Q1(d). Amination through a benzyne

Answer in brief

A is 4-methylbenzyne (the appropriately numbered methyl aryne); B and C are p-toluidine and m-toluidine.

Key points

• Amide removes an H ortho to bromine. Elimination of bromide gives an aryne bond between the original Br-bearing carbon and an adjacent ring carbon.
• Amide can add at either end of the aryne. Attack at the former Br carbon followed by protonation gives p-toluidine.
• Attack at the adjacent carbon followed by protonation gives m-toluidine. Liquid ammonia supplies the proton and regenerates amide.
• The positional mixture supports elimination–addition rather than a single ipso substitution.