stéréoisomers

Stereoisomers are a type of isomer, which are molecules with the same molecular formula but different arrangements of atoms in space. Unlike constitutional isomers, stereoisomers have the same connectivity between atoms, but their three-dimensional structures differ. This difference in spatial arrangement can lead to distinct physical and chemical properties.

There are two main categories of stereoisomers: enantiomers and diastereomers. Enantiomers are stereoisomers that are non-superimposable mirror images of each other, much like a left and right hand. Molecules that are enantiomers are said to be chiral. Diastereomers, on the other hand, are stereoisomers that are not mirror images of each other. This can occur when a molecule has multiple chiral centers, and the configurations at some, but not all, of these centers are inverted.

The concept of stereoisomerism is particularly important in organic chemistry and biochemistry. The biological activity of molecules, such as drugs and enzymes, is often highly dependent on their specific three-dimensional structure. For instance, one enantiomer of a drug might be therapeutically effective, while the other could be inactive or even harmful. Therefore, understanding and controlling stereoisomerism is crucial in fields like pharmaceutical development and synthesis. Geometric isomerism, such as cis-trans isomerism in alkenes, is another important type of stereoisomerism that arises from restricted rotation around a double bond or in a ring structure.