:Hydroxybutyric acid
{{multiple image
| align = right
| direction = vertical
| width = 200
| image1 = 2-hydroxybutyric acid.png
| alt1 = α-hydroxybutyric acid structure
| caption1 = Skeletal formula of α-hydroxybutyric acid
| image2 = beta-Hydroxybutyric acid-2D-skeletal.svg
| alt2 = β-hydroxybutyric acid structure
| caption2 = Skeletal formula of β-hydroxybutyric acid
| image3 = 4-Hydroxybutansäure - 4-Hydroxybutanoic acid.svg
| alt3 = γ-hydroxybutyric acid structure
| caption3 = Skeletal formula of γ-hydroxybutyric acid
| image4 = 2-HydroxyisobutyricAcid.svg
| alt4 = α-hydroxyisobutyric acid structure
| caption4 = Skeletal formula of 2-hydroxyisobutyric acid
| image5 = 3-Hydroxyisobutyric acid.png
| alt5 = β-hydroxyisobutyric acid structure
| caption5 = Skeletal formula of 3-hydroxyisobutyric acid
}}
Hydroxybutyric acid is a group of four-carbon organic compounds that have both hydroxyl and carboxylic acid functional groups.{{Ullmann |doi=10.1002/14356007.a13_507|title=Hydroxycarboxylic Acids, Aliphatic |year=2000 |last1=Miltenberger |first1=Karlheinz |isbn=3527306730}} They can be viewed as derivatives of butyric acid. The carboxylate anion and the esters of hydroxybutyric acids are known as hydroxybutyrates. β-hydroxybutyric acid is relevant to human health as it is a member of a class of products of fatty acid oxidation referred to as ketone bodies.
The isomers are distinguished by the distance between the two functional groups and the branching.
- alpha-Hydroxybutyric acid (2-hydroxybutyric acid)
- beta-Hydroxybutyric acid (3-hydroxybutyric acid)
- gamma-Hydroxybutyric acid (4-hydroxybutyric acid, GHB)
- 2-hydroxyisobutyric acid
- 3-hydroxyisobutyric acid