- Aldol condensation is a reaction that occurs between two carbonyl compounds, such as aldehydes or ketones, in the presence of a base. This forms a β-hydroxy aldehyde or ketone. - The reaction involves the base deprotonating one of the carbonyl compounds to form an enolate ion. This acts as a nucleophile and attacks the carbonyl carbon of the other reactant. - After addition of water, an aldol or ketol product is formed containing both original R groups and a new C-C bond, along with an alcohol group.

1. A property of carobnyl
compounds having hydrogen at
α-carbon
ALDOL condensation

2. ALDOL condensation
• Aldol means aldehyde and alcohol groups on the same
molecule
• May occur between two aldehydes (aldols) or ketones
(ketols) in the presence of a catalytic base
• Reaction is only possible between two components
having α-hydrogen

3. ALDOL condensation
• Formation of aldols or ketols reactions are
reversible
• Mechanism: involves enolate formation
and nucleophilic attack at a carbonyl
carbon
• Aldols and ketols loose water in the
presence of an acid forming α-ß-
unsaturated aldehydes or ketones and ß-
hydroxy aldehydes or ketones

4. Aldol condensation
• Aldehydes containing α-hydrogen undergo self
addition in the presence of a base to form aldols
• For example
2 molecules of acetaldehyde condense to form
aldol haviving the name 3-hydroxy butanal

6. Mechanism
Step-1 One carbonyl partner with an alpha hydrogen atom is
converted by base into its enolate ion
O
C
R C
H
OH

7. C
O
C
C O
R
:
..
..
R
C
O
C
OH2
C
O:
: :
Electrophilic
Acceptor
Nucleophilic
Donor
Step 2 This enolate ion
acts as a nucleophilic and
adds to the electrophilic
carbonyl group of the
acceptor partner

8. Step 3 addition of water resulting a neutral
condensation product
OH2
R
C
C
C
OH -OH
O
+
New C-C Bond

9. 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.

10. C
O
CH3 H
: : OH+ 2
C
H
H
C
H
O
..
The enolate ion attacks
a second aldehyde
molecule in a
nucleophilic addition
reaction to give a
tetrahedral alkoxide ion
intermediate

11. H O2
Protonation of the alkoxide ion intermediate yields
neutral aldol product and regenerates the base
catalyst

12. Aldols loss water in the presence of
an acid forming α-ß-unsaturated
aldehydes
Heat/acid

13. Ketol condensation
• Like aldehydes, ketones having alpha
hydrogen condense to form ketols
For example
2 molecules of acetone condense to produce
4-hydroxy, 4-methyl, 2-pentanone

14. 4 methyl-3 pentene-2 one4-hydroxy, 4-methyl, 2-pentanone

15. Mixed aldol condensation
• If two different aldehydes condense, the
process is called mixed aldol condensation.
• For example
• Benzaldehyde and acetaldehyde condense
to form cinnamaldehyde