The aldol condensation reaction involves the reaction of two carbonyl compounds in the presence of a strong base to form a β-hydroxyaldehyde or β-hydroxyketone. The reaction proceeds through the formation of an enolate ion intermediate that acts as a nucleophile, attacking the carbonyl carbon of the other molecule. This forms a carbon-carbon bond between the α-carbon of the donor molecule and the carbonyl carbon of the acceptor molecule. The reaction allows for the facile synthesis of larger molecules from simple starting materials.

2.  In the presence of a strong base, two
different molecules of aldehyde or ketone
combine to form a β-hydroxyaldehyde or a
β-hydroxyketone.
 This reaction is called as the aldol
condensation.

3.  The enolate ion (carbanion) is the actual
nucleophilic reagent.
 The reaction breaks down to the following:
The α-carbon of the donor attaches itself to
the carbonyl carbon of the acceptor.

4. CH3 C
H
O CH3 C
H
O
CH2
C
H
O
CH2
C
H
O
+ _ _
..
_
acceptor
donor

5.  The carbonyl group plays two roles in this reaction:
 1. It provides a site for nucleophilic attack by the
enolate ion.
 2. It makes the a-hydrogens sufficiently acidic
to enable the formation of reasonable
concentrations of enolate ion.
 NOTE: There must be a-hydrogens in order to
undergo aldol condensation.
 Without a-hydrogens, the only possible reaction is
Cannizarro reaction

6.  If both carbonyl compounds have α-hydrogens, then
the donor and acceptor could be controlled.
 If one carbonyl compound that does not have α-
hydrogens is chosen, it can only act as an acceptor.
 Then, but adding the donor to a dilute solution of
acceptor, we can control the reaction to give only one
product.

7. C H
O
+
CH3 C H
O
NaOH
C CH2
OH
H
C H
O
- H2O
(spontaneously)
CH CH C H
O
CINNAMALDEHYDE

8.  Step 1: Deprotonation and formation of nucleophile.
• Step 2: Attack by nucleophile: Formation of alkoxide
ion.

9.  Step 3: Hydrolysis and formation of Aldol type product
Step 4: Intramolecular dehydration

10.  The aldol condensation is very useful in the
preparation of large molecules from simple starting
materials.
 In biosynthesis, where large molecules are products,
condensation reactions provide the only reasonable
route, since all of the starting materials are small
molecules containing only two or three carbons.
 In synthesis of insect repellants such as 2-Ethyl-3-
hydroxy hexanal

11. CH2 CH C H
O
OHO
P
OH
OO
CH2 C CH2 O P OH
OH
O O
O
CH2
CH C CH C CH2
O P OH
O
O
O
OH
OH
HOHO
P
OH
O O
+
Glyceraldehyde-3-phosphate
Dihydroxyacetone phosphate
Fructose-1,6-diphosphate
a
ALDOL
CONDENSATION
enzyme