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Chemistry lectures : Condensation
The document summarizes key aspects of aldol condensation reactions. It describes how an enolate acts as a nucleophile in the reaction with the carbonyl carbon of a second carbonyl compound, forming a new carbon-carbon bond. The position of equilibrium depends on reaction conditions and substrates. The aldol product can undergo base-catalyzed dehydration to an alpha,beta-unsaturated carbonyl. Aldol reactions favor alpha-monosubstituted aldehydes and disfavor alpha,alpha-disubstituted aldehydes and ketones. Mixed aldol reactions between two different carbonyl compounds are also discussed, as well as the benzoin condensation reaction between two aromatic aldehydes
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Chemistry lectures : Condensation
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- 2. Aldol Condensation • Anenolate of one carbonyl (nucleophile) reacts with the carbonyl carbon (electrophile) of a second carbonyl compound resulting in the formation of a new C-C bond. H3C C H O acetaldehyde 2 CH2 C H O CHH3C OH 3-hydroxybutanal (-hydroxy aldehyde) + HO + HO
- 3. Mechanism of thebase-catalyzed aldol condensation • The position of the equilibrium for the aldol reaction is highly dependent on the reaction conditions, substrates, and steric considerations of the aldol product. Low temperature tends to favor the aldol product. • The aldol product can undergo base-catalyzed dehydration to an ,-unsaturated carbonyl. The dehydration is essentially irreversible. C C H O NaOEt EtOH R H H HC C O RH C CR HH HHO C C H O NaOEt EtOH R H R HC C O RR C CR HR HHO C C R O NaOEt EtOH R H H RC C O HR C CR HH RHO
- 4. • Aldol reactionsinvolving -monosubstituted aldehydes are generally favorable. • Aldol reactions involving -disubstituted aldehydes are generally unfavorable. • Aldol reactions involving ketones are generally unfavorable.
- 5. Mixed Aldol Reaction Aldolreaction between two different carbonyl compounds- C O H + C O CH3H3C NaOH, H2O C O CH3C C H H HHO
- 6. Benzoin Condensation • When2 moles of aromatic aldehydes react in the presence of KCN, an alpha hydroxyl ketone is obtained C O OH O H 2 CN 8.47
- 7. Mechanism for theBenzoin Condensation C CHO C H N CHO C N H O O CN OH H O OH O H B H B HH CHO C N CN +CN 8.48 8.49 8.50 8.47 :B B: