A functional group is a specific group of atoms within a molecule that is responsible for the molecule’s characteristic chemical reactions.
In organic chemistry, the carbon “backbone” (the chain or ring of carbon atoms) is often relatively unreactive, while the functional group is the reactive site. Molecules with the same functional group tend to have similar properties and undergo similar types of reactions.
For example:
- Hydroxyl group (-OH): found in alcohols; makes molecules polar and able to form hydrogen bonds.
- Carbonyl group (C=O): found in aldehydes and ketones; affects reactivity with nucleophiles.
- Carboxyl group (-COOH): found in carboxylic acids; makes molecules acidic.
- Amino group (-NH₂): found in amines; makes molecules basic.
In short:
A functional group is the “reactive identity tag” of an organic molecule.