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Benzyne Mechanism

Two mechanisms have been proposed for nucleophilic aromatic substitution, one of which involves a benzyne as the intermediate and, therefore, is called benzyne mechanism.

eg:



mechanism:

Step 1:



Step 2:



Step 3:



Step 1 requires a very strong base.  Thus, for the benzyne mechanism to be operant, the medium must be very strongly basic.

see also SNAr mechanism