Amines are organic compounds derived from ammonia, NH3, by replacing one or more of its hydrogen atoms with alkyl or aryl groups. The nitrogen atom keeps its lone pair, and this lone pair is behind almost all amine chemistry.Amines are classified by how many carbon groups are bonded to the nitrogen:Primary: one group, e.g. ethylamine, CH3CH2NH2.
Secondary: two groups, e.g. dimethylamine, (CH3)2NH.
Tertiary: three groups, e.g. trimethylamine, (CH3)3N.When the nitrogen is bonded directly to a benzene ring the compound is an aromatic amine. The simplest is phenylamine, C6H5NH2.Short-chain amines such as methylamine and ethylamine are gases or volatile liquids with a fishy smell. They are very soluble in water because the N-H groups and the nitrogen lone pair form hydrogen bonds with water molecules. Solubility falls as the carbon chain gets longer.Primary and secondary amines can hydrogen bond with each other, so their boiling temperatures are higher than those of alkanes of similar Mr. They are lower than those of the corresponding alcohols, because nitrogen is less electronegative than oxygen and the hydrogen bonds between amine molecules are weaker. Tertiary amines have no N-H bond and cannot hydrogen bond with each other.The lone pair also lets amines act as bases and as nucleophiles, which the following lessons explore.
Secondary: two groups, e.g. dimethylamine, (CH3)2NH.
Tertiary: three groups, e.g. trimethylamine, (CH3)3N.When the nitrogen is bonded directly to a benzene ring the compound is an aromatic amine. The simplest is phenylamine, C6H5NH2.Short-chain amines such as methylamine and ethylamine are gases or volatile liquids with a fishy smell. They are very soluble in water because the N-H groups and the nitrogen lone pair form hydrogen bonds with water molecules. Solubility falls as the carbon chain gets longer.Primary and secondary amines can hydrogen bond with each other, so their boiling temperatures are higher than those of alkanes of similar Mr. They are lower than those of the corresponding alcohols, because nitrogen is less electronegative than oxygen and the hydrogen bonds between amine molecules are weaker. Tertiary amines have no N-H bond and cannot hydrogen bond with each other.The lone pair also lets amines act as bases and as nucleophiles, which the following lessons explore.