amine

An amine is what you get when you take ammonia (NH3) and replace one, two, or three of its hydrogen atoms with carbon-containing groups. That gives the trio of fishy, often pungent compounds behind the smell of rotting fish, the sharpness of a spoiled meat market, and the basic chemistry inside countless drugs. The defining feature is a nitrogen atom carrying a lone pair of electrons that loves to grab protons and attack electron-poor carbons.

Amines are classified by how many carbon groups hang off nitrogen, not by the carbon they sit on. A primary (1°) amine has one carbon group and looks like R-NH2 (for example CH3-NH2, methylamine); a secondary (2°) amine has two, R2NH; a tertiary (3°) amine has three, R3N, with no N-H left at all. The nitrogen is roughly sp3 hybridized and pyramidal, like a slightly squashed tripod, with the lone pair sitting in the fourth corner where the missing leg would be. That lone pair is the whole story: it makes amines basic (it grabs H+) and nucleophilic (it attacks carbon).

Amines are everywhere in real chemistry and biology. Neurotransmitters like dopamine, serotonin, and adrenaline are amines; so are amphetamines, antihistamines, and a huge fraction of pharmaceutical molecules, because the basic nitrogen lets a drug form a soluble salt and bind to receptors. Be careful with the naming convention, though: 1°, 2°, and 3° for amines counts groups on nitrogen, whereas the same labels for alcohols and alkyl halides count groups on the carbon bearing the functional group, so the rules look identical but mean different things.