Enantiomers are a specific type of stereoisomer that are mirror images of each other and cannot be superimposed. They possess chirality, a property of having non-superimposable mirror images due to the presence of one or more chiral centers. Enantiomers have identical physical properties except for their interaction with plane-polarized light. They are denoted as “R” (rectus) and “S” (sinister) enantiomers based on the Cahn-Ingold-Prelog system for assigning priorities to substituents around a chiral center.

Here are some key points about enantiomers:

1. Chirality: Enantiomers arise from chiral molecules that have at least one chiral center. Chiral centers are carbon atoms bonded to four different substituents.
2. Mirror Images: Enantiomers are mirror images of each other. They cannot be perfectly aligned or superimposed through rotation or translation.
3. Configuration: The arrangement of substituents around a chiral center determines the configuration of the enantiomer. The “R” and “S” system assigns priorities to these substituents.
4. Optical Activity: Enantiomers exhibit different optical activity—they rotate the plane of plane-polarized light in opposite directions. One enantiomer rotates light clockwise (dextrorotatory), while the other rotates it counterclockwise (levorotatory).
5. Naming: Enantiomers are often named with the prefix “(+)” or “(-)” to indicate their optical activity or using the descriptors “d” and “l” (though these are now generally replaced with “R” and “S”).
6. Properties: Enantiomers have identical physical properties (melting point, boiling point, etc.) except for their interactions with chiral environments (like polarized light or other chiral molecules).
7. Chiral Plane: Enantiomers lack a plane of symmetry. If a molecule has an internal plane of symmetry, it is achiral.
8. Biological Significance: Many biomolecules are chiral, and their interactions with other biomolecules or enzymes can be enantioselective—meaning one enantiomer is preferred over the other.
9. Drug Development: The effects of enantiomers can differ significantly. One enantiomer of a drug may have a desired therapeutic effect, while the other may cause unwanted side effects.
10. Racemic Mixture: A racemic mixture contains equal amounts of both enantiomers and is optically inactive due to the cancellation of their optical rotations.

Understanding enantiomers is crucial in various scientific disciplines, including chemistry, biology, medicine, and pharmacology. Enantiomerism has important implications for drug design, understanding biological processes, and explaining the properties and behavior of chiral molecules.