enantiomeer

Enantiomeer is the singular form used in Dutch and some other languages for one of the two stereoisomers that are non-superimposable mirror images of each other. In English, the standard term is enantiomer, and the concept is the same: a pair of molecules that share the same connectivity but are mirror images that cannot be superimposed.

Enantiomers arise in chiral molecules, typically when a stereogenic center is present, such as a carbon atom bonded to four different substituents. The two mirror images constitute an enantiomeric pair. They have identical physical properties in achiral environments (for example, melting points and boiling points) but interact differently with polarized light and with chiral surroundings. Each enantiomer rotates plane-polarized light in a specific direction, with one being dextrorotatory and the other levorotatory; the magnitude of rotation is measured as specific rotation.

In chiral environments, such as biological systems or chiral solvents, enantiomers can exhibit markedly different behavior, including distinct binding to enzymes or receptors, different pharmacological activities, and different sensory perceptions. The configuration around stereogenic centers can be described using R/S nomenclature by the CIP rules; for a single stereocenter, the two enantiomers have opposite configurations.

Separation and analysis often rely on formation of diastereomeric derivatives, chiral chromatography, or crystallization as diastereomeric salts. A racemate is an equal mixture of both enantiomers, which is optically inactive.

Examples include lactic acid and carvone, the latter of which has enantiomers with different odor notes. Enantiomeric purity is a crucial consideration in chemistry and drug development, because the two enantiomers can have very different biological effects.