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Chapter 23 Chem 233 (1)

Chapter 23 Chem 233 (1) - CARBONYL CONDENSATION...

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CARBONYL CONDENSATION CONDENSATION REACTIONS
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CARBONYL CONDENSATION REACTIONS Aldol Reaction Dehydration of Aldol Products Intramolecular Aldol Reaction Claisen Condensation Reaction Intramolecular Claisen Condensation Michael Reaction Stork Enamine Reaction Robinson Annulation Reaction
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General Mechanism of Carbonyl Condensation One carbonyl partner with an alpha hydrogen atom is converted by base into its enolate ion. O C R C H OH
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C O C C O R : .. .. R C O C OH 2 C O : : : Electrophilic Acceptor Nucleophilic Donor This enolate ion acts as a nucleophilic donor and adds to the electrophilic carbonyl group of the acceptor partner
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Protonation of the tetrahedral alkoxide ion intermediate gives the neutral condensation product. OH 2 R C C C OH -OH O + New C-C Bond
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ALDOL REACTION occurs between two aldehyde or ketone molecules with a catalytic base reaction can occur between two components that have alpha hydrogens reversible condensation reaction two highlights: enolate formation and nucleophilic attack at a carbonyl carbon Aldol products are: alpha-ß-unsaturated aldehydes/ketones and ß-hydroxy aldehydes/ ketones
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Mechanism of the Aldol Reaction HO : H C H H C O H Base removes an acidic alpha hydrogen from one aldehyde molecule, yielding a resonance- stabilized eno- late ion.
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C O CH 3 H : : O H + 2 C H H C H O .. CH 3 C H O C HH H O C H : : - .. The enolate ion attacks a second aldehyde molecule in a nucleophilic addition reaction to give a tetrahedral alkoxide ion intermediate.
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H O 2 C O C H C C H H H H O H H O 3 + - : Protonation of the alkoxide ion intermediate yields neutral aldol product and regenerates the base catalyst.
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Dehydration of Aldol Products: Synthesis of Enones ß-hydroxy aldehydes and ß-hydroxy ketones formed in aldol reactions can be easily dehydrated to yield conjugated enones Dehydration is catalyzed by both acid and base Reaction conditions for dehydration are only slightly more severe than for condensation Conjugated enones are more stable than nonconjugated enones
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C O C H C OH OH Base-catalyzed C O C C OH : : - ..
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