Aromatic Compounds - PowerPoint PPT Presentation

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Aromatic Compounds

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  1. Aromatic Compounds

  2. Aromatic Systems are Characterized by Their Chemical Stability • Note the chemical stability of the aromatic systems to the reaction conditions in the following slides

  3. Note aromatic system’s stability toward hydrogenation

  4. Note aromatic systems’ stability toward strong reducing agent LiAlH4

  5. Note the (two) aromatic systems’ stability toward Br2

  6. Note the aryl iodide’s stability toward SN2 substitution (SN2 substitution occurs at the sp3 hybridized carbon)

  7. Note the aryl iodide’s stability toward the strong base (potassium tert-butoxide) used to effect elimination

  8. Reactions of Aromatic Systems: Electrophilic Aromatic Substitution

  9. The Friedel-Crafts Reaction

  10. Treatment of Aryl Halides with Extremely strong bases (amide anions, NaNH2, pKa of ammonia = 38) can cause substitution reactions… (note that the above table shows the conjugate acids only)

  11. But the mechanism involves a two-step process of elimination-addition.

  12. Treatment of aryl halides having strongly electron-withdrawing substituents (at the 2- and the 4-position) can also cause substitution reactions But…

  13. The mechanism involves addition-elimination.

  14. Reactions of Side Chains and Attached Functionality on Aromatic Compounds

  15. Treatment of amines with nitrous acid (HONO) generates diazonium salts

  16. The Sandmeyer Reaction Swiss chemist (1854-1922) after whom reaction is named

  17. Benzylic Positions Can be Selectively Oxidized (all the way to the carboxylic acid) by Potassium Permanganate

  18. The Clemmensen Reduction

  19. Hydrogenolysis of Benzyl Esters and Benzyl Ethers