diastereomericity

Diastereomericity refers to a specific type of stereoisomerism where stereoisomers are not mirror images of each other. Stereoisomers are molecules that have the same molecular formula and the same connectivity of atoms but differ in their three-dimensional arrangement. When stereoisomers are not mirror images, they are classified as diastereomers.

This relationship arises in molecules with more than one stereocenter, which are typically chiral carbon atoms bonded to four different groups. If a molecule has two or more stereocenters, it can have multiple stereoisomers. Pairs of these stereoisomers that are not enantiomers (non-superimposable mirror images) are diastereomers. For example, a molecule with two chiral centers can potentially exist as four stereoisomers, forming two pairs of enantiomers. Each stereoisomer in one enantiomeric pair will be a diastereomer to each stereoisomer in the other enantiomeric pair.

Unlike enantiomers, diastereomers have different physical properties such as melting point, boiling point, solubility, and refractive index. This difference in properties is significant in chemistry, as it allows for their separation by standard laboratory techniques like chromatography or fractional crystallization. Diastereomers also exhibit different chemical reactivity, especially in reactions involving stereospecific or stereoselective steps. The presence of diastereomericity is a key concept in understanding the stereochemical outcomes of many organic reactions and in the design and synthesis of complex molecules, including pharmaceuticals.