Trapping of radicals

The peroxide-catalysed addition of dimethyl phosphonate to norborna-diene gives nortricyclenes as well as norbornenes. Usually, radicals react with this diene to give only nortricyclene derivatives. The ease of hydrogen abstraction from the parent phosphonate undoubtedly favours trapping of radical (8). 

Nucleophilic Trapping of Radical Cations. To investigate some of the properties of Mh radical cations these intermediates have been generated in two one-electron oxidant systems. The first contains iodine as oxidant and pyridine as nucleophile and solvent (8-10), while the second contains Mn(0Ac) in acetic acid (10,11). Studies with a number of PAH indicate that the formation of pyridinium-PAH or acetoxy-PAH by one-electron oxidation with Mn(0Ac)3 or iodine, respectively, is related to the ionization potential (IP) of the PAH. For PAH with relatively high IP, such as phenanthrene, chrysene, 5-methyl chrysene and dibenz[a,h]anthracene, no reaction occurs with these two oxidant systems. Another important factor influencing the specific reactivity of PAH radical cations with nucleophiles is localization of the positive charge at one or a few carbon atoms in the radical cation. 

The few cases in which thermodynamic control is not effective appear to be dominated by steric effects39. Thus, trapping of radical 25 with triphenyltin hydride regioselec-tively yields product 26, in which the double bond is separated from the ester through a methylene bridge (equation 12). 

TRAPPING OF RADICALS GENERATED IN THE SOLID STATE OR IN THE GAS PHASE... 

Spin trapping of radicals generated by ultrasound (sonolysis) 126... 

Nucleic Acids. - Recent EPR studies of radical attack and formation upon DNA are reported elsewhere in this volume, by Sevilla and Becker, and therefore will not be described here in any detail. Findings of particular biomedical relevance include the spin trapping of radicals resulting from the decomposition of chloramines formed in the reaction of HOC1 with polynucleosides, RNA and... 

Trapping of radicals formed through the thermal degradation and combustion process... 

Dithiolane (1) itself is unstable, and easily polymerizes (54JA4348), but photolysis of lipoic add (29) in the presence of aldehydes gives a product (70) by trapping of radicals (76CC92). 

Other selenoacetals have been prepared by means of radical phenylseleno group transfer reactions and by trapping of radicals with diphenyl diselenide, these procedures will be discussed later in this chapter (Sects. 3.1 and 5.2). 

The development of regiospecific trapping of radicals arising by cyclization should prove useful in synthesis. Irradiation of the bromoalkane (196) in the... 

Rabinkov, A., Miron, T., Konnstantinovski, L., Wilchek, M., Mirelman, D. and Weiner, L. (1998) The mode of action of allicin Trapping of radicals and interaction with thiol containing proteins. Biochem. Biophys. Acta. 1379(2) 233-244. 

These methods are related to the better known trapping of radicals, trapping of carbanions elaborated by Szwarc ( ) and, more recently, end-capping with phenolates in cationic polymerization (9,10,11). 

Generation and trapping of radical cations of a,co-diphenylpolyenes within the channels of pentasil zeolites provides an environment which allows these transient species to be spectroscopically characterized . Similarly, complexation of xanthone in cyclodextrin has made it possible for the triplet state of this molecule to be fully characterized . Association and dissociation processes are related to the dipoles developed in the complex and in solution. A unimodal Lorentzian lifetime distribution for 2-anilinonaphthalene-6-sulphonate B-cyclodextran inclusion complexes have been recovered by multifrequency phase-modulation fluorometry in the presence of the quenchers Cu, acrylamide, and I . Both the fluorescence and phosphorescence spectra of benzo[f]quinoline adsorbed on p-cyclodextrin/NaCl have been determined as a function of temperature . 

The decay of H-atoms on PVG (51) also showed a similar cascade decay but followed second order kinetics. Similar cascade decay of radicals have been reported to occur in polymers which have been Y-irradlated (54) and is attributed to the trapping of radicals in preferential sites within the solid. 

Scheme 28. Proposed mechanism for MAO processing of t-amino-l-benzoylcyclobutane and trapping of radical intermediates by a-phenyl-A-/m-butylnitrone (PBN) (J20).

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