Any of a class of nitrogen-containing organic compounds derived, either in principle or in practice, from ammonia (NH). Almost all their chemical names end in -ine. Replacement of one, two, or all three of the hydrogen atoms in ammonia with organic groups yields primary, secondary, or tertiary amines, respectively. Addition of a fourth hydrogen with an accompanying positive charge on the nitrogen atom results in a quaternary amine. Naturally occurring amines include alkaloids, present in certain plants; some neurotransmitters, including dopamine and epinephrine; and histamine. Industrially important amines include aniline, ethanolamine, and others, used in making rubber, dyes, pharmaceuticals, and synthetic resins and fibres and in a host of other applications. A nitrogen atom with one or two hydrogens is often referred to as an amino group.