ORGANIC CHEMISTRY Chapter 21 21 11A Nucleophilic Aromatic Substitution by addition-Elimination The Sar mechanism o Nucleophilic substitution can occur when strong electron-withdrawing groups are ortho or para to the halogen atom NO-NO2一CF3=CRCN CO2H -SO3 Br -I-CO2 -C6H5 Department of Chemistry, Xiamen UniversityORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 21 21.11A Nucleophilic Aromatic Substitution by Addition-Elimination: The SNAr Mechanism Nucleophilic substitution can occur when strong electron-withdrawing groups are ortho or para to the halogen atom. N2 N NO NO2 CO2H CF3 CR CN O SO3 Cl Br I CO2 C6H5