Aldol Condensation

Aldol Condensation can be defined as an organic reaction in which enolate ion reacts with a carbonyl compound to form β-hydroxyketone or β-hydroxyaldehyde, followed by a dehydration to give a conjugated enone. Aldol Condensation plays a vital role in the organic synthesis, creating a path to form carbon-carbon bonds.

Aldol Condensation

General Aldol Condensation Reaction

One of the common examples for base-catalyzed aldol condensation is stated below in which catalyst generally used is hydroxide ion.

aldol condensation reaction

Mechanism of Aldol Condensation

    1. In reverse order, The hydroxide ion deprotonates the aldehyde.

Mechanism of Aldol Condensation

    1. Here Enolate ion 1 adds to the unreacted aldehyde.

Enolate ion 1 adds to the unreacted aldehyde

    1. Alkoxide ion 2 is protonated by water.

Alkoxide ion 2 is protonated by water

    1. A small amount of aldol is converted into enolate ion (4) by hydroxide ion.

aldol converted into enolate ion (4) by hydroxide ion

    1. Here Enolate Ion(4) loses a hydroxide ion.

Enolate Ion(4) loses a hydroxide ion

Step 1 to step 3 illustrates aldol reaction.

Types of Condensation

It is important to differentiate aldol condensation from various reactions of carbonyl compounds.

  • In a case of Perkin reaction, enolate generated by anhydride is aromatic.
  • A Claisen condensation contains 2 ester compounds.
  • A Henry reaction contains an aliphatic nitro compound and an aldehyde.
  • Dieckmann condensation contains 2 ester groups present in the same molecule, which produces cyclic molecule.
  • In Japp–Maitland condensation, water is removed by nucleophilic displacement.

Sample Questions:

Some frequently asked questions in aldol condensation reaction that may help you in exam preparation are as follows:

Question 1: What is aldol condensation?

Answer: When aldehydes and ketones having at least one α-hydrogen are treated with dilute alkali (which act as a catalyst) they form β-hydroxyaldehydes (aldol) or β-hydroxyketones (ketol) respectively. This reaction is known as aldol condensation.

aldol condensation

Question 2: Explain the mechanism of aldol condensation.

Answer: Aldol condensation is an organic reaction in which an enolate ion reacts with carboxyl compound in order to form a β– hydroxyaldehyde or β– hydroxyketone.

  1. Hydroxide functions as a base and therefore moves the acidic a-hydrogen producing the reactive enolate ion. This reaction can be seen as an acid-base reaction.
  2. The aldehyde is attacked at the electrophilic carbonyl carbon by the nucleophilic enolate ion. This attack is a nucleophilic addition reaction and gives alkoxide intermediate.
  3. The alkoxide deprotonates water molecule, thereby producing hydroxide and the β–hydroxyaldehyde.

Which reference books can be followed to prepare for aldol condensation?

Answer: For studying aldol condensation one can follow the NCERT chemistry textbook part-2 for class 12th. The chapter named ‘Aldehydes, Ketones and Carboxylic acids’ in this book contains this process. For a better understanding of this concept, use the book Organic Chemistry by Morrison & Boyd or reference books such as Organic Chemistry written by Solomons & Fryhle. Solving previous year JEE papers will also be an added advantage on this topic.


Practise This Question

Arrange F, Cl, O, and N in the decreasing order of electronegativity.