Kinetic studies radical reactions

Radical clock competition kinetic studies of reactions of Bu3SnH with acyl radicals have been reported. Relative rate constants for reactions of... 

Few kinetic studies of reactions of alkyl radicals with tin hydrides other than Bu3SnH have been reported. Studies of the reactions of the tert-butyl radical with Me3SnH and Ph3SnH were performed by the rotating sector method,80 but an error in absolute values exists in that method as judged by differences in rate constants for reactions of Bu3SnH with alkyl radicals... 

MacLeod, H., Jourdain, L., Poulet, G., and LeBras, G. Kinetic study of reactions of some organic sulfur compounds with OH radicals, Atmos. Environ., 18(12) 2621-2626, 1984. 

The UV absorption spectra of radical cations such as 87 have received attention, and the ESR spectra have been studied and in some cases interpreted. Rate constants for the one-electron reduction of diquat and the salts 82 (n = 3) and 82 (n = 4) have been determined by pulse radiolysis, and kinetic studies involving reactions of the diquat radical cation at hydrogen-evolving metal electrodes have been... 

The kinetics of radical reactions can be studied by direct methods (discussed in Chapter 18 of this volume) or by indirect methods. Indirect kinetic studies require no special instrumentation, and are popular for obtaining relative or absolute rate constants for an intermediate that might be formed in a specific conversion. The radical of interest is generated in a reaction where two pathways compete, the reaction of interest and the basis reaction, for which a rate constant is known. Relative rate constants are then determined from the product mixture by spectroscopy or chromatography and used with the basis rate constant to calculate the absolute rate constant for the reaction of interest. The method is most easily applied... 

Davis, D.D., Machado, G., Conaway, B., Oh, Y., Watson, R. (1976) A temperature dependent kinetic study of reaction of hydroxyl radicals with chloromethane, dichloromethane, trichloromethane and bromomethane. J. Chem. Phys. 65, 1268-1274. 

The flash technique was designed primarily for the study of the kinetics of radical reactions but much information is also obtained from the interpretation of the spectra themselves, and two such spectra, of the radicals CIO and SH, will now be considered. 

Reactions between B and X may conveniently be studied also under conditions where Cx/Ca < 1. In that case the reagent X is consumed during the early parts of the voltammetric wave giving rise to a prepeak (at Ep pre) in front of the main peak (at Ep.main) for the reduction of A, now in a solution that close to the electrode is essentially free from X [119]. An example of such a voltammogram is shown in Fig. 17(a). The rate constant may be obtained from the potential difference Ep pre — Ep main, which has been tabulated for a number of reaction mechanisms [119]. This method has been used extensively in kinetic studies of reactions between radical cations and nucleophiles [119-122]. 

Within the last two decades Electron Spin Resonance-(ESR) spectroscopy has become a standard experimental technique in electrochemical research. The main interest was in the field of electrochemical generation of radicals to characterize their structure by ESR spectroscopy or to prove their presence in electrode reactions. The studies have been extended to the kinetics of radical reactions and the set up of reaction mechanism, to the solvation phenomena in radical electron densities and to radical conformation and ion complex structure. The latest development is the study of the electrode materials and their surface layers in electrochemical systems by simultaneous ESR spectroscopic and electrochemical measurements, e.g., of polymer modified electrodes. 

Kinetic Studies of Reactions of Alkylperoxy and Haloalkylperoxy Radicals with NO. 

Kinetic Studies of Reactions of Alkylperoxy and Haloalkylperoxy Radicals with NO. A Structure-Activity Relationship for Reactions... 

Theoretical and experimental studies are needed to specify the kinetics of radical reactions involving H2O molecules. These reactions, involving high activation energy, are insignificant at ambient and elevated temperatures, but can contribute significantly to the chemistry in near and supercritical water. 

Since the kinetics studies the reaction as a process, it has the specific methodology the body of theoretical concepts and experimental methods, which allow the study and analysis of the chemical reaction as an evolution process that develops in time. The experimental kinetics possesses various methods to perform the reaction and control it in time. The kinetic methods for studying fast reactions (stop-flow, pulse, etc.) have been developed during recent 40 years along with procedures and methods for the generation and study of active intermediate compounds free atoms and radicals, labile ions and complexes. The methods for perturbation of the chemical reaction during its course were invented. Mathematical simulation and modem computer techinique are widely used for the theoretical description of the reaction as a process. 

In contrast to the ionization of C q after vibrational excitation, typical multiphoton ionization proceeds via the excitation of higher electronic levels. In principle, multiphoton ionization can either be used to generate ions and to study their reactions, or as a sensitive detection technique for atoms, molecules, and radicals in reaction kinetics. The second application is more common. In most cases of excitation with visible or UV laser radiation, a few photons are enough to reach or exceed the ionization limit. A particularly important teclmique is resonantly enlianced multiphoton ionization (REMPI), which exploits the resonance of monocluomatic laser radiation with one or several intennediate levels (in one-photon or in multiphoton processes). The mechanisms are distinguished according to the number of photons leading to the resonant intennediate levels and to tire final level, as illustrated in figure B2.5.16. Several lasers of different frequencies may be combined. 

Structure-reactivity relationships can be probed by measurements of rates and equiUbria, as was diseussed in Chapter 4. Direct comparison of reaction rates is used relatively less often in the study of radical reactions than for heterolytic reactions. Instead, competition methods have frequently been used. The basis of competition methods lies in the rate expression for a reaction, and the results can be just as valid a comparison of relative reactivity as directly measured rates, provided the two competing processes are of the same kinetic order. Suppose that it is desired to compare the reactivity of two related compounds, B—X and B—Y, in a hypothetical sequence ... 

A study on the kinetics of the reactions of phenylseleno radicals with vinyl monomers has also been reported.464... 

Dithiols and dienes may react spontaneously to afford dithiols or dienes depending on the monomer dithiol ratio.221 However, the precise mechanism of radical formation is not known. More commonly, pholoinilialion or conventional radical initiators are employed. The initiation process requires formation of a radical to abstract from thiol or add to the diene then propagation can occur according to the steps shown in Scheme 7.17 until termination occurs by radical-radical reaction. Termination is usually written as involving the monomer-derived radicals. The process is remarkably tolerant of oxygen and impurities. The kinetics of the tbiol-ene photopolymerizalion have been studied by Bowman and... 

Kinetic studies of the oxidation of sulphoxides to sulphones by chromium(VI) species have been carried out131-133. The reaction has been found to be first order with respect to the chromium(VI) species and the sulphoxide and second order with respect to acid. At high sulphoxide concentrations the order with respect to sulphoxide is two. The proposed mechanism involves an electron transfer from the sulphoxide to the active chromium(VI) species (HCr03+ in strong acidic media) in the rate-determining step producing a sulphoxide radical cation which further reacts to give the sulphone. 

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