An asymmetric carbon atom (also called a chiral carbon) is a carbon atom that is attached to four different atoms or groups of atoms.
Because of these four different groups, the carbon becomes a center of chirality, meaning the molecule can exist in two non-superimposable mirror-image forms, called enantiomers.
Key Features of an Asymmetric Carbon Atom
- It must be sp³ hybridized (tetrahedral geometry).
- It must be bonded to four different substituents.
- The presence of an asymmetric carbon usually makes the compound optically active (it can rotate plane-polarized light).
- Molecules with asymmetric carbons often exist as pairs of enantiomers (R and S configurations).
Examples
- Lactic acid (CH₃–CH(OH)–COOH):
The middle carbon is attached to –H, –OH, –COOH, and –CH₃ → four different groups → asymmetric carbon. - Glucose: Contains multiple asymmetric carbons, giving rise to many stereoisomers.
In short:
An asymmetric carbon atom is a carbon bonded to four different groups, making the molecule chiral and capable of showing optical activity.