diastéréomères

Diastereomers are a type of stereoisomer that are not mirror images of each other. Stereoisomers are molecules that have the same chemical formula and connectivity but differ in the three-dimensional arrangement of their atoms. In contrast to enantiomers, which are non-superimposable mirror images, diastereomers are stereoisomers that are not enantiomers. This means that if you have two stereoisomers, and they are not mirror images of each other, they must be diastereomers.

The presence of multiple stereocenters in a molecule often leads to the existence of diastereomers. For a molecule with n stereocenters, there can be a maximum of 2^n stereoisomers. If all these stereoisomers are considered in pairs, and a pair consists of stereoisomers that are not mirror images, then they are diastereomers. For example, a molecule with two stereocenters can have up to four stereoisomers. These can be arranged into two pairs of enantiomers, or into multiple pairs of diastereomers.

A key difference between enantiomers and diastereomers is their physical and chemical properties. Enantiomers have identical physical properties such as melting point, boiling point, and solubility, except when interacting with other chiral substances or plane-polarized light. Diastereomers, on the other hand, typically have different physical properties. This difference arises because their three-dimensional structures are different, leading to different intermolecular forces and interactions. Their chemical reactivity can also differ, particularly in reactions involving other chiral molecules or in chiral environments. For instance, in biological systems, enzymes, which are chiral, can distinguish between diastereomers, leading to different biological activities.