Final answer:
Stereoisomers with two asymmetric centers that have the same configuration are called meso compounds; they have a plane of symmetry and are not optically active. Unlike diastereomers or enantiomers, meso compounds do not differ in spatial orientation between two stereoisomers in a way that creates mirror images.
Step-by-step explanation:
Stereoisomers with two asymmetric centers are called meso compounds if the configuration of both asymmetric centers in one stereoisomer is the same as the configuration of the asymmetric centers in the other stereoisomer. This type of stereoisomer has a plane of symmetry and thus is not optically active, even though the molecule has chiral centers.
For instance, cis-1,2-dimethylcyclopropane has two asymmetric carbon atoms. However, because of its plane of symmetry, it is a meso compound and does not have enantiomers. On the other hand, diastereomers like cis-but-2-ene and trans-but-2-ene have the same molecular formula and bond connectivity but differ in spatial orientation of atoms and lack a plane of symmetry. Diastereomers are not mirror images of each other, unlike enantiomers which are non-superimposable mirror images and have configurations that are opposite at every asymmetric carbon.