The document provides information on various types of condensation reactions, including aldol condensation, Claisen condensation, Knoevenagel condensation, benzoin condensation, and crossed aldol condensation. It discusses the mechanisms of these reactions, which involve a nucleophilic species (enolate or active hydrogen compound) attacking a carbonyl carbon to form a new carbon-carbon bond and water. Common reactants include esters, aldehydes, ketones, and acids or bases to catalyze enolate formation. Condensation reactions are important in biological processes like peptide bond formation and fatty acid biosynthesis.

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2. Condensation
 A condensation reaction is a class of organic addition reaction that
typically proceeds in a step-wise fashion to produce the addition
product, usually in equilibrium, and a water molecule (hence named
condensation).
 It is a versatile class of reactions that can occur in acidic or basic
conditions or in the presence of a catalyst.
 This class of reactions is a vital part of life as it is essential to the
formation of peptide bonds between amino acids and the biosynthesis
of fatty acids.

3. Many variations of condensation reactions exist, common examples include the aldol
condensation, Claisen condensation, Knoevenagel condensation, and the Dieckman
condensation (intramolecular Claisen condensation).
A simple example is the condensation of two amino acids to form a peptide. This
reaction example is the reverse of hydrolysis, which splits a chemical entity into two
parts through action from the polar water molecule, which itself splits into hydroxide
and hydrogen ions.
Idealized scheme showing condensation of two amino acids
to give a peptide bond.

4. Aldol condensation
 An enolate 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.

5. Mechanism of the base-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.

7. Crossed Aldol Condensation
 The condensation reaction between two different molecules of an
aldehyde or ketone in a protic solvent such as water or alcohol
constitutes the crossed aldol reaction. When condensation is
between two different carbonyl compounds, it is called crossed aldol
condensation.

8. Knoevenagel condensation
 Knoevenagel condensation is nucleophilic addition of an active
hydrogen compound to a carbonyl group followed by a dehydration
reaction in which a molecule of water is eliminated (hence
Condensation). The product is often an alpha, beta conjugated enone.
 Knoevenagel reaction is a modification of Aldol condensation reaction.
 The active hydrogen compound used should be of the form Z-CH2-Z or
Z-CHR-Z where Z is an electron withdrawing group.

11. Claisen condensation
 The Claisen condensation reaction is an organic coupling reaction that
results in the formation of a C-C bond between either a single ester and
one carbonyl compound or between two esters.
 The reaction proceeds when a strong base is present and the product of
the reaction is a beta-keto ester or a beta-diketone.

12. MECHANISM OF Claisen condensation
 Step 1: Enolate formation
The mechanism of Claisen condensation begins with the formation of
the ester enolate ion.
The ester is first deprotonated in the α position to form a resonance-
stabilized enolate.
 Step 2: Nucleophilic attack
Then this enolate function as a nucleophile and attacks another
molecule of the ester, forming a tetrahedral intermediate.
 Step 3: Removal of leaving group
In the next step, the tetrahedral intermediate expels the leaving group
to reform a carbon-oxygen double bond.

15. Benzoin condensation
INTRODUCTION:-
 The benzoin condensation is an addition reaction involving two aldehydes.
 The reaction occur between aromatic aldehydes or glyoxals.
 The benzoin condensation was reported in 1832 by Justus von liebig and Friedrich
wohler during their research on bitter almond oil.
 The catalytic version of the reaction involving cyanide was developed by Nikolay
Zinin in the late 1830s.
 This is a reversible reaction.
REACTION:-
When we heated two molecule of benzaldehyde with Alcoholic KCN
then Benzoin is obtained.

16. Reaction Mechanism
The mechanism of benzoin condensation reaction occur in following steps:-
1. In this step, the cyanide ion react with 1st molecule of benzaldehyde and
form Carbanion.
2. In this step, this carbanion reacts with 2nd molecule of benzaldehyde and
form intermediate compound.
3. In this step, proton transfer and elimination of the cyanide ion affords
Benzoin as a product.

18. QUESTIONS
 Condensation reaction always results in the formation of complex
sugar (disaccharide or polysaccharide) and which of the following?
a) amino acids
b) lipids
c) water
d) maltose
 In which condensation an enol or an enolate ion reacts with a carbonyl
compound to form a β-hydroxyaldehyde or β-hydroxyketone (an aldol
reaction), followed by dehydration to give a conjugated enone
happens?
a) Aldol condensation
b) Claisen reduction
c) Henry condensation
d) Knoevenagel condensation

19.  Condensation reaction is the reverse of which of the following
reaction?
a) lock and key hypothesis
b) oxidation
c) hydrolysis
d) glycogen formation
 Which combination of carbonyl compounds gives phenyl vinyl ketone
by an aldol condensation?
a) Acetophenone and ketone
b) Acetophenone and aldehyde
c) Benzaldehyde and aldehyde
d) Benzaldehyde and ketone

20. SUMMARY
 The Claisen condensation is the ester analogue of the Aldol condensation.
 Reagents : most commonly the base would be the alkoxide, R'O-
 The reaction involves an ester enolate reacting with another molecule of the
ester.
 Remember enolates are good nucleophiles and the ester carbonyl C are
electrophilic.
 Reagents : commonly a base such as NaOH or KOH is added to the aldehyde.
 The reaction involves an aldehyde enolate reacting with another molecule of
the aldehyde.
 Remember enolates are good nucleophiles and carbonyl C are good
electrophiles.
 Since the pKa of an aldehyde is close to that of NaOH, both enolate and
aldehyde are present simultaneously.
 The products of these reactions are β-hydroxyaldehydes or aldehyde-
alcohols = aldols.

21.  https://byjus.com/chemistry/aldol-
condensation/#:~:text=the%20aldol%20reaction.-
,Crossed%20Aldol%20Condensation,is%20called%20crossed%20aldol
%20condensation.
 https://www.chemistrylearner.com/knoevenagel-
condensation.html#:~:text=Some%20examples%20are%20diethyl%20
malonate,)%20%5B1%2D5%5D.&text=The%20history%20of%20this%2
0reaction,by%20German%20chemist%20Emil%20Knoevenagel.
 http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch21/ch21-3-
1.html#:~:text=Note%20that%20the%20product%20is,shown%20belo
w%20in%20two%20representations.
 https://www.chemistrylearner.com/benzoin-
condensation.html#:~:text=The%20benzoin%20condensation%20is%2
0the,is%20that%20of%20a%20ketone.&text=A%20cyanide%20ion%20
usually%20catalyzes%20benzoin%20condensation.

22. THANK YOU