n with Arenediazonium 8ae总88n8Pa.ny ae2o o89 的aa Important Concepts 1. ion-benittihe s with a Nucloophilic Aromatic pso 秋射 三 4 5. 出 22 Important Concepts 6. o the aron stitution- up can be ed by 1313 Electrophilic Substitution with Arenediazonium Salts: Diazo Coupling 22-11 Arenediazonium ions are electrophilic (they are positively charged), although not very reactive in electrophilic aromatic substitution reactions. When the substrate is an activated arene, however, such as phenol or benzenamine, arenediazonium ions can undergo electrophilic aromatic substitution. This reaction is called diazo coupling, and it leads to highly colored compounds called azo dyes. Azo dyes used in the clothing industry usually contain sulfonic acid groups to impart water solubility and to allow the dye molecule to ionically attach itself to the textile polymer framework. 22 Important Concepts 1. Resonance Stabilization – benzylic radicals, cations and anions are stabilized by resonance of the resulting centers with a benzene π system. 2. Nucleophilic Aromatic Ipso Substitution – accelerates with: • Nucleophilicity of the attacking species • Number of electron-withdrawing groups on the ring (especially if ortho or para, to point of attack) 3. Benzyne – destabilized by strain at the sp￾hybridized carbons in the triple bond 4. Phenols – aromatic enols (undergoing reactions typical of the hydroxy group and the aromatic ring) 5. Cyclohexadienediones – and benzenediols function as redox couples. 22 Important Concepts 6. Vitamin E – and the highly substituted phenol derivatives BHA and BHT inhibit radical-chain oxidation of lipids. Vitamin C (antioxidant) is capable of regenerating vitamin E at cell membrane surfaces. 7. Arenediazonium Ions – furnish reactive aryl cations with a positive charge that cannot be delocalized into the aromatic ring. 8. Electrophilic Aromatic Substitution – the amino group can be used to direct electrophilic aromatic substitution, after which it can be replaced by diazotization and substitution, including reduction