Stereogenico

Stereogenico, or stereogenic in English, is a term used in chemistry to describe a feature of a molecule that can give rise to stereoisomerism. In practice, stereogenicity refers to the ability of a molecule to exist as distinct stereoisomers, such as enantiomers and diastereomers, that are not superimposable.

The most common stereogenic feature is a stereogenic center: an atom—most often carbon—bonded to four different substituents. Such a center can adopt two configurations, designated R and S, which correspond to non-superimposable mirror images. The assignment of these configurations follows the Cahn-Ingold-Prelog priority rules.

Stereogenicity can arise in other ways besides a classic carbon center. Atoms other than carbon can act as stereogenic centers under suitable constraints (for example, certain nitrogen, sulfur, or phosphorus environments). Other forms of stereogenicity include axial chirality (atropisomerism), planar chirality, and helical (axial) chirality. A site that can become stereogenic through a single modification is described as prochiral.

When a molecule contains multiple stereogenic centers, a range of stereoisomers is possible, including pairs of enantiomers and sets of diastereomers. Some molecules with stereogenic centers may be meso, possessing internal symmetry that renders them achiral despite having stereogenic elements.

Stereogenico is a fundamental concept in stereochemistry, influencing physical properties such as optical activity and, critically, biological activity, since enantiomers can interact differently with chiral environments such as enzymes and receptors. Examples include 2-butanol (one stereogenic carbon) and tartaric acid (two stereogenic centers, with a meso form).