What makes a molecule chiral? It turns out that in the majority of cases chiral molecules result from carbon atoms that are bonded to four different groups. For example* C 2 in 2-butanol is attached to the four distinct groups -H* -Me* -Et* and -OH. There are two different ways to arrange four groups about tetrahedr al carbon* giving rise to chirality. (In fact* chiral molecules gave chemists evidence that carbon is indeed tetrahedral.) Such a carbon atom is called an asymmetric carbon because it lacks a plane of symmetry. Asymmetric carbons are also called "chiral carbons". Because asymmetric carbons give rise to stereoisomerism* they are stereogenic centers or stereocenters. Technica lly* there are other structural motifs that are stereocenters beside asymmetric carbons* but in practice the term "stereocenter" is used in place of "asymmetric carbon" to denote a carbon bonded to four different substituents.
Figure %: General description of asymmetric carbon atoms that are bonded to four different groups.