What are diastereomers and how do they differ from enantiomers?

Diastereomers are stereoisomers that are not mirror images of each other, unlike enantiomers which are mirror images.

In more detail, diastereomers and enantiomers are both types of stereoisomers, which are molecules that have the same molecular formula and sequence of bonded atoms, but differ in the three-dimensional orientations of their atoms in space. This difference in spatial arrangement arises due to the presence of chiral centres or double bonds in the molecule.

Diastereomers are stereoisomers that are not mirror images of each other. They occur when two or more stereoisomers of a compound have different configurations at one or more (but not all) of the equivalent (related) stereocenters and are not mirror images of each other. For example, in molecules with two chiral centres, there are four possible stereoisomers. Two of these are mirror images, known as enantiomers, and the other two are diastereomers. Diastereomers can have different physical properties, such as boiling point, melting point, and solubility, and they can also exhibit different chemical reactivity.

On the other hand, enantiomers are a type of stereoisomer where the molecules are mirror images of each other, much like left and right hands. They occur when all the stereocenters in a molecule have the opposite configuration. Enantiomers have identical physical properties except for the direction in which they rotate polarised light and how they interact with different optical isomers. This property is called optical activity.

In summary, while both diastereomers and enantiomers are types of stereoisomers, they differ in their spatial arrangement and their physical and chemical properties. Diastereomers are not mirror images and can have different physical properties and chemical reactivity, while enantiomers are mirror images and differ mainly in their optical activity.