Electron Pushing for Benzyne Reactions

Regiochemical possibilities for reactions involving benzyne. The regiochemical preferences can be predicted by an analysis of whether Y is an EWG or EDG. A. Ortho reactants, B. Para reactants, and C. Meta reactants. 

Besides nucleophilic and electrophilic pathways for aromatic substitutions, there are also radical pathways. With aromatic rings that are easily reduced, this is a common mechanism, because the benzene ring can delocalize the radical anion. The radical chain mechanism is referred to as SrnI, (substitution, radical-nucleophilic, unimolecular). An example is shown in Eq. 10.118. 

Electron pushing for the SrnI mechanism for aromatic substitution. 

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