A stereogenic carbon, also called a chiral carbon, is a carbon atom bearing four different groups. It matters because such a carbon gives rise to stereoisomerism: swapping any two of its groups produces a non-superimposable mirror image, so the molecule and its mirror image are distinct enantiomers. A carbon with two or more identical groups is not stereogenic, since exchanging them leaves the molecule unchanged.

手性碳(又称立体中心碳)是连有四个不同基团的碳原子。它之所以重要,是因为这样的碳会产生立体异构:交换其上任意两个基团便得到一个不能重合的镜像,于是分子与其镜像成为两种不同的对映异构体。带有两个或更多相同基团的碳不是手性碳,因为交换这些相同基团后分子并无变化。