Stéréoisomère

Stéréoisomère are a type of isomerism in chemistry where molecules have the same molecular formula and the same atom connectivity, but differ in the three-dimensional arrangement of their atoms in space. This difference in spatial arrangement leads to distinct physical and chemical properties.

There are two main categories of stéréoisomers: enantiomers and diastereomers. Enantiomers are stéréoisomers that are non-superimposable mirror images of each other. They are often described as chiral, similar to how a left hand and a right hand are mirror images but cannot be perfectly overlaid. Enantiomers typically have identical physical properties such as melting point and boiling point, but can differ in their interaction with plane-polarized light (optical activity) and in their biological activity.

Diastereomers, on the other hand, are stéréoisomers that are not mirror images of each other. This occurs when a molecule has more than one chiral center or contains cis-trans isomerism in alkenes or rings. Unlike enantiomers, diastereomers can have different physical and chemical properties. For example, cis-trans isomers of alkenes will have different boiling points and solubilities. The term stéréoisomère encompasses both enantiomers and diastereomers, highlighting the importance of three-dimensional structure in determining molecular behavior.