Why can some sulfoxides exist as optically active forms?

Some sulfoxides can exist as optically active forms because the sulfoxide group is nonplanar. Unlike the planar structure of a carbonyl group, the sulfur atom in a sulfoxide is bonded to two different organic groups and possesses a lone pair of electrons, resulting in a trigonal pyramidal geometry.1

Because of this nonplanar, stable configuration, sulfoxides of the type R(S=O)R′, where the two organic groups (R and R′) are different, are chiral. This chirality allows them to be isolated in optically active forms. This property is similar to that of phosphines and is distinct from [amines], which generally do not maintain a stable configuration for optical activity due to rapid inversion.1