Amines are organic compounds which contain and are often actually based on one or more atoms of nitrogen. Structurally amines resemble ammonia in that the nitrogen can bond up to three hydrogens, but amines also have additional properties based on their carbon connectivity. In an amine, one or more of the hydrogen atoms from ammonia are replaced by organic substituents like alkyl (alkane chain) and aryl (aromatic ring) groups.

Another type of organic molecule contains nitrogen without being, strictly speaking, an amine: carboxylic acid derivatives containing a trivalent (three-bond) ammonia in ground state are actually amides instead of amines. Amides and amines have different structures and properties, so the distinction is actually very important. Organic-nitrogen compounds containing metals are also called amides, so if you see a molecule that has a nitrogen and either a carbonyl group or a metal next to that nitrogen, then you know that molecule should be an amide instead of an amine.

Amines can be either primary, secondary or tertiary, depending on the number of carbon-containing groups that are attached to them. If there is only one carbon-containing group (such as in the molecule CH₃NH₂) then that amine is considered primary. Two carbon-containing groups makes an amine secondary, and three groups makes it tertiary. Utilizing the lone electron pair of nitrogen, it is sometimes energetically favored to use the nitrogen as a nucleophile and thus bind a fourth carbon-containing group to the amine. In this case, it could be called a quaternary ammonium ion.

Primary Amine

Secondary Amine

Tertiary Amine

An organic compound with multiple amine groups is called a diamine, triamine, tetraamine and so forth, based on the number of amine groups (also called amino groups) attached to the molecule. The chemical formula for methylene diamine (also called diaminomethane), for example, would be as follows: H₂N-CH₂-NH₂