Chirality

In-depth explanation of Chirality

A molecule is chiral if it is non-superimposable on its mirror image, which is the same as saying it lacks a plane of symmetry. Chirality most commonly arises from a stereocentre, usually a carbon atom bonded to four different groups. Chiral molecules exist as a pair of mirror-image forms called enantiomers, which have identical physical properties in an achiral environment. Chirality is vital in biology because enzymes and receptors are themselves chiral and typically recognize only one enantiomer of a substrate or drug.

Going deeper: Chirality

Key ideas: A carbon bonded to four different groups is a stereocentre, and a molecule not superimposable on its mirror image is chiral. Check for any plane or centre of symmetry: if present, the molecule is achiral. Allenes, biaryls and helices can be chiral without stereocentres. Chiral molecules rotate plane polarised light and react differently with other chiral molecules such as enzymes.

Common mistakes and connections: Students assume any molecule with a stereocentre is chiral, which fails for meso compounds. They also label a carbon as chiral when two of its groups look different but are the same. Links to enantiomers, optical activity and drugs, where thalidomide is a famous example.

Visualization of Chirality

Glycine is the one achiral amino acid because its alpha carbon carries two hydrogens; replacing one with a different group makes the carbon a chiral centre. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Lactic acid has one chiral centre, the carbon bearing the OH group, so it exists as two enantiomers.

Where Chirality fits in Organic Chemistry

Chirality is topic 19 of 148 in Organic Chemistry.

Related topics

• StereoisomerismIntermediate
• Cis-Trans IsomerismIntermediate
• E-Z NotationAdvanced
• EnantiomersIntermediate
• DiastereomersAdvanced
• Meso CompoundsAdvanced

Browse all 148 topics in Organic Chemistry