Hydrogen atom abstraction from radical attack

Reaction 6 is the hydrogen atom abstraction from PVA, an important propagation reaction. Since it was shown by the spin-trapping technique using 2-methyl-2-nitrosopropane that only the tertiary hydrogen of polypropylene was abstracted by the alkoxy radical (28), it was assumed that the first attack was also exclusively on the tertiary hydrogen of PVA. The a-hydroxyperoxy radical formed by the addition of oxygen (Reaction... 

Many side reactions compete efficiently with the HAS process. Under non-oxidizing conditions, the cyclohexadienyl radical 1 is rather long lived and can dimerize to 5 (radical-radical coupling) or disproportionate to cyclohexadiene 6 (H-atom abstraction) and substitution product 3 (Scheme 9.2). Long-lived radical 1 may also couple with radicals derived from the radical initiator [8]. These reactions can be considered as termination steps [9]. In addition, radical R can be reduced by hydrogen atom abstraction from the solvent to yield R-H, before the attack on the benzene core preventing the HAS reaction. 

Selective chlorination of the 3-position of thietane 1,1-dioxide may be a consequence of hydrogen atom abstraction by a chlorine atom. Such reactions of chlorine atoms are believed to be influenced by polar effects, preferential hydrogen abstraction occurring remotely from an electron withdrawing group. The free radical chain reaction may be propagated by attack of the 3-thietanyl 1,1-dioxide radical on molecular chlorine. 

Some radicals (e.g., tert-butyl, benzyl, and cyclopropyl), are nucleophilic (they tend to abstract electron-poor hydrogen atoms). The phenyl radical appears to have a very small degree of nucleophilic character. " For longer chains, the field effect continues, and the P position is also deactivated to attack by halogen, though much less so than the a position. We have already mentioned (p. 896) that abstraction of an a hydrogen atom from ring-substituted toluenes can be correlated by the Hammett equation. 

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