Enantioomers

Enantiomers are a pair of stereoisomers that are non-superimposable mirror images of each other. They arise in molecules that contain one or more chiral centers, typically carbon atoms bonded to four different substituents. This property is known as chirality, and the chiral centers are often referred to as asymmetric or stereogenic centers. Enantiomers exhibit identical physical properties such as melting point, boiling point, and density, but they differ in how they interact with plane-polarized light and in their biological activity.

The relationship between enantiomers is analogous to that between a right hand and a left hand; one cannot be rotated or manipulated to match the other. This non-superimposability is a defining characteristic of enantiomers. In a chiral molecule, the arrangement of atoms around the chiral center can exist in two distinct forms, often denoted as *R* (rectus) and *S* (sinister) using the Cahn-Ingold-Prelog priority rules. These labels indicate the spatial arrangement of substituents relative to each other, but they do not imply any inherent directionality or handedness.

Enantiomers have identical chemical and physical properties in an achiral environment, meaning they behave identically in the absence of chiral influences. However, in a chiral environment—such as biological systems—they may exhibit different behaviors. For example, one enantiomer of a drug may be therapeutically active, while the other may be inactive, toxic, or even harmful. This phenomenon is critical in pharmacology, where the biological activity of enantiomers can vary dramatically.

Enantiomers can be separated through techniques such as chiral chromatography or by reacting them with a chiral resolving agent to form diastereomers, which have distinct physical properties and can be separated using conventional methods. The study of enantiomers is fundamental in fields like organic chemistry, biochemistry, and pharmaceutical science, where stereochemistry plays a crucial role in determining molecular function and interaction.