How do enantiomers differ from each other?

Enantiomers are mirror images of each other that cannot be superimposed.

Enantiomers are a type of stereoisomer, specifically they are chiral molecules that are non-superimposable mirror images of each other. This means that, despite having the same molecular formula and sequence of bonded atoms, they are arranged differently in space. This difference is due to the presence of a chiral centre, typically a carbon atom bonded to four different groups.

The concept of chirality is crucial in understanding enantiomers. A molecule is chiral if it cannot be superimposed onto its mirror image, much like your left and right hands. In chemistry, a chiral centre is usually a carbon atom bonded to four different groups. The different spatial arrangement around this chiral centre gives rise to enantiomers.

Enantiomers have identical physical properties in an achiral environment. They have the same boiling point, melting point, and solubility. However, they interact differently with plane-polarised light. One enantiomer will rotate the plane of polarisation in one direction (clockwise, known as dextrorotatory), while the other enantiomer will rotate it in the opposite direction (anti-clockwise, known as levorotatory). This property is known as optical activity and is a key way to distinguish between enantiomers.

In a biological context, enantiomers can have drastically different effects. This is because the chiral centres in biological molecules interact differently with each enantiomer. For example, one enantiomer of a drug may be beneficial, while the other may be harmful. This highlights the importance of being able to synthesise and identify specific enantiomers in pharmaceutical chemistry.

In summary, enantiomers are chiral molecules that are mirror images of each other but cannot be superimposed due to the presence of a chiral centre. They have identical physical properties in an achiral environment but exhibit optical activity. Their different interactions with biological molecules can lead to different effects, emphasising the importance of chirality in chemistry.