Nucleophilic substitution in aromatic compounds is feasible in substrates bearing strong electron-withdrawing substituents positioned ortho or para to the leaving group. The reaction proceeds via two steps: the addition of the nucleophile and the elimination of the leaving group.
The reaction begins with an attack of the nucleophile on the carbon that holds the leaving group. This results in the delocalization of the π electrons over the ring carbons. The resonance interaction between the delocalized electron pair and the electron-withdrawing group further stabilizes the intermediate through the formation of Meisenheimer complexes. Finally, the electron-withdrawing group releases the electron back into the ring, facilitating the departure of the leaving group and restoring aromaticity.
