A chiral carbon atom is a carbon that has four different atoms or group of atoms bonded to it.

Chiral molecules are molecules that contain at least one chiral carbon.

If a carbon is not chiral, it is called achiral.

 

Stereoisomers

When a molecule is chiral, the mirror image of that molecule is a different molecule. The chiral molecule and its mirror image are stereoisomers of one another. More specifically, they are enantiomers of one another.

Enantiomers are nonsuperimposable mirror images.

D & L Notation for Monosaccharides

If the hydroxyl (OH) group on the last chiral carbon is on the right side, the sugar is the D enantiomer.

If the hydroxyl (OH) group on the last chiral carbon is on the left side, the sugar is the L enantiomer.

Note: Be sure to use the uppercase D & L; the lowercase d and l refers to something different.