Chapter 16 Templates -...

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1 Chapter 16: Reactions of Benzene and Its Derivatives No electrophilic addition reactions occur Undergo electrophilic aromatic substitution reactions (EAS) Due to a loss of aromatic stabilization energy Benzene pi electrons act as a lewis base (e ­ donor) Electrophilic species acts as a lewis acid (e ­ acceptor)
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2 General Reaction Summary:
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3 Reaction Energy Diagram : Generic Aromatic Electrophilic Substitution Resonance Stabilization of the Cationic Intermediate: .
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4 Halogenation (Bromination): Overall Reaction: Generation of the Electrophile: Mechanism: .
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5 Aromatic Chlorination and Iodination: Fluorine is too reactive. Monofluoro products are too problematic to make in this fashion
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6 Nitration Reaction: Generation of the Electrophile: Reduction of the Nitro Group (Amine Formation): Mechanism: .
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7 Sulfonation Reaction: Generation of the Electrophile: Alkali Fusion Reaction: Mechanism: . Sulfonation is favored in strong acid Reversible in hot, dilute aqueous acid (desulfonation)
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8 Aromatic Alkylation Reactions : The Friedel­Crafts Reaction Overall Reaction: Mechanism:
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9 Caveats and Limitations: Only alkyl halides (F, Cl, Br, I) can be used Cannot be performed on a benzene ring that has a strongly electron withdrawing group on it. Decrease the reactivity of the ring by decreasing the ring's nucleophilicity via electron withdrawal Amino groups will react with the Lewis acid so that no electrophilic species is generated Often result in multiple substitutions. Difficult to stop at single addition
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10 Caveats and Limitations (cont'd): Carbocation Rearrangement: Example (Hydride Shift):
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11 Carbocation Rearrangement: Example (Alkyl Shift): Caveats and Limitations (cont'd):
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This note was uploaded on 01/29/2012 for the course CHEM 234-54 taught by Professor Morrison during the Fall '09 term at University of Georgia Athens.

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Chapter 16 Templates -...

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