Chapter 16 September 16

Chapter 16 September 16 - elimination : 5...

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1 Nucleophilic Aromatic Substitution Example: What is the propable mechanism for this reaction? S N 1? S N 2?
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2 Neither route seems plausible: Let's explain the mechanism by looking at the reaction requirements: 1.) The aromatic ring must be electron deficient
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3 2.) Why? An electron withdrawing substituent must be present in either an ortho or para position to the leaving group (Cl ­ )
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4 The Actual Mechanism for Nucleophilic Aromatic Substitution: Electrophilic substitutions are favored by electron donating substituents Nucleophilic substitutions are favored by electron withdrawing substituents Groups that deactivate aromatic rings for electrophilic substitution actually activate rings for nucleophilic substitution Meta directing groups in electrophilic substitution become ortho/para directing groups in nucleophilic substitution reactions Addition followed by
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Unformatted text preview: elimination : 5 Elimination/Addition Reactions and the Benzyne Intermediate: Without the high temperature and high pressure this reaction does not take place 6 Evidence to support the formation of a benzyne intermediate: The benzyne formed is significantly more reactive (unstable) than a conventional triple bond 7 Practice Problems: 8 Oxidation of Aromatic Compounds: Examples: Benzene rings are inert to strong oxidizing reagents such as KMnO 4 and Na 2 Cr 2 O 7 The presense of an aromatic ring, however, causes the alkyl side chains to be readily converted to carboxylic acids 9 Oxidation Reaction Limitations: Example: Practice Problems: The intermediate of this side chain oxidation requires the formation of a benzylic radical (radical on the carbon adjacent to the aromatic ring)...
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Chapter 16 September 16 - elimination : 5...

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