A functional group is a specific group of atoms within a molecule that determines the molecule’s characteristic chemical reactions and properties, regardless of the rest of the molecule’s structure.
For example:
- –OH (hydroxyl group): Found in alcohols, makes molecules polar and able to form hydrogen bonds.
- –COOH (carboxyl group): Found in carboxylic acids, makes molecules acidic.
- –NH₂ (amino group): Found in amines and amino acids, acts as a base.
- C=O (carbonyl group): Found in aldehydes and ketones, affects reactivity and polarity.
Think of the functional group as the “reactive center” of an organic compound — it largely controls how the molecule behaves in chemical reactions.