Diastereomers are a type of stereoisomer (compounds with the same molecular formula and connectivity but different spatial arrangements) that are not mirror images of each other.
Key points about diastereomers:
- They have the same molecular formula and same bonding sequence, but differ in the arrangement of atoms in space.
- Unlike enantiomers, which are non-superimposable mirror images, diastereomers are not related as mirror images.
- Diastereomers usually occur when a molecule has two or more chiral centers.
- Example: If a molecule has two chiral centers, it can form up to 2n2^n stereoisomers (where nn = number of chiral centers). Some pairs will be enantiomers, while others will be diastereomers.
- Physical and chemical properties: Diastereomers often have different melting points, boiling points, solubilities, and reactivities, unlike enantiomers, which usually share identical properties (except for optical activity).
Example: Tartaric acid has two chiral centers. Its stereoisomers include:
- A pair of enantiomers (mirror images).
- A third stereoisomer (the meso form), which is achiral.
The enantiomers and the meso form are diastereomers of each other.