Condensation Reaction
A condensation reaction is a type of chemical reaction in which two molecules combine to form a larger molecule with the simultaneous loss of a small molecule, most commonly water (H2O) but sometimes methanol, HCl, or ammonia. Condensation reactions are fundamental in the synthesis of polymers, esters, amides, and biological macromolecules including proteins, nucleic acids, and polysaccharides. The reverse process, in which the small molecule is reincorporated to break the bond, is called hydrolysis.
Key Formula
R-OH + HO-R' → R-O-R' + H2O (condensation to form ester or ether)
LaTeX: R\text{-OH} + HO\text{-}R' \rightarrow R\text{-O-}R' + H_2O
| Symbol | Meaning | Unit |
|---|---|---|
| R | Organic group (alkyl or aryl) | — |
| R' | Second organic group | — |
| H2O | Water molecule lost in the reaction | — |
Worked Example
Problem
Write the condensation reaction between ethanoic acid (CH3COOH) and ethanol (C2H5OH) in the presence of concentrated H2SO4 catalyst.
Solution
Step 1: Identify functional groups — carboxylic acid (–COOH) and alcohol (–OH). Step 2: In esterification (a condensation reaction), the –OH of the acid and the H of the alcohol combine to leave as water. Step 3: The remaining fragments bond: CH3CO– + –OC2H5 → CH3COOC2H5. Step 4: Full equation: CH3COOH + C2H5OH ⇌ CH3COOC2H5 + H2O Step 5: The product ethyl ethanoate is an ester; the reaction is reversible and driven forward by removing water.
Answer
Ethyl ethanoate (CH3COOC2H5) + water (H2O).
Types of Condensation Reactions and Their By-products
| Reaction Type | Reactants | Bond Formed | Small Molecule Lost | Product Class |
|---|---|---|---|---|
| Esterification | Carboxylic acid + Alcohol | Ester (C–O–C=O) | Water (H2O) | Ester |
| Amide formation | Carboxylic acid + Amine | Amide (–CO–NH–) | Water (H2O) | Amide/Peptide |
| Acetal formation | Aldehyde + Alcohol (×2) | Acetal (C(OR)2) | Water (H2O) | Acetal |
| Silyl ether | Silanol + Alcohol | Si–O–C bond | Water (H2O) | Silyl ether |
| Nylon-6,6 synthesis | Diamine + Diacid chloride | –NH–CO– (amide) | HCl | Polyamide |
| Aldol condensation | Two aldehydes/ketones | C–C bond + C=C | Water (H2O) | α,β-Unsaturated carbonyl |
Interactive Tools
Khan Academy — Condensation and Hydrolysis
Explains condensation and hydrolysis reactions with biological context.
Open ToolChemSpider — Ethyl Ethanoate
Structure and properties of the esterification product ethyl ethanoate.
Open ToolBrilliant.org — Condensation Reactions
Detailed notes on condensation reaction types and mechanisms.
Open Tool
Wikimedia Commons, CC BY-SA
Related Terms
Polymer
A polymer is a large macromolecule composed of many repeating structural units called monomers, linked together by covalent bonds through a process called polymerisation. Polymers can be natural (e.g., cellulose, proteins, DNA) or synthetic (e.g., polyethylene, nylon, PVC), and their physical properties are governed by chain length, branching, cross-linking, and monomer identity. They are indispensable in modern industry, biology, and materials science.
Peptide Bond
A peptide bond is a covalent amide linkage formed between the carboxyl group (–COOH) of one amino acid and the amino group (–NH2) of another, with the elimination of a water molecule in a condensation reaction. The resulting –CO–NH– bond has partial double bond character due to resonance delocalisation of the nitrogen lone pair into the carbonyl, making it planar and restricting rotation around the C–N bond. Peptide bonds are the primary covalent linkages in all protein chains.
Saponification
Saponification is the alkaline hydrolysis of a fat or ester, in which a triglyceride reacts with a strong base (typically NaOH or KOH) to produce glycerol and the sodium or potassium salts of fatty acids, commonly known as soap. The reaction is irreversible under alkaline conditions, unlike acid-catalysed esterification. Saponification is the chemical basis of soap manufacture and is widely studied as an example of nucleophilic acyl substitution in organic chemistry.
From Latin 'condensare' (to make dense or compact). The term 'condensation' was applied to organic reactions in the 19th century by chemists such as Adolph Wurtz and Emil Fischer, who noted that molecules combine while expelling a small, simple by-product — the reaction 'condenses' two species into one.