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Aldol condensation
The aldol condensation reaction allows carbonyl compounds containing an α-hydrogen atom to undergo condensation. It is a reversible reaction that proceeds through an enolate intermediate formed when hydroxide deprotonates the α-hydrogen. The enolate then acts as a nucleophile that attacks the electrophilic carbonyl carbon of an aldehyde or ketone. Protonation of the resulting alkoxide forms the β-hydroxy aldehyde or ketone product. The reaction can join two different aldehydes or ketones in a crossed-aldol condensation that expands the synthetic possibilities.
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Aldol condensation requires a carbonyl compound with α-hydrogen; aldehydes and ketones without α-hydrogens do not undergo this reaction.
Aldol reaction involves nucleophilic addition of enolate to carbonyl. It has specific conditions and hydroxide as a base.
Condensation influenced by groups on carbonyls; can occur between various aldehydes/ketones, but products aren't isolated reliably.
Crossed-aldol reactions combine different aldehydes/ketones, creating β-hydroxy compounds crucial in biology and pharmaceuticals.
Presented by Akili Karuna.
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Aldol condensation
- 2. ALDOL CONDENSATION ispossible only when the carbonyl compound contains atleast one α-hydrogen atom.
- 3. Thus the followingAldehydes or ketones having no α-hydrogen atom do not undergo Aldol Condensation.
- 4. Some conditions regardingthe Aldol Reaction A reversible equilibrium OH is the base typically used in an aldol reaction. Aldol reactions can be carried out with either aldehydes or ketones. With aldehydes, the equilibrium favors products With ketones the equilibrium favors the starting materials.
- 6. Step 1: First,an acid-base reaction. Hydroxide functions as a base and removes the acidic a-hydrogen giving the reactive enolate. Step 2: The nucleophilic enolate attacks the aldehyde at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide. Step 3: An acid-base reaction. The alkoxide deprotonates a water molecule creating hydroxide and the β- hydroxyaldehydes or aldol product.
- 7. An enolate ionis the anion formed when an alpha hydrogen in the molecule of an aldehyde or a ketone is removed as a hydrogen ion. enolate ion
- 8. The alkoxide ionis the conjugate base of alcohols.
- 9. Alkoxide ion isprotonated by water.
- 11. The aldolcondensation is facilitated by-I groups on the carbonyl component and retarted by +I groups as described in CHзCHO and CHзCOCHз condensations. The condensation is readily reversible and the position of equilibrium is not always favorable to the product. Eg:
- 12. LIMITATIONS: Aldol products,as such,are not always isolated from the reaction mixture.eg:acetaldol readily forms a cyclic hemi-acetol. EXTENSIONS: Aldol condensation can occur between Two identical or different aldehydes Two identical or different ketones An aldehyde and a ketone
- 13. The Rgroups may be H, alkyl, or aryl. When the R groups in one molecule are different than those in the other, the reaction is called a crossed-aldol reaction. The ability to join different aldehydes and ketones together is what give this process its synthetic value. The name aldol condensation is also commonly used,especially in biochemistry,to refer to just the first stage of the process the aldol reaction itself as catalysed by aldolases.
- 14. In its usualform ,it involves the nucleophilic addition of a ketone enolate to an aldehyde to form a β-hydroxy ketone or aldol(aldehyde+alchohol), a structural unit found in many naturally occuring molecules and pharmaceuticals.
- 15.