Enantiomerism is a type of stereoisomerism where two molecules are non-superimposable mirror images of each other. Enantiomers are chiral molecules, meaning they lack an internal plane of symmetry and cannot be aligned perfectly through rotation or translation. Enantiomerism arises due to the presence of chiral centers, which are asymmetric carbon atoms in a molecule bonded to four different substituents.

Enantiomers have the same physical properties (such as melting point and boiling point) but exhibit different interactions with polarized light. This property is known as optical activity. Enantiomers rotate the plane of polarized light in opposite directions—one rotates clockwise (dextrorotatory) and the other counterclockwise (levorotatory).

Key points about enantiomerism:

1. Chiral Molecules: Enantiomers are molecules that possess chiral centers. A molecule with n chiral centers can have 2^n possible stereoisomers (though not all of these may be enantiomers).
2. Mirror Images: Enantiomers are mirror images of each other. They have the same connectivity of atoms but differ in spatial arrangement.
3. Configurations: Enantiomers have opposite configurations at every chiral center. One enantiomer may have a particular substituent in the R (right-hand) configuration, while the corresponding substituent in the other enantiomer is in the S (left-hand) configuration.
4. Optical Activity: Enantiomers rotate plane-polarized light in opposite directions and exhibit equal and opposite specific rotation values.
5. Naming: Enantiomers are often named using the R/S system (Cahn-Ingold-Prelog system) to describe the configuration at each chiral center.
6. Properties: Enantiomers have the same chemical and physical properties (except for their interaction with polarized light), but their interactions with other chiral molecules (e.g., enzymes, receptors) can be significantly different.
7. Biological Importance: Enantiomerism is crucial in the field of pharmacology and medicine. Different enantiomers of a drug can have distinct effects on the body, and regulatory agencies often require testing and approval for individual enantiomers.
8. Racemates: A racemic mixture is an equimolar mixture of enantiomers. Racemates do not exhibit optical activity because the optical rotations of the two enantiomers cancel each other out.
9. Chirality and Asymmetry: The presence of chirality (lack of superimposability) and asymmetry (presence of chiral centers) are essential for enantiomerism.

Understanding enantiomerism is crucial for fields like chemistry, pharmacology, and biology. It has implications in drug development, synthesis, and the interactions between biomolecules.