Diastereomers

Diastereomers

Diastereomers are a type of stereoisomer found in chemistry, specifically in the study of organic compounds. Unlike enantiomers, which are non-superimposable mirror images of each other, diastereomers are stereoisomers that are not mirror images. This distinction is crucial in understanding the behavior and properties of molecules in biological systems and in synthetic chemistry.

Definition

Diastereomers are defined as stereoisomers that have two or more chiral centers and are not related as mirror images. They have different physical properties and reactivity, which makes them particularly interesting in the field of chiral synthesis and pharmacology.

Characteristics

• Chirality: Diastereomers contain chiral centers, which are atoms bonded to four different substituents. The configuration of these chiral centers can vary, leading to different diastereomers.
• Physical Properties: Unlike enantiomers, diastereomers have different melting points, boiling points, solubilities, and other physical properties. This is because they do not share the same spatial arrangement of atoms.
• Chemical Properties: Diastereomers can exhibit different reactivity and selectivity in chemical reactions. This is particularly important in asymmetric synthesis where the goal is to selectively produce one diastereomer over another.

Examples

A classic example of diastereomers is the pair of tartaric acid isomers: meso-tartaric acid and D,L-tartaric acid. While D-tartaric acid and L-tartaric acid are enantiomers, meso-tartaric acid is a diastereomer of both.

Importance in Chemistry

Diastereomers play a significant role in the development of pharmaceuticals. Many drugs are chiral, and the different diastereomers can have vastly different biological activities. For instance, one diastereomer might be therapeutically active, while another might be inactive or even harmful.

Separation Techniques

Diastereomers can often be separated by conventional means such as crystallization, distillation, or chromatography due to their differing physical properties. This is in contrast to enantiomers, which require chiral resolution techniques for separation.

Also see

• Enantiomers
• Chirality (chemistry)
• Stereochemistry
• Chiral resolution
• Asymmetric synthesis