Aldehyde chemical structure. Image credit: Flickr
Aldehyde chemical structure. Image credit: Flickr

An aldehyde is a part of an organic chemical compound class (also includes ketones) that has a carbonyl group, meaning a carbon atom is double bonded to an oxygen atom. A ketone and carboxylic acid also have a carbonyl group. However, unlike ketones, an aldehyde also has one or a couple of hydrogen atoms individually bonded to the carbonyl group. The aldehyde molecule could vary in size and can be long molecules that comprise carbon atoms inter-attached and also attached to hydrogen atoms. It’s believed the name “aldehyde” is derived from alcohol dehydrogenated.

Aldehyde is an electrophile, thanks to the carbonyl carbon’s positivity. The carbonyl carbon is marginally positive because of the double bond with the electronegative oxygen. An electrophile loves electrons, or it attracts electrons from nucleophiles. Nucleophiles are molecules that can give electrons to make a covalent bond. In this magnetic relationship, an electrophile is positive and nucleophile negative.


Aldehyde is an organic compound that chemically comprises a carbon, hydrogen and oxygen atom. The carbon and the oxygen atom have a double bond between them, which is referred to as carbonyl (C=O) group. An aldehyde must have a hydrogen atom, otherwise it would cease to be an aldehyde. There’s a single bond between the hydrogen and carbon atom, and the carbon has another single bond which could be another hydrogen atom or a group of atoms, called the R group. An R group could be a bunch of carbons or, at times, other elements. An R group’s identity is unknown except if it’s clearly mentioned.

Making Aldehydes

An aldehyde can be made using a range of chemical reactions. For instance, primary alcohol can be oxidized to make aldehyde. The aldehyde made courtesy primary alcohol oxidation can be further oxidized into a carboxylic acid, with acidified potassium dichromate functioning as the oxidizing agent. Since there’s a hydrogen atom involved, an aldehyde easily oxidizes, which means it can interact with oxygen. To prevent aldehyde further oxidizing into carboxylic acid, the aldehyde can be distilled or separated from the mixture quickly post its formation.

Similarly, hydroxyl group can be added to alkyne to make aldehyde. Also, acid chloride, ester, and nitrile can be subjected to chemical reactions to form aldehydes. 

Aldehyde Examples

There are different aldehydes and their basic structures change accordingly. For example, formaldehyde, acetaldehyde, propionaldehyde, etc. are forms of aldehydes. The most basic aldehyde comprise a carbonyl group that has two hydrogen atoms attached individually.


Glucose contains aldehyde, so do many synthetic and natural hormones. Aldehyde has a sweet, distinct smell. This explains why almonds have a sweet aroma, and there’s distinctness in cinnamon odor. Both comprise aldehydes, but in different forms. For example, benzaldehyde is the aldehyde in almonds and cinnamon has an aldehyde variant called cinnamaldehyde. The distinct smell also means aldehydes get used as solvents and ingredients in perfume, and also assist in the making of pharmaceuticals and dyes. Certain aldehydes also participate in physiological processes.