL;DR: The results of the quantum-chemical investigation of the radiation-induced polymerization in crystals are presented in this article, where the main elementary reaction steps are detected, giving a reasonable interpretation of the kinetic data, and the basic conclusion is that the propagation reaction involving the growing polymer ion to the monomer molecule placed at a lattice point needs no activation energy.
Abstract: The results of the quantum-chemical investigation of the radiation-induced polymerization in crystals are presented The main elementary reaction steps are detected, giving a reasonable interpretation of the kinetic data The basic conclusion is that the propagation reaction involving the addition of the growing polymer ion to the monomer molecule placed at a lattice point needs no activation energy The experimentally observed activation energy is attributed to conformational processes involved in the termination stage

Book ChapterDOI
01 Jan 1980
TL;DR: In this paper, the results of microscopic and macroscopic experiments on elementary bimolecular reactions and the relationship between various quantities that have been defined during this process are established, including the classical energy barrier to reaction, the difference between the zero-point quantum levels of reactants and the activated state, the threshold energy, and the activation energy.
Abstract: Publisher Summary When chemical change occurs, it usually does so through a network of interacting steps known as the reaction mechanism. The identification of mechanism in this sense is one of two major problems in the field of chemical kinetics. The other is to investigate and attempt to understand the details of chemical reactions that cannot be further subdivided into the processes of lesser molecular complexity. These processes, which necessarily involve the participation of a small integral number of molecules, are termed elementary reactions and they can be studied in greatest detail in the gas phase. This chapter describes the results of microscopic and macroscopic experiments on elementary bimolecular reactions and on establishing the relationship between various quantities that have been defined during this process. In these experiments, four interrelated energy quantities are considered: the classical energy barrier to reaction, the difference between the zero-point quantum levels of reactants and the activated state, the threshold energy, and the activation energy. Despite the connection between them, these quantities are neither conceptually nor usually quantitatively the same and therefore, the terms are used with care.

Journal ArticleDOI
TL;DR: In this article, the general equations and the solution procedure for predicting the temperature and the species concentration of a reacting mixture of hydrogen and oxygen in a well-s stirred reactor are described and a method of solution for calculation of the sensitivity or the importance of elementary reactions are given.

01 Jan 1980
TL;DR: The results of the quantum-chemical investigation of the radiation-induced polymerization in crystals are presented in this paper, where the main elementary reaction steps are defined, giving a reasonable interpretation of the kinetic data.
Abstract: The results of the quantum-chemical investigation of the radiation-induced polymerization in crystals are presented. The main elementary reaction steps are de­ tected, giving a reasonable interpretation of the kinetic data. The basic conclusion is that the pro~a­ gat ion reaction involving the addition of the grow1n~ polymer ion to the monomer molecule placed at a latt1ce point needs no activation energy. The experimental­ ly observed activation energy is attributed to conformational processes involved in the termination stage.