Showing papers on "Elementary reaction published in 1968"

Stereoselection in the Elementary steps of Organic Reactions

Abstract: Publisher Summary This chapter describes a number of principles or causes of stereoselection associated with bonding, steric, thermodynamic, electrical, and mechanical factors, inherent in the stereoprocess It deals with the relation between the properties of intermediates, such as carbanion or syn-anti isomers, rate and equilibrium conditions and stereoselectivity are also discussed The chapter also examines representative systems and reactions to see the relevance of the principles of stereoselection The focus is on the stereo-process that include two axioms—every reaction at the molecular level is stereospecific (axiom 1) and for a collection of molecules the elementary reaction is stereoselective (axiom 2) The shape of simple species is examined Both valence bond (VB) and molecular orbital (MO) theories are used to explain the observed shapes of molecules The preferred shapes of the simple species are known or can be guessed from the numbers and kinds of bonding and nonbonding electron pairs Several valence bond results and molecular orbital results are discussed

The reaction of O(23P) atoms with 1,1-difluoro-olefins

Abstract: The occurrence of the elementary reaction O(23P)+ C2F4→ CF2O + CF2 has been verified through flash photolysis of NO2–C2F4 mixtures. A new class of reaction of the type O(23P)+ CF2= CXY [graphic omitted] has been discovered; when X, Y = halogen, the biradical intermediate leading to step (b) is formed preferentially. The transient production of the halogenocarbene CXY has been inferred from the results of photolysis in the presence of oxygen.

The kinetics of elementary reactions involving the oxides of sulphur IV. The formation of electronically excited sulphur dioxide on surfaces

Abstract: Chemiluminescence from the reaction between O and SO has been studied in a flow system down to 10 $\mu$mHg pressure. The formation of electronically excited SO$\_2$ in the $^1$B$\_1$ and $^3$B$\_1$ states is shown to be due to a reaction between SO and chemisorbed oxygen atoms, for which a heat of adsorption of 25-30 kcal/mole is deduced. Analysis of the spatial distribution of the visible emission yields a radiative life of (7.5 $\pm$ 2.0) x 10$^{-4}$ s for the $^3$B$\_1$ state of SO$_2$.

The Kinetics of Substitution Reactions Involving Metal Complexes. XII. The Reactions between Copper(II) Ions and Zinc(II)-nitrilotriacetate Complexes

Abstract: The kinetic study of the substitution reaction of copper(II) ions and zinc(II)-nitrilotriacetate complexes in acetate buffer solutions has been carried out with the same procedure as reported previously. The reaction was treated as to proceed through both hydrated metal ions and monoacetato complexes. The rate constants for eight elementary reaction paths, of which four involve the hydrated copper(II) ions and the others the monoacetatocopper(II) complexes, were determined at ionic strength 0.23 at 0°C. The values obtained indicate that all the reactions proceeding through hydrated copper(II) ions are faster than the corresponding reactions proceeding through monoacetatocopper(II) complexes.

Computer studies of reaction profiles in gas detonations

Abstract: : A computer program has been written which numerically integrates the chemical reaction rate equations through the conditions behind a steady-state shock wave. This program has been applied to the calculation of profiles of temperature, pressure, density and concentration in unidimensional detonations in stoichiometric hydrogen-oxygen mixtures, using the Zeldovich-Doring-von Neumann model. Initial pressures were in the range 30-760 torr, and the initial temperature was 300K. Twenty-six elementary reactions involving the chemical species H2, O2, H2O, HO2, OH, H, and O were taken into account in the integration. Data on the rates of the chemical reactions were obtained from the literature. Induction periods and reaction times obtained from the profiles were compared with experimental determinations, and it was found that the computed rates appear to be faster than is observed experimentally. Some possible reasons for this difference are discussed. (Author)

Kinetics of the Elementary Reactions.

Abstract: : The photochemical decomposition of gaseous nitrosyl fluoride has been studied at pressures between 5.0 and 20 torr in the presence of ethylene and other hydrocarbons and inert gases. The inital photochemical act results in the formation of one or more electronically excited states of ONF which may decompose, or on collision with another molecule, be deactivated or induced to decompose. (Author)

General formulation and numerical solution of reaction rate problems

Abstract: : A scheme for constructing the rate equations for a general chemical reaction mechanism consisting of any number of elementary equations and chemical species was devised. The elementary reaction equations do not require special coding and can be written in terms of their chemical symbols. The construction of the rate equations and their solution using the fourth order Runge-Kutta method were programmed for the CDC-6400 computer. The equations can be solved for the following conditions: Isothermal constant volume; isothermal constant pressure; specified temperature and pressure variaton; adiabatic constant volume; adiabatic constant pressure; adiabatic with specified pressure variation. The adiabatic cases can be modified by allowing heat transfer. A description of the computer program and sample calculations are presented. (Author)

Calculations of the rate constants of elementary reactions

Abstract: 1. Various types of reactions of radicals with molecules are also determined by different types of transition complexes, the difference of which lies in the number of rotational degrees of freedom (in this case it is assumed that all the vibrational statistical sums are close to one — sufficiently low temperature). 2. The phenomenon of the compensation effect is explained by the fact that reactions proceeding with large activation energies (reactions of stripping) have a transition complex possessing a large number of rotational degrees of freedom; there is free rotation of particles in the complex, which determines the large values of the preexponential factor. Reactions proceeding with lower activation energies have complexes with a smaller number of rotational degrees of freedom — the complex is more “rigid,” which leads to lower values of the preexponential factor and to a compensation effect. 3. The decrease in the preexponential factor of the reaction rate constant with increasing complexity of the molecule (for identical reactions) is evidence that the experimentally measured constant is a summary quantity.

Remarks on the treatment of heterogeneous catalysis

Abstract: Summary The mass action law successfully applied to homogeneous elementary reactions (or steps for short) was shown applicable to heterogeneous steps only in unexpectedly limited cases on account of the quantum-mechanically inferable interaction among adsorbed species. In case of an appreciable interaction, especially when it varies, e. g. with change of concen­ trations in question, the rate of step could only be reasonably dedt:ced from the statistical mechanics of the whole mass of interacting species which IS usually macroscopic and in thermal equilibrium.7,S) The rate equation thus deduced is called the generalized rate equation, which includes the rate equation of the absolute rate theory,I.2) applicable along with the mass action law, as its special case. The generalized rate equation was illustrated and the critical state of a step was located for contrasting the generalized rate equation with the absolute rate theory,l,2) The rates of the Langmuir-Hinshelwood and Rideal mechanisms were derived as functions of concen­ trations of reactants in gas phase by the mass action law, on the one hand, and by the generalized rate equation ignoring the interaction among adsorbates, on the other hand. The functional forms obtained in the respective cases were identical as otherwise generally demonstrated and their comparison revealed the statistical mechanical contents of kinetic constants involved in the former derivation, directing toward the incorporation of interaction. The incorporation of interaction was exemplified systematically as follows with the catalytic mechanism of hydrogen electrode reaction, where the recombination of hydrogen adatoms determined the rate.