enantiomersmolecules

Enantiomers are a pair of molecules that are non-superimposable mirror images of each other. They arise when a molecule is chiral, typically because it contains a stereogenic center—often a carbon atom bonded to four different substituents. Enantiomers share most physical properties in an achiral environment, such as identical boiling points and densities, but they interact differently with chiral substances and with polarized light.

Optical activity is a hallmark of enantiomers: each enantiomer rotates plane-polarized light in opposite directions. The extent and direction of rotation are described by the specific rotation of each enantiomer. In stereochemical nomenclature, configurations at stereocenters are designated using the Cahn–Ingold–Prelog rules as R or S; the enantiomer is the mirror image with the opposite configuration at all stereocenters (for a single center, opposite of the original).

Enantiomers can also arise from axial or helical chirality, where the molecule’s overall three-dimensional arrangement, rather than a single stereocenter, creates chirality. In biology, enantiomers often have different effects because biological targets are themselves chiral. Many drugs are chiral, and one enantiomer may be more active or carry distinct side effects compared with its mirror image. A racemate is a 1:1 mixture of enantiomers, which may have different pharmacological properties than a pure enantiomer.

Methods to obtain or separate enantiomers include enantioselective synthesis, chiral resolution, and separation by chiral chromatography or crystallization using resolving agents. Lactic acid and amino acids are common examples illustrating naturally occurring enantiomeric forms.