Lecture 14 - deactivating o/p-directors A) Deactivate all...

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1 Reading for Friday ± Finish Chapter 18 Third ARIS Quiz ± Available Today ± Due at 11:59 pm, Sunday, Feb. 27 ± Two attempts; Score will be average of the two attempts. Mon. 6:00-7:30 pm MAL 3092 Tues. 2:30-4:00 PM MAL 2007 Wed. 5:00-6:30 PM MAL 2001 Thurs. 9:30-10:50 AM MAL 1003 Sat. 11:30 AM-1:00 PM MAL 2007 PLUS Sessions Chapter 18 Electrophilic Aromatic Substitution Effect of Substituents on Rate (Review) The Hammond Postulate in action, yet again! EDG’s stabilize carbocation intermediate and the TS leading to it. They INCREASE rate of EAS EWG’s destabilize carbocation intermediate and the TS leading to it. They DECREASE rate of EAS Substituent Directing Effects (Review) EDG’s are o/p -directors. Substituent provides extra stabilization to the carbocation intermediate resulting from ortho or para attack. Most EWG’s are meta -directors. Meta attack avoids placing the (+) charge on the carbon with the substituent.
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2 The Halogens: The only
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Unformatted text preview: deactivating o/p-directors A) Deactivate all ring positions (inductive withdrawal dominates over resonance donation) B) Are o/p-directors because they can stabilize resulting intermediates by resonance Fig. 18.7: Effect of substituents on benzene reactivity Limitations in EAS of Substituted Benzenes (18.10) A) Polyhalogenation of strongly activated rings (OH, OR, NH 2 , NR 2 ) B) Limitations in FC reactions i) EWGs prevent reaction ii) NH 2 groups prevent reaction iii) Polysubstitution a problem in FC alkylations Another key limitation of Friedel-Crafts Reactions CO 2 H and CHO cannot be added by FC acylation! Synthesis of Benzene Derivatives (18.12) You have already seen how to prepare some monosubstituted benzene derivatives via EAS If more than one substituent, synthetic strategy must take directing effects into account...
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This note was uploaded on 10/24/2011 for the course CHEMISTRY 623 taught by Professor Benson during the Spring '11 term at Kansas.

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Lecture 14 - deactivating o/p-directors A) Deactivate all...

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