Ch. 22 - Condensation ChemistryWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins
Johnny Betancourt

The Claisen condensation is a base-catalyzed reaction between an ester and another carbonyl compound producing a beta-keto ester or beta-diketone as the product.


Overview

In a Claisen condensation, just like in other condensation reactions, an enolate attacks the electrophilic carbonyl carbon of a second molecule. What differentiates it from other condensation reactions is that it involves two molecules, at least one of which is an ester.

Enolate formation

Enolate-formation-with-NaOEtEnolate-formation-with-NaOEt

So, how do we actually form an enolate? We have to deprotonate the alpha-carbon of a carbonyl by using a strong base like sodium ethoxide or sodium amide. Remember that alpha-carbons are much more acidic than standard sp3-hybridized carbons!


Claisen condensation

Enolate-attack-on-esterEnolate attack on ester

Here we have the reaction between a ketone and ester. The stabilized anion (the enolate) attacks the electrophilic carbonyl through a nucleophilic acyl substitution mechanism and the alkoxide is eliminated. If our enolate were a ketone or aldehyde, we'd end up with a beta-diketone (two ketones separated by a carbon); if our enolate were an ester, we'd end up with a beta-keto ester (ketone and ester with a carbon between them). 

The reaction between a ketone and aldehyde (or any combination of those) is called an aldol condensation—so named because the nucleophilic addition forms an alcohol. 


Dieckmann condensation

The Dieckmann condensation is basically an intramolecular Claisen condensation that forms a cyclic beta-keto ester or beta-diketone. In this example, the 2 alpha-hydrogens in blue and green are entirely equivalent since the molecule is symmetrical. Dieckmann-condensationDieckmann Condensation



Johnny Betancourt

Johnny got his start tutoring Organic in 2006 when he was a Teaching Assistant. He graduated in Chemistry from FIU and finished up his UF Doctor of Pharmacy last year. He now enjoys helping thousands of students crush mechanisms, while moonlighting as a clinical pharmacist on weekends.