How do radicals react

How do free radicals interact with a polymer to cause degradation Why are many heat stabilizers chemicals that react to quench the free radicals ... 

Vitamin E and BHT are radical inhibitors, so they terminate radical chain mechanisms by reacting with radicals. How do they trap radicals Both vitamin E and BHT use a hydroxy group bonded to a benzene ring—a general structure called a phenol. 

Yet how do we know, in this case, that every isobutyl radical that is formed ultimately yields a molecule of isobutyl chloride Suppose some isobutyl radicals were to change- by rearrangement of atoms—into /erZ-butyl radicals, which then react with chlorine to yield /cr/-butyl chloride. This supposition is not so far-... 

Quinones are firmly established in photosynthesis models. But how about vitamins E and K How do quinones work in animals First of all they transport electrons in a similar way as in photosynthesis (Metzler, 1977 Voet, 1990). Second, tocopherol is known to act as an antioxidant or radical quencher. The radical chain starting with the decomposition of unsaturated lipid peroxides, for example, is inhibited by tocopherol, which produces long-lived semiquinone radicals (Scheme 7.2.10). Vitamin E prevents, for example, sterility in rats fed rancid lipids. Vitamin E in connection with carotenes is also used as a stabilizer for diet margarines containing large amounts of essential fatty acids. Another possible activity of tocopherol is participation in oxidative phosphorylation a hydroquinone is mono-esterified with phosphoric acid to form a quinol phosphate and then oxidized to the quinone. The cationic quinone-phosphate adduct then reacts with anionic phosphate to form pyrophosphate (Scheme 7.2.10), (Wang, 1969 Breslow, 1980 Isler and Brubacher, 1982). 

How does this order of the rates v > vtom come about As high-energy species, radical intermediates react exergonically with most reaction partners. According to the Hammond postulate, they do this very rapidly. Radicals actually often react with the first reaction partner they encounter. Their average lifetime is therefore very short. The probability of a termination step in which two such short-lived radicals meet is consequently low. 

In Chapter 17 we introduced nuclrophilic substitution at saturated carbon, using as an example some alkyl bromides. Now, radicals do react with alkyl halides—but not at carbon You ve seen how alkyl halides undergo substitution at bromine with tin radicals. The difference in reactivity between, say, organolithiums and radicals, both of them highly reactive, is nicely illustrated by the way in which they react with enones. 

We can produce hydrogen peroxide and hydroxyl radicals, but do we really Our bodies have evolved efficient mechanisms for eliminating both superoxide radicals and hydrogen peroxide before they can react with iron to produce hydroxyl radicals (we will look at these mechanisms in more detail in Chapter 10). Is there any way of working out how many hydroxyl radicals are actually formed in the body despite these mechanisms ... 

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