ABSTRACT
Aromatic molecules, like benzene, are exceptionally stable because of the ring with 4n+2 π electrons. As such, aromatic molecules do not undergo addition, which would disrupt aromaticity, but rather they react through addition reactions. In this chapter, aromatic substitution reactions – electrophilic aromatic substitution (EAS), nucleophilic aromatic substitution (SNAr), benzyne, and radical substitution – will be considered in detail. EAS reactions utilize Brønsted–Lowry or Lewis acids to generate highly electrophilic reagents that are attacked by benzene, as a nucleophile. This generates an arenium ion intermediate and the benzene ring is reformed by deprotonation. The regiochemical outcome of multiple EAS reactions is dictated by the stability of the arenium ion intermediate and whether groups can stabilize or destabilize the ion through inductive and delocalization effects. SNAr and benzyne substitution replace halogen atoms on the ring with strong nucleophiles and strongly basic nucleophiles, respectively. Finally, radical substitution reactions occur with phenyldiazonium (PhN2 +) salts.
