Enantiomer
Definition and meaning of Enantiomer in chemistry.
Enantiomer refers to one of a pair of stereoisomers that are non-superimposable mirror images of each other, much like a person's left and right hands. Enantiomers arise when a molecule contains a chiral center, most commonly a carbon atom bonded to four different substituents.
In more detail
Because enantiomers differ only in the three-dimensional arrangement of their groups, they share identical melting points, boiling points, densities, and solubilities in achiral environments. They differ, however, in how they rotate plane-polarized light: one enantiomer rotates it clockwise (dextrorotatory, +) and the other rotates it by the same amount counterclockwise (levorotatory, −). This distinction matters enormously in biology and medicine, since enzymes and receptors are themselves chiral and often bind, metabolize, or respond to one enantiomer very differently than the other, sometimes with dramatically different biological effects.
Key facts
| Field | Organic Chemistry |
|---|---|
| Relationship | Non-superimposable mirror images |
| Requires | A chiral center (e.g., a carbon with four different groups) |
| Optical rotation | Equal magnitude, opposite direction (+ vs. −) |
Lactic acid (C3H6O3) exists as two enantiomers, (R)-lactic acid and (S)-lactic acid; (S)-lactic acid is the form produced during anaerobic muscle metabolism, while a mixture of both forms accumulates in fermented foods.
Frequently asked questions
Are enantiomers the same as diastereomers?
No. Enantiomers are non-superimposable mirror images of each other, while diastereomers are stereoisomers that are not mirror images and typically have different physical properties.
Can enantiomers be separated by ordinary distillation or crystallization?
Not directly, since they share identical physical properties; separating them (resolution) requires a chiral resolving agent, chiral chromatography, or enzymatic methods.