Aldehydes and Ketones

Aldehydes and ketones contain a carbonyl group (>C=O), and are collectively called carbonyl compounds.

Some other examples of carbonyl compounds are : R-COOH (Carboxylic acid), R-COX (Acid halide), R-COOR' (Ester) etc.


In aldehydes, one end of the carbonyl group is attached to an alkyl (or aryl) group and the other is to a hydrogen atom.

Example of aldehydes
Aromatic Aldehyde example

Here R and Ar represent alkyl and aryl groups respectively. In condensed structural formulae, the carbonyl group of an aldehyde is represented as −CHO.

In formaldehyde (HCHO), the carbonyl group is attached to two hydrogen atoms instead of one hydrogen and one alkyl group.


In ketones, both the ends of carbonyl group are attached to alkyl or aryl groups.

Example of Ketones
Examples of aromatic ketones
Ketones examples

Important Points Regarding Carbonyl Groups

Nomenclature of Aldehydes and Ketones

Rules for naming aldehydes and ketones are discussed in nomenclature of aldehydes and ketones. If you want to learn nomenclature from the very beginning, start from nomenclature introduction.