SRN1 reactions termination steps

At this point, it can be concluded that the direct and indirect electrochemical approach of the reaction in the case of aryl halides has provided a quantitative kinetic demonstration of the SRN1 mechanism and the establishment of the nature of the side-reactions (termination steps in the chain process). In poor H-atom donor solvents, the latter involve electron-transfer reduction of the aryl radical. 

The experiments in liquid ammonia described above and the corresponding theoretical analyses have allowed a quantitative confirmation of the SRN1 mechanism and the discovery of the nature of the side-reactions, i.e. the termination steps in the chain process. As discussed in Section 2, pp. 40-45, another means of destroying aryl radicals in organic solvents, besides... 

The previous material has illustrated the ability of spin traps to act as one-electron oxidizers. This property is even more pronounced in the interactions of traps with anion radicals. Traps can block the ion radical pathway. In other words, they inhibit the whole reaction, including the ion radical step. This may be explained by both oxidation of the substrate anion radical and chain termination due to oxidation of the product anion radical. An illustrative example is the inhibition of SRN1 nucleophilic substitution of 2-chloroquinoxaline by the radical trap bis(te/f-butyl)nitrone (Carver, Hubband, Wolfe, 1982). 

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