Cétones

Cétones are a class of organic compounds characterized by a carbonyl group (C=O) bonded to two carbon substituents, giving the general formula R-CO-R'. The carbonyl carbon is sp2-hybridized and the C=O bond is polar. If a hydrogen atom is attached to the carbonyl carbon, the compound is an aldehyde instead of a ketone.

Nomenclature and naming conventions distinguish ketones from aldehydes by the carbonyl’s location. The parent chain is chosen to include the carbonyl, and the suffix -one is used. The substituents on either side of the carbonyl are named as prefixes (e.g., 2-butanone, benzophenone). The common name format often uses two alkyl or aryl groups with the word “ketone,” such as dimethyl ketone (acetone).

Ketones are typically liquids or solids with polar, relatively high-boiling components. Acetone is a well-known, highly miscible solvent. In general, boiling points rise with molecular weight and branching. Ketones are reactive in carbonyl chemistry: they undergo nucleophilic addition to the carbonyl, can form enolates at the alpha position, and participate in reactions such as Grignard additions to give tertiary alcohols after hydrolysis. Aldol condensations between ketones yield β-hydroxy ketones and, after dehydration, α,β-unsaturated ketones.

Biochemistry and metabolism provide notable natural occurrences: ketone bodies (acetoacetate, β-hydroxybutyrate, acetone) are produced by the liver during fasting or carbohydrate restriction and used as energy sources by tissues; excessive production can lead to ketoacidosis. Industrially, ketones serve as solvents, intermediates, and monomers in synthesis and polymer chemistry.