will explore momentarily. These differences enable one to separate these products by common
laboratory techniques such as crystallization, filtration, distillation, and others. Once separated,
these diastereomers can be reacted to regenerate the original enantiomers.
Diastereomers
Diastereomers are non-mirror-image configurational isomers. Diastereomers occur when a
molecule has two or more stereogenic centers and differs at some, but not all, of these centers. This
means that diastereomers are required to have multiple chiral centers. For any molecule with n
chiral centers, there are 2n possible stereoisomers. Thus, if a compound has two chiral carbon
atoms, it has a maximum of four possible stereoisomers, as shown in Figure 2.13.
Figure 2.13. 2 n Possible Stereoisomers (n = chiral centers)
Four stereoisomers with two chiral centers; enantiomers = I/II and III/IV pairs, and all other
combinations are diastereomers.In this image, one can see that I and II are mirror images of each other and are therefore
enantiomers of each other. Similarly, III and IV are enantiomers. However, I and III are not. These are
stereoisomers that are not mirror images and are thus diastereomers. Notice that other
combinations of non-mirror-image stereoisomers are also diastereomers: I and IV, II and III, and II
and IV.
Diastereomers have different chemical properties. However, they might behave similarly in
particular reactions because they have the same functional groups. Because they have different
arrangements in space, they will consistently have different physical properties. Diastereomers will