diastereoméry

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 molecules that are diastereomers, you cannot place one directly on top of the other and have all the atoms align perfectly, nor are they mirror images.

Diastereomers can arise in molecules with multiple chiral centers or in cyclic compounds. For a molecule with two chiral centers, there are potentially four stereoisomers. Two of these will be enantiomers (a pair of mirror images), and the other two will also be enantiomers. However, the relationship between a stereoisomer from one enantiomeric pair and a stereoisomer from the other enantiomeric pair is diastereomeric. For example, if a molecule has chiral centers A and B, a specific configuration at A and a specific configuration at B will form one stereoisomer. Its enantiomer will have the opposite configuration at both A and B. A diastereomer would have the same configuration at A but the opposite at B, or vice versa.

A key characteristic of diastereomers is that they often have different physical and chemical properties. Unlike enantiomers, which typically have identical physical properties (melting point, boiling point, solubility) except for their interaction with plane-polarized light and their reactivity with other chiral molecules, diastereomers can differ in melting point, boiling point, solubility, density, and reactivity with achiral reagents. This difference in properties makes the separation of diastereomers easier than the separation of enantiomers, often achievable through standard laboratory techniques like chromatography or fractional crystallization.