Hydrogen abstraction s. Oxidation

Methyl and methylene groups, active, Nucleophiles Hydrogen abstraction s. Oxidation... 

High-valent oxo-complexes, isolated or in situ-generated, interact most often with electron-rich n -systems 1 or suitable C-H bonds with low bond dissociation energy (BDE) in substrates 3 (Fig. 2). These reactions may occur concerted via transition states 1A or 3A leading to epoxides 2 or alcohols 4. On the other hand, a number of epoxidation reactions, such as the Jacobsen-Katsuki epoxidation, is known to proceed by a stepwise pathway via transition state IB to radical intermediate 1C [39]. Similarly, hydrocarbon oxidation to 4 can proceed by a hydrogen abstraction/S ... 

C-Hydrogen, — s. a. Methyl and methylene groups, active, Nucleophiles —, ar active 21, 652 Hydrogen abstraction (s. a. Oxidation)... 

Oxidation (s. a. Autoxidation, Decarboxylation, oxidative. Hydrogen abstraction, Isomerization, oxidative,... 

Ca.ta.lysis, The mechanism of hydrogen abstraction from alcohols to form aldehydes (qv) over silver has been elucidated (11). Silver is the principal catalyst for the production of formaldehyde (qv), the U.S. production of which was 4 x 10 metric tons in 1993. The catalytic oxidation of... 

Hydroperoxide groups react with NO to give only nitrates as the dominant products, with only traces (< 5%) of nitrite in both oxidized polyolefins and in concentrated solutions of model hydroperoxides (-OOH levels from iodometry -ONO and -ON02 levels by IR). As reported by Shelton and Kopczewski we have confirmed that both nitrate and nitrite result from NO reaction with dilute hydroperoxide solutions (24). Rather than the NO-induced 0-0 scission proposed by these authors, our evidence points to hydrogen abstraction by NO (reaction 4). (A similar scheme may explain nitrite formation from alcohols.) Both e.s.r. and FTIR evidence is... 

The photochemistry of thiochromanone 1-oxides has been examined (76CJC455) the principal pathways are /3-hydrogen abstraction with readdition of the sulfinic acid to the alkene (equation 39), and rearrangement to cyclic sulfinates followed by homolysis of the S—O bond. 

For this reaction, the relative rates for different R s are often assumed to be directly related to the bond strengths of the R—H bonds. Many workers (20, 217, 220, 229) have postulated that, during oxidation, hydrogen abstraction from hydrocarbon molecules by radicals should occur at rates determined by the numbers and strengths of C—H bonds present. According to Rice (178), the relative rates at 300° C. should be primary secondary-.tertiary = 1 3 33. 

The oxidation rates for bromoform were slower than the oxidation rates of unsaturated chlorinated aliphatic compounds, including the TCE. Because the hydroxylation rate constant of TCE is 109 Mr1 s 1 and the hydrogen abstraction of bromoform is 1.1 x 108 M 1 s aromatics and alkenes react more rapidly by hydroxyl addition to double bonds than does the more kinetically difficult hydrogen atom abstraction. No oxidative destruction of chloroform by Fenton s reagent was experimentally observed an explanation for this is that both H202 and Fe2+ have rate constants about one magnitude higher with respect to hydroxyl radicals than chloroform. 

Deeble DJ, Schuchmann MN, Steenken S, von Sonntag C (1990) Direct evidence for the formation of thymine radical cations from the reaction of SO/" with thymine derivatives a pulse radiolysis study with optical and conductance detection. J Phys Chem 94 8186-8192 DeFelippis MR, Murthy CP, Faraggi M, Klapper MH (1989) Pulse radiolytic measurement of redox potentials the tyrosine and tryptophan radicals. Biochemistry 28 4847-4853 Delatour T, Douki T, D Ham C, Cadet J (1998) Photosensitization of thymine nucleobase by benzo-phenone through energy transfer, hydrogen abstraction and one-electron oxidation. J Photo-chem Photobiol 44 191-198... 

It is considered in a first approach that both P° and P ° radicals are equally reactive in terminations or oxidations, so that this reaction - as hydrogen abstraction - does not modify the whole kinetics. The oxygen addition to radicals is very fast, k2 10s 109 lmoH1 s-1, so that there is practically no competitive process when 02 is in sufficient concentration to scavenge all the P° radicals. 

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