Radical trapping reaction

It has subsequently been shown (Maeda et ai, 1978) that the rates of these alkyl-radical trapping reactions show no significant solvent dependence. 

The complexes react with oxygen to form metal oxides (eq. 18). This reaction is likely a radical trapping reaction but may involve excited state electron transfer. 

In one study,52 the temperature dependence of quantum yields was investigated using polymer 5 (prepared by the route in equation 26). Thin films of polymer 5 are photochemically reactive ( = 532 or 546 nm) in the absence of oxygen, giving the products shown in Scheme 7.19 The reaction is thus similar to the photochemical radical trapping reactions of the Cp2Mo2(CO)6 dimer that take place in solution in the presence of an alkyl halide, and an analogous mechanism was proposed (Scheme 7). 

SCHEME 8. Reaction of a photoreactive species to form a caged radical pair followed by a radical trapping reaction. 

Two groups of anti-oxidants are of practical importance hindered phenol light stabilisers (HPLS) and hindered amine light stabilisers (HALS). Examples are shown in Fig. 13.7 and the mechanism of the radical trapping reaction is shown in Fig. 13.8. They are often combined with UV absorbents (for partly synergistic effects) and mostly used for the fibre protection. 

The almost negligible net retention observed in the reactions of the chloride 52-CI with LiN, NaN and KN excludes even the involvement of a cyclopropyl radical trapping reaction as being responsible for the distinct net retentions observed in the reductions of the bromide and the iodide 51-Br and 5(1-1, respectively. 

The availability of radical clocks for -hybridized carbon systems has been limited by the high reactivity of phenyl and vinyl radicals and by the lack of appropriate methods for preparation of these radicals for direct kinetic studies. Competition kinetic studies have given relative rate constants for some radical clocks in this group, but absolute rate constants for the radical-trapping reactions used in the competitions are not generally available. In that regard, one should note that reported rate constants for reactions of BuySnH with the phenyl and 2,2-dimethylvinyl radicals [29] were later vitiated when it was found that these radicals had not been produced cleanly. 

The free radical trapping reaction (kxf) of Scheme 3 involves a collisionally formed cage pair (where the trapping agent (T) and the alkyl (R ) radical are the chemically reactive components) which is formally identical to that for free radical self-termination discussed above. Scheme 4 provides this... 

TGM-3 proceeds for 8 h when the temperature is increased to 90°C the radical trapping reaction is practically finished in 1 h [16]. 

Pig. 5. Carbon-centered free-radical trapping reactions with benzofuranones. 

Photochemical Reactions in Solution. Metal-metal bonds react photochemically in solution according to one of three fundamental types of reactions (4). (1) They react with radical traps to form monomeric complexes (e.g., equation 10) (2) they react with ligands to form ionic disproportionation products (e.g., equation 11) and (3) they react with oxygen to form metal oxides (equation 12). (lie latter reaction is likely a radical trapping reaction in the sense that an oxygen molecule reacts with a photogenerated metal radical.)... 

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