Racemization in SnI reactions


Effect of solvent blend on the rate of magnesium oxide-phenolic resin reaction  [c.663]

The lack of suitable catalysts is the most common reason preventing the exploitation of novel reaction paths. At the first stage of design, it is impossible to look ahead and see all the consequences of choosing one reaction path or another, but some things are clear even at this stage. Consider the following example.  [c.16]

As well as depending on catalyst porosity, the reaction rate is some function of the reactant concentrations, temperature, and pressure. However, this function may not be as simple as in the case of uncatalyzed reactions. Before a reaction can take place, the reactants must diffuse through the pores to the solid surface. This results in a situation where either reaction or diffusion can be the rate-limiting process. Alternatively, it may be that reaction speed and diffusion have an almost equal effect. If reaction is rate limiting, as tends to occur in a lower temperature range, the effects of concentration and temperature are those typical of chemical reaction. On the other hand, if diffusion is rate limiting, as tends to occur in a higher temperature range, the effects of concentration and temperature are those characteristic of diffusion. In the transitional region, where both reaction and diffusion affect the overall rate, the effects of temperature and concentration are often rather complex.  [c.47]

In Fig. 8.3, the only cost forcing the optimal conversion hack from high values is that of the reactor. Hence, for such simple reaction systems, a high optimal conversion would he expected. This was the reason in Chap. 2 that an initial value of reactor conversion of 0.95 was chosen for simple reaction systems.  [c.243]

One reason the polyad-breaking couplings are of interest is because they govern the long-time intramolecular energy flow, which is important for theories on reaction dynamics. These are considered elsewhere in this Encyclopedia and in monographs [6] and will not be considered fiirther here. The long-time energy flow may  [c.74]

Let us consider the general properties of a potential energy surface for a bimolecular reaction involving tln-ee atoms, i.e. equation (A3.7.1) with A, B and C all atomic species. A tln-ee-atom reaction requires a tln-ee-dimensional ftmction. It is more convenient to plot two-dimensional surfaces in which all coordinates but two are allowed to vary. Figure A3.7.1 shows a typical example of a potential energy surface contour plot for a collinear tln-ee-atom reaction. The dotted curve represents the minimum energy path, or reaction coordinate, that leads from reactants on the lower right to products on the upper left. The reactant and product valleys (often referred to as the entrance and exit valleys, respectively) are connected by the transition-state region, where the transfomiation from reactants to products occurs, and ends in the product valley at the upper left. The potential energy surface shown in Figure A3.7.1 is characteristic of a direct reaction, in that there is a single barrier (marked by J m Figure A3.7.1 ) along the minimum energy path in the transition-state region. In the other general class of bimolecular reaction, a complex reaction, one finds a well rather than a barrier in the transition-state region.  [c.870]

At this point it is reasonable to ask whether comparing classical or quantum mechanical scattering calculations on model surfaces to asymptotic experimental observables such as the product energy and angular distributions is the best way to find the true potential energy surface for the F + FI2 (or any other) reaction. From an experimental perspective, it would be desirable to probe the transition-state region of the F + FI2 reaction in order to obtain a more direct characterization of the bending potential, since this appears to be the key feature of the surface. From a theoretical perspective, it would seem that, with the vastly increased computational power at one s disposal compared to 10 years ago, it should be possible to construct a chemically accurate potential energy surface based entirely on ab initio calculations, with no reliance upon empirical corrections. Quite recently, both developments have come to pass and have been applied to the F + FI2 reaction.  [c.878]

Keck J 1960 Variational theory of chemical reaction rates applied to three-body recombinations J. Chem. Phys. 32 1035 Anderson J B 1973 Statistical theories of chemical reactions. Distributions in the transition region J. Chem. Phys. 58 4684  [c.896]

For vibrational effects in the dynamics, the location of the dissociation barrier within the curved interaction region of figure A3.9.8 is crucial. If the barrier occurs largely before the curved region, it is an early barrier at point E, then vibration will not promote reaction as it occurs largely at right angles to the barrier. In contrast, if the barrier occurs when the bond is already extended, say at L (a late barrier) in the figure, the vibration is now clearly helping the molecule to attack this barrier, and can substantially enliance reaction.  [c.908]

Figure A3.12.10. Schematic diagram of the one-dimensional reaction coordinate and the energy levels perpendicular to it in the region of the transition state. As the molecule s energy is increased, the number of states perpendicular to the reaction coordinate increases, thereby increasing the rate of reaction. (Adapted from [4].) Figure A3.12.10. Schematic diagram of the one-dimensional reaction coordinate and the energy levels perpendicular to it in the region of the transition state. As the molecule s energy is increased, the number of states perpendicular to the reaction coordinate increases, thereby increasing the rate of reaction. (Adapted from [4].)
Deutsche Texaco developed a tridde-bed process to avoid the disadvantages of the gas-phase process. In the tridde-bed process, a mixture of Hquid water and propylene gas in a molar ratio of 12 to 15 1 is introduced at the top of a fixed-bed reactor and allowed to tridde down over a sulfonic acid ion-exchange resin. Reaction between the Hquid and gas phases takes place at 130—160°C and 8—10 MPa (80—100 atm), forming aqueous isopropyl alcohol. Propylene conversions per pass are greater than 75%, and isopropyl alcohol selectivity is 93%. Only 92 wt % propylene purity is needed for this process. Approximately 5% diisopropyl ether and some alcohols of the higher oligomers form as by-products. The life of the cation-exchange resin is at least eight months.  [c.109]

Rosenheim reaction CHCI3+ trichloroacetic acid in red color develops and changes to  [c.133]

Rosenheim reaction CHCI3 + lead tetraacetate in green fluorescence not given by esters of provitamin D can  [c.133]

One common reason for imposing constraints results from areas of integrity A process is often normally designed to have logically identifiable sections or areas. An example might be reaction area and separation area of the process. These areas are kept separate for reasons such as start-up, shutdown, operational fiexibility, safety, etc. The areas are often made operationally independent through the use of intermediate storage of process materials between the areas. Such independent areas are generally described as areas of integrity and impose constraints on the ability to transfer heat. Clearly, to maintain operational indepedence, two areas cannot be dependent on each other for heating and cooling by recovery.  [c.181]

CjHiO. Colourless liquid with a peculiar odour darkens on exposure to light and air b.p. 162°C. It occurs in many essential oils and in fusel oil. Manufactured by heating corncobs, oal hulls or other pentose-containing material with steam under pressure at 180°C and fractionally distilling the liquor. Undergoes the Cannizzaro reaction with alkalis to give furoic acid and furfuryl alcohol. Reacts with ammonia to give furfuramide. Oxidized by sodium chlorate(V) in the presence of VjOj to give fumaric acid. Forms resins with phenol, aniline and propanone. Used as a solvent for decolourizing rosin and in the solvent extraction of mineral oils.  [c.184]

Chemisorption may be slow and the rate behavior indicative of the presence of an activation energy it may, in fact, be possible for a gas to be physically adsorbed at first, and then, more slowly, to enter into some chemical reaction with the surface of the solid. At low temperatures, chemisorption may be so slow that for practical purposes only physical adsorption is observed, whereas, at high temperatures, physical adsorption is small (because of the low adsorption energy), and only chemisorption occurs. An example is that of hydrogen on nickel, for which a schematic isobar is shown in Fig. XVII-2. Curve 1 shows the normal decrease in physical adsorption with temperature, and curve 2, that for chemisorption. In the transition region, curve 3, the rate of chemisorption is slow, but not negligible, so the location of the points depends on the equilibration time allowed curve 3 is therefore not an equilibrium one and is not retraced on cooling, but rather some curve between 3 and 4 is followed, depending on the rate.  [c.601]

Basic features of solvent effects can be illustrated by considering the variation of the rate constant of a unimolecular reaction as one gradually passes from the low-pressure gas phase into the regime of liquid-like densities [1] (see figure A3.6.1.1 At low pressures, where the rate is controlled by themial activation in isolated binary collisions with bath gas molecules, is proportional to pressure, i.e. it is in the low-pressure limit /cq. Raising the pressure fiirther, one reaches the fall-off region where the pressure dependence of becomes increasingly weaker until, eventually, it attains the constant so-called high-pressure limit k. At this stage, collisions with bath gas molecules, which can still be considered as isolated binary events, are sufficiently frequent to sustain an equilibrium distribution over rotational and vibrational degrees of freedom of the reactant molecule, and is detemiined entirely by the intramolecular motion along the reaction patli. k may be calculated by statistical theories (see chapter A3.4) if the potential-energy (liyper)surface (PES) for the reaction is known. What kind of additional effects can be expected, if the density of the compressed bath gas approaches that of a dense fluid Ideally, there will be little fiirther change, as equilibration becomes even more effective because of pemianent energy exchange with the dense heat bath. So, even with more confidence than in the gas phase, one could predict the rate constant using statistical reaction rate theories such as, for example, transition state theory (TST). However, this ideal picture may break down if (i) there is an appreciable change in charge distribution or molar volume as the system moves along the reaction path from reactant to product state, (ii) the reaction entails large-amplitude structural changes that are subject to solvent frictional forces retarding the motion along the reaction path or (iii) motion along the reaction path is sufficiently fast that tliemial equilibrium over all degrees of freedom of the solute and the bath cannot be maintained.  [c.830]

As a multidimensional PES for the reaction from quantum chemical calculations is not available at present, one does not know the reason for the surprismg barrier effect in excited tran.s-stilbene. One could suspect diat tran.s-stilbene possesses already a significant amount of zwitterionic character in the confomiation at the barrier top, implying a fairly Tate barrier along the reaction path towards the twisted perpendicular structure. On the other hand, it could also be possible that die effective barrier changes with viscosity as a result of a multidimensional barrier crossing process along a curved reaction path.  [c.857]

The experimental values of K(r ) have a maximum at a viscosity close to 3 cP and varies by about 15% over the entire viscosity range studied. As discussed above, this unexpected dependence of k on solvent friction m liquid CS2 is thought to be caused by a relatively weak intramolecular coupling of the reaction coordmate to the remaining modes in cyclohexane. At viscosities below the maximum, motion along the reaction coordinate due to the reduction of the accessible phase space region is fast. The barrier passage is still in the inertial regime, and the strong coupling to the solvent leads to increasingly rapid stabilization in the product well. With increasing solvent friction, the barrier crossing enters the difhisive regime and begins to show a slowdown with further increasing solvent viscosity.  [c.859]

This definition holds for multiple dimensions as well for A particles, the classical transition state is a saddle point that is unbound along the reaction coordinate but bound along the 3N- 7 remaining coordinates. A cut tlirough the surface at the transition state perpendicular to the reaction coordinate represents a 3A - 7 dimensional dividing surface that acts as a bottleneck between reactants and products. The nature of the transition state and, more generally, the region of the potential energy in the vicinity of the transition state (referred to above as the transition-state region) therefore plays a major role in detennining many of the experimental observables of a reaction such as the rate constant and the product energy and angrilar distributions. For this reason, the transition-state region is the most important part of the potential energy surface from a computational (and experunental) perspective.  [c.871]

An incredible variety of experimental teclmiques have been developed over the years to address these issues. One of the most general is the crossed molecular beams method with mass spectrometric detection of the products, an experiment developed by Lee, Flerschbach and co-workers [18,19]. A schematic illustration of one version of the experiment is shown in figure A3.7.2. Two collimated beams of reactants cross in a vacuum chamber under single-collision conditions. The scattered products are detected by a rotatable mass spectrometer, in which the products are ionized by electron impact and mass selected by a quadnipole mass spectrometer. By measuring mass spectra as a frinction of scattering angle, one obtains angular distributions for all reaction products. In addition, by chopping either the products or one of the reactant beams with a rapidly spiiming slotted wheel one can detenuine the time of flight of each product from the interaction region, where the two beams cross, to the ionizer, and from this the product translational energy can be detenuined at each scattering angle. The resulting product translational energy distributions P Ej) also contain infonuation on the internal energy distribution of the products via conservation of energy, so long as the reactant collision energy is well defined.  [c.872]

The probability matrix plays an important role in many processes in chemical physics. For chemical reactions, the probability of reaction is often limited by tunnelling tlnough a barrier, or by the fonnation of metastable states (resonances) in an intennediate well. Equivalently, the conductivity of a molecular wire is related to the probability of transmission of conduction electrons tlttough the junction region between the wire and the electrodes to which the wire is attached.  [c.964]

A general reaction scheme for CIDNP is shown in llgnre B1.16.4B. where the radical dynamics in each region  [c.1595]

Ion beam analysis grew out of nuclear physics research on cross sections and reaction products involved in atomic collisions. In this work million volt accelerators were developed and used extensively. As the energies of the incident particles increased, the lower energy accelerators became available for use in solid state applications. The early nuclear physics research used magnetic spectrometers to measure the energies of the particles. This analytical procedure was time consuming and the advent of the semiconductor nuclear particle detector allowed simultaneous detection of all particle energies. It was an energy dispersive spectrometer. The semiconductor detector is a Schottky barrier (typically a gold film on silicon) or shallow diflfiised p-n junction with the active region defined by the high electric field in the depletion layer. The active region extends tens of microns below the surface of the detector so that in almost every application the penetration of the energetic particles is confined within the active region. The response of the detector is linear with the energy of the particles providmg a true particle energy spectrometer.  [c.1828]

The technology of focusing ions is still at the stage where the resolution of the NMP does not compete with the electron microprobe. A set of deflection plates allows movement or scaiming of the ion beam and, using computer control, the position of the bombarding beam is known. At each point of irradiation, analytical data are acquired. In this way, the analytical infomiation obtained can be presented as an image. NaPirally, the imaging capabilities of the NMP is limited by the sensitivity of each teclmique used shice an entire spectrum must be collected at each pixel in the image. For example, a 128 x 128 pixel image is equivalent to 16 384 single-point analyses. For this reason the analytical techniques used in imaging are mostly limited to PIXE hi the case of trace elements, RBS and forward recoil spectrometry (FRS) for depth infomiation and light elements and nuclear reaction analysis (NRA) to the detection of elements at high concentrations. Naturally the NMP can also be used in a point analysis mode, as for example in the case of geological applications [28]. Here the gram sizes that need to be analysed are often of the order of a few microns and a reasonably small bombarding beam is necessary to limit the analysis to a specific gram.  [c.1844]

In a potential-step experiment, the potential of the working electrode is instantaneously stepped from a value where no reaction occurs to a value where the electrode reaction under investigation takes place and the current versus time (cluonoamperometry) or the charge versus time (cluonocoulometry) response is recorded. The transient obtained depends upon the potential applied and whether it is stepped into a diffrision control, in an electron transfer control or in a mixed control region. Under diffusion control the transient may be described by the Cottrell equation obtained by solving Pick s second law witii the appropriate initial and boundary conditions [1, 2, 3, 4, 5 and 6]  [c.1929]

This teclnhque can be used both to pennit the spectroscopic detection of molecules, such as H2 and HCl, whose first electronic transition lies in the vacuum ultraviolet spectral region, for which laser excitation is possible but inconvenient [ ], or molecules such as CH that do not fluoresce. With 2-photon excitation, the required wavelengdis are in the ultraviolet, conveniently generated by frequency-doubled dye lasers, rather than 1-photon excitation in the vacuum ultraviolet. Figure B2.3.17 displays 2 + 1 REMPI spectra of the HCl and DCl products, both in their v = 0 vibrational levels, from the Cl + (CHg) CD reaction [ ]. For some electronic states of HCl/DCl, both parent and fragment ions are produced, and the spectrum in figure B2.3.17 for the DCl product was recorded by monitoring mass 2 (D ions. In this case, both isotopomers (D Cl and D Cl) are detected.  [c.2083]


See pages that mention the term Racemization in SnI reactions : [c.475]    [c.663]    [c.310]    [c.385]    [c.155]    [c.695]    [c.246]    [c.874]    [c.875]    [c.889]    [c.892]    [c.909]    [c.1008]    [c.1025]    [c.1047]    [c.1069]    [c.1103]    [c.1115]    [c.1591]    [c.1596]    [c.1835]    [c.1904]    [c.1933]    [c.1968]   
Carey organic chemistry (0) -- [ c.342 , c.343 ]

Organic chemistry (0) -- [ c.342 , c.343 ]