Showing papers on "Elementary reaction published in 1972"
TL;DR: In this paper, the cage radius and diffusion coefficient of polyethylene and polymethyl methacrylate are calculated from the viewpoint of Waite's cage diffusion theory and Levedev's model, showing that the diffusion coefficient is in the range 10−16 to 10−18 cm2 s−1.
Abstract: Kinetic laws and particularities of migration mechanisms of free valence in the processes of decay of free radicals in polymers are dealt with. The basic examples correspond to the results for polyethylene and polymethyl methacrylate. The kinetics of the decay reactions are discussed from the viewpoint of Waite's cage diffusion theory and Levedev's model. From the kinetic data of various authors the cage radius and diffusion coefficient are calculated. With increasing temperature the cage radius in polyethylene increases from 5.3a (120°K) to 40–60 a (360°K) and it has to be looked upon as an effective kinetic parameter. The diffusion coefficient corresponding to free valence displacement at long distances is in the range 10−16 to 10−18 cm2 s−1. In amorphous polymers at temperatures exceeding the glass temperature diffusion proves to be of major importance for long-distance migration. In a series of other examples, chemical reactions play a more important role, such as hydrogen atom transfer and radical decomposition. Results of measurement of the corresponding elementary reaction compared with the rate constants of decay are mentioned. Under real conditions, migration is affected simultaneously by both diffusion and chemical mechanisms.
36 citations
25 citations
01 Jan 1972
TL;DR: The use of tandem mass spectrometers as an experimental tool and the type of information derived from such studies are closely related to the crossed-beam studies of these reactions discussed by Herman and Wolfgang in Chapter 12, to the charge exchange studies Lindholm discussed in Chapter 10, and to the ion cyclotron resonance technique described by Henis in Chapter 9 as mentioned in this paper.
Abstract: The use of tandem mass spectrometers as an experimental tool and the type of information derived from such studies are closely related to the crossed-beam studies of these reactions discussed by Herman and Wolfgang in Chapter 12, to the charge-exchange studies Lindholm discussed in Chapter 10, and to the ion cyclotron resonance technique described by Henis in Chapter 9. The relationship of these techniques is illustrated by Fig. 1, which shows a highly sophisticated, idealized apparatus suitable for studying all these problems. All four approaches have the characteristic that, with appropriate care, one can isolate a particular elementary reaction and study it without interference from the many complex, interacting parameters present in a system which does not involve some method of species selection.
9 citations
TL;DR: In this article, a special curvilinear coordinate system is introduced, coinciding with the normal vibrational modes of reactants or products in the asymptotic regions and describing their gradual transformation along the reaction coordinate.
Abstract: The probabilities of bimolecular chemical reactions are studied, taking account of vibrational transitions. A special curvilinear coordinate system is introduced, coinciding with the normal vibrational modes of reactants or products in the asymptotic regions and describing their gradual transformation along the reaction coordinate. It provides a generalization of a two-dimensional ‘natural collision coordinate system’ introduced by Marcus. In terms of these coordinates a model hamiltonian is defined, neglecting the curvature of the reaction coordinate and with a special potential, for which an exact adiabatic solution is found. Using its eigenfunctions as a basic, the Born perturbation expansion is given, being capable of treating vibrational transitions in the course of the elementary reaction act and including the curvature as a perturbation. The zero-order adiabatic hamiltonian is in fact that of the activated complex theory.
8 citations
TL;DR: In this paper, the reaction of two solid phases X and Y to give a solid compound XYv is taken as an example for the discussion of transport mechanisms and reaction steps, and the following methods of investigation are discussed: determination of the rate law, marker experiments, and calculation of the reaction rate.
Abstract: The reaction of two solid phases X and Y to give a solid compound XYv is taken as an example for the discussion of transport mechanisms and reaction steps. The following methods of investigation are discussed: determination of the rate law, marker experiments, and calculation of the reaction rate. It is pointed out that the investigation of powder reactions leads to problematic conclusions.
6 citations
TL;DR: First-order kinetics will be observed for mechanisms in which the labeled molecules enter the reaction with a molecularity of unity in elementary reaction steps if the molecularity with respect to labeled compounds is greater than unity, then the reaction need not appear first order.
6 citations
TL;DR: In this article, a shock tube coupled to a time-of-flight mass spectrometer has been used to study the reactions of ethyl radicals at temperatures much higher than before.
Abstract: A shock tube coupled to a time‐of‐flight mass spectrometer has been used to study the reactions of ethyl radicals at temperatures much higher than before. The radicals were formed by heating mixtures containing azoethane highly diluted in neon to between 1000 and 1540°K in reflected shock waves at a total density of 9×1017 particle/cc. Detailed measurements of the products including ethylene, acetylene, ethane, methane, propane, n‐butane, and methyl radicals have been made over a reaction time of 250 μsec. The effects of adding ethylene and azomethane to the reaction mixture have also been investigated. Experiments have been made on the thermal decomposition of n‐butane over the range 1160–1550°K, and the ``apparent first‐order'' decay rates for n‐butane yielded an activation energy of close to 32.5 kcal/mole. Possible mechanisms for product formation are qualitatively discussed and a set of 12 elementary reactions is adopted to describe the experimental observations.
6 citations
01 Jan 1972
TL;DR: In this paper, the structure of a reactant ion cannot be determined directly in the mass spectrometer, but it can be inferred by correlating appearance potentials or measured reaction rates with the properties of known structure.
Abstract: In kinetic studies of free-radical reactions, which are largely based on information obtained from end-product analysis, the structures of the free radicals formed in a given system are generally well established, and the rate constants measured for elementary reactions can be unambiguously ascribed to a well-characterized reactant radical. In contrast, kinetic studies of the reactions of hydrocarbon ions have generally been carried out in the mass spectrometer, where the structure of a reactant ion cannot be determined directly. Although numerous attempts have been made to derive information about ionic structures by correlating mass spectrometric information such as appearance potentials or measured reaction rates with the properties of ions of known structure (techniques which will be described in detail below), there are few cases where the structures of reactant hydrocarbon ions have been unambiguously established in the mass spectrometer. The problem is complicated by the well-known tendency of ions to isomerize. Thus, the propyl ions formed in the fragmentation of n-butane parent ions cannot be assumed to have the n-propyl structure, but may have several structures; in contrast, the propyl radicals formed in the pyrolytic fragmentation of n-butane are known to have the n-propyl structure. Furthermore, the relative abundances of the various isomers will depend on the energy deposited in the ions. This means that the composition of the isomeric reactant ions will vary with temperature and with pressure (since the extent of collisional deactivation of the excited precursors of certain isomer ions will vary with pressure) and with the ionizing energy.
4 citations
01 Jan 1972
TL;DR: For a single-step reaction occurring in isolation and at constant temperature, the rate of the reaction decreases as the reaction proceeds, due to the decrease in the active masses of the reactants as mentioned in this paper.
Abstract: Chemical kinetics is the study of the rates at which reactions proceed, and the mechanisms by which the overall changes occur. The term “active mass” is used to describe the amount of the particular reactant, which is able to take part in the reaction. If the reactants A, B and C all exist in the same phase, gas, liquid or solution, the total amount of each is able to react, but if they are not in the same phase, this is not so. For a single-step reaction occurring in isolation and at constant temperature, the rate of the reaction decreases as the reaction proceeds, due to the decrease in the active masses of the reactants. The manner of the variation of the rate with time depends on the number of atoms, molecules or ions involved in the bond rearrangement. This number is known as the molecularity of the reaction.
2 citations
TL;DR: In this article, a kinetic study on the reaction of 3-naphthyloxy) -2-hydroxy-1-propyl tosylate with excess isopropylamine in various solvents was studied, and using an analogue computer, the apparent first-order rate constants of elementary reactions in two possible paths (the direct substitution reaction of the tosyl group in (1) by the amino group in(2) [path 1], and the ring-closing reaction to form an epoxide and subsequent ring-opening reaction by the amine
Abstract: A kinetic study on the reaction of 3- (1-naphthyloxy) -2-hydroxy-1-propyl tosylate (1) with excess isopropylamine (2) in various solvents was studied, and using an analogue computer, the apparent first-order rate constants of elementary reactions in two possible paths (the direct substitution reaction of the tosyl group in (1) by the amino group in (2) [path 1], and the ring-closing reaction to form an epoxide and subsequent ring-opening reaction by the amine (2) [path 2]) were caluculated.Our results showed that the reaction pathway depends upon the solvent used. In nonpolar solvents such as cyclohexane and benzene, the reaction proceeds mainly by direct substitution [path 1], and in polar solvents such as pyridine and acetonitrile the ratio of path 2 to path 1 becomes large. In ethanol, a protic solvent, the reaction proceeds almost completely via an epoxide [path 2].
2 citations
TL;DR: In this article, the authors studied the thermal decomposition of 2-pentene in a flow apparatus under an atmospheric pressure, at temperatures ranging from 480 to 730°C, and with'residence times from 0.05 to 35 sec and nitrogen/2-pentenes mole ratios 6 and 15.575 T'.
Abstract: Thermal decomposition of 2-pentene was studied in a flow apparatus under an atmospheric pressure, at temperatures ranging from 480 to 730°C, and with 'residence times from 0.05 to 35 sec and nitrogen/2-pentene mole ratios 6 and 15. The overall reaction obeys the first order rate equation with the rate constant being log k (sec-1)=12.3-53000/4.575 T. The main reaction products were approximately equimolar amounts of methane and butadiene, consisting 50∼60 mol% of 2-pentene decomposed. Other reaction products were hydrogen, ethylene, ethane, propene, 1-butene, 2-butene, 1, 3-pentadiene, 3-methyl-1-butene and 4-methyl-2-pentene.The reaction can be accounted for by a free-radical chain process with complication due to competition between decomposition and isomerization of alkenyl as well as alkyl radicals. Ex- perimentally observed product distributions as well as reaction rates are found to be in good agreement with those calculated on the basis of estimated kinetic parameters of the elementary reactions in the proposed chain scheme.
TL;DR: In this paper, a simple method for the study of fast reactions of atoms with molecules using an ESR spectrometer was proposed, and a preliminary measurement was made of the rate constant for the reaction O+NO2=NO+O2.
Abstract: 1.
A simple method is proposed for the study of the kinetics of fast reactions of atoms with molecules using an ESR spectrometer.
2.
The theory of an integral diffusion method for the measurement of rate constants of elementary reactions was developed.
3.
A preliminary measurement was made of the rate constant for the reaction O+NO2=NO+O2.
TL;DR: In this article, the conditions under which the dependence of the chemical reaction rate on time acquires an exponential nature were determined, free from the requirement that the initial concentrations of X-atoms and X2 molecules should be close to their equilibrium values for the rate constant.
Abstract: The establishment of equilibrium in the chemical reaction X2+M ⇄ ⇄ 2X+M is examined. All possible transitions between the vibrational levels and the continuous spectrum are considered. Taking account of two relaxation times, an expression is obtained for the concentration of the X atoms and the chemical reaction rate as a function of time. The conditions under which the dependence of the chemical reaction rate on time acquires an exponential nature are determined. An expression free from the requirement that the initial concentrations of X-atoms and X2 molecules should be close to their equilibrium values is obtained for the rate constant.
TL;DR: In this article, the errors in determining the rate constants of elementary reactions that arise when quadratic rather than compound (simultaneous bi-and monomolecular) chain termination is assumed.
Abstract: We analyze the errors in determining the rate constants of elementary reactions that arise when quadratic rather than compound (simultaneous bi- and monomolecular) chain termination is assumed. We show that the value of the chain propagation constant calculated from nonsteady-state kinetic data is independent of the method of calculation and is determined completely by the instrumental experimental error and the accuracy in determining the initiation rate.