2. ALDOL CONDENSATION is possible
only when the carbonyl compound
contains atleast one α-hydrogen atom.
3. Thus the following Aldehydes or ketones
having no α-hydrogen atom do not undergo
Aldol Condensation.
4. Some conditions regarding the 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.
5.
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 ion is the anion formed when
an alpha hydrogen in the molecule of
an aldehyde or a ketone is removed as a
hydrogen ion.
enolate
ion
11. The aldol condensation 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 R groups 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 usual form ,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.
