Aldehyde
Definition and meaning of Aldehyde in chemistry.
An aldehyde is an organic compound with a carbonyl group bonded to at least one hydrogen atom. Its general structure is written as R-CHO. Aldehydes react easily and are readily oxidized into carboxylic acids.
In more detail
The aldehyde group has a carbon atom double bonded to an oxygen atom and single bonded to a hydrogen atom. This group usually sits at the very end of a carbon chain. Because of this terminal position, aldehydes are more reactive than ketones, which are their close chemical cousins.
In an aldehyde, both the hydrogen atom and the carbonyl carbon are open to attack. The hydrogen can be removed during oxidation, and the carbon can be attacked by electron rich molecules called nucleophiles. Aldehydes occur naturally in many places.
They show up in essential oils, plant extracts, and as temporary products inside the metabolic pathways of living cells. Industry relies heavily on aldehydes too. They serve as starting materials for making polymers, resins, pharmaceuticals, dyes, and many other organic compounds used every day.
Their high reactivity is exactly what makes them so useful as chemical building blocks. Many fruits and flowers get part of their characteristic smell from small amounts of natural aldehydes. Vanillin, the compound responsible for vanilla's flavor and smell, is itself an aromatic aldehyde.
A simple lab test called the Tollens test uses a silver mirror reaction to detect aldehydes. Ketones do not react the same way. This test helps chemists tell the two functional groups apart without needing advanced instruments.
Key facts
| Field | Organic Chemistry |
|---|---|
| General formula | R-CHO |
| Common examples | Acetaldehyde (CH3CHO) and formaldehyde (HCHO) |
| Functional group | Carbonyl (C=O) bonded to at least one hydrogen atom |
| Reactivity | Easily oxidized to carboxylic acids |
Acetaldehyde (CH3CHO) forms naturally during alcohol fermentation. It also serves as a key starting material for making acetic acid and acetic anhydride. Both are used to produce several polymers found in everyday consumer products.
Frequently asked questions
How do aldehydes differ from ketones?
Aldehydes have the carbonyl group at the end of the carbon chain, bonded to one hydrogen atom. Ketones have the carbonyl group in the middle of the chain, bonded to two carbon atoms instead.
What is formaldehyde?
Formaldehyde (HCHO) is the simplest aldehyde. It is widely used as a disinfectant, a preservative, and a starting material for making resins and polymers.
Why are aldehydes so reactive?
The carbonyl carbon in an aldehyde is easily attacked by electron rich molecules, and the attached hydrogen atom is easily removed during oxidation. Both features make aldehydes more reactive than many other organic compounds.
Related terms
Sources & references
See our sources and editorial standards.