enantiomeeri

Enantiomer (Finnish: enantiomeeri) refers to one of two stereoisomers that are non-superimposable mirror images of each other. These molecules are chiral and cannot be superimposed onto their mirror image, much like left and right hands. Enantiomers have identical physical properties in achiral environments, such as melting points and boiling points, and they often share identical spectroscopic characteristics, but they interact differently with polarized light and with other chiral substances or environments.

In stereochemistry, molecules with one or more stereocenters can exist as enantiomeric pairs consisting of opposite configurations at a stereogenic center, commonly labeled R and S. When a molecule contains multiple stereocenters, the two enantiomers are mirror images of each other, while the remaining stereoisomers that are not mirror images are diastereomers.

Optical activity is a defining feature of enantiomers: each enantiomer rotates plane-polarized light in opposite directions, with equal magnitude in a purely racemic, pure environment. The observed rotation depends on concentration, solvent, temperature, and the wavelength of light, so the sign alone does not fully determine identity.

Relevance and applications: Enantiomers can exhibit markedly different biological activities because living systems are chiral. In pharmaceuticals, agrochemicals, and flavors, enantiomeric purity is often important; racemic mixtures may contain both active and inactive or harmful enantiomers. Common approaches to obtain or analyze enantiomeric purity include chiral resolution, formation of diastereomeric salts, asymmetric synthesis using chiral catalysts, and chiral chromatography.

Terminology and measurement: concepts such as enantiomeric excess, enantiomeric ratio, and enantiomeric purity quantify the imbalance between enantiomers. Techniques include polarimetry and various forms of chiral chromatography.