1. 1 Benzyne Mechanism Reactant is halobenzene with no electron- withdrawing groups on the ring. Use a very strong base like NaNH 2. =>

2. 2 Benzyne Intermediate =>

3. 3 Chlorination of Benzene Addition to the benzene ring may occur with high heat and pressure (or light). The first Cl 2 addition is difficult, but the next 2 moles add rapidly. The product, benzene hexachloride, is an insecticide. =>

4. 4 Catalytic Hydrogenation Elevated heat and pressure is required. Possible catalysts: Pt, Pd, Ni, Ru, Rh. Reduction cannot be stopped at an intermediate stage. =>

5. 5 Birch Reduction: Regiospecific A carbon with an e - -withdrawing group is reduced. A carbon with an e - -releasing group is not reduced. =>

6. 6 Birch Mechanism =>

7. 7 Side-Chain Oxidation Alkylbenzenes are oxidized to benzoic acid by hot KMnO 4 or Na 2 Cr 2 O 7 /H 2 SO 4. =>

8. 8 Side-Chain Halogenation Benzylic position is the most reactive. Chlorination is not as selective as bromination, results in mixtures. Br 2 reacts only at the benzylic position. =>

9. 9 S N 1 Reactions Benzylic carbocations are resonance- stabilized, easily formed. Benzyl halides undergo S N 1 reactions. =>

10. 10 S N 2 Reactions Benzylic halides are 100 times more reactive than primary halides via S N 2. Transition state is stabilized by ring. =>

11. 11 Reactions of Phenols Some reactions like aliphatic alcohols: phenol + carboxylic acid  ester phenol + aq. NaOH  phenoxide ion Oxidation to quinones: 1,4-diketones. =>

12. 12 Quinones Hydroquinone is used as a developer for film. It reacts with light-sensitized AgBr grains, converting it to black Ag. Coenzyme Q is an oxidizing agent found in the mitochondria of cells. =>

13. 13 Electrophilic Substitution of Phenols Phenols and phenoxides are highly reactive. Only a weak catalyst (HF) required for Friedel- Crafts reaction. Tribromination occurs without catalyst. Even reacts with CO 2. =>