Condensation reactions are reactions in which two molecules combine to form a larger molecule, producing a small molecule such as H2O as a byproduct. They typically form a new carbon-carbon bond and result from a nucleophilic enolate and an electrophilic carbonyl. 

P.S. Here is the 2-hour super-comprehensive version if you are not in a time crunch. 

Condensation Overview

There are a few varieties of condensation reactions, and all require those two pieces. Sometimes metal-complex catalysts are added, but luckily most undergrad Orgo classes focus on base-catalyzed mechanisms! You’ll likely see these reactions again later in carbohydrate chemistry or in Biology class.

So, how do we actually form an enolate? We have to deprotonate the alpha-carbon of a carbonyl. Remember that alpha-carbons are much more acidic than standard sp3-hybridized carbons! Let’s quickly go over three condensation reactions here:



Enolate Formation

A base is used to deprotonate the alpha-hydrogen. The type of condensation reaction the resulting enolate undergoes depends on what kind of electrophile is present. 

Aldol Condensation


Aldol Condensation

The aldol condensation reaction occurs between an enolate and an aldehyde to yield a beta-hydroxy ketone.

Claisen Condensation


Claisen Condensation

The Claisen condensation reaction involves an ester (or diester) and an enolate. It yields a beta-keto ester or a beta-diketone by displacing the acyl group through nucleophilic acyl subsitutition. The above reaction resulted in a beta-diketone.

Dieckmann Condensation


Dieckmann Condensation

The Dieckmann condensation reaction is an intramolecular reaction of a diester. The enolate forms on the alpha carbon of one carbonyl and then directly attacks the other. This forms a ring with a beta-keto ester.

Two things to note: 1) the products can undergo dehydration to form an enone (an alpha-beta unsaturated ketone) through an E1cB mechanism and 2) these reactions are reversible through hydrolysis! Let’s see what each of our products looks like after dehydration:


Dehydrated Condensation Products

Detailed Videos

There are plenty of different types of condensation reactions:

P.S. Congratulations! You just learned a form of polymerization! Carbonyl compounds can combine to form polymers like nylon through this mechanism!

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