Amines

1. Introduction

Amines are organic derivatives of ammonia ($\ce{NH3}$) in which one, two or three hydrogen atoms are replaced by alkyl or aryl groups. They contain the basic nitrogen and are responsible for the basicity of many natural products (alkaloids, amino acids).

Classification (by number of carbon groups on nitrogen):

• Primary (1 degree): one carbon on N, $\ce{R-NH2}$, e.g. methylamine $\ce{CH3NH2}$.
• Secondary (2 degree): two carbons on N, $\ce{R2NH}$, e.g. dimethylamine $\ce{(CH3)2NH}$.
• Tertiary (3 degree): three carbons on N, $\ce{R3N}$, e.g. trimethylamine $\ce{(CH3)3N}$.
• Quaternary ammonium salt: four carbons on N, $\ce{R4N+X-}$.

(Note: 1 degree/2 degree/3 degree for amines counts groups on nitrogen, unlike alcohols/haloalkanes which count groups on the carbon bearing the functional group.)

The nitrogen is $sp^3$ hybridized and pyramidal, carrying a lone pair that makes amines basic and nucleophilic.

2. Nomenclature and Isomerism

Common names: name the alkyl group(s) and add -amine (methylamine, ethylmethylamine). IUPAC: alkanamine (methanamine $\ce{CH3NH2}$, ethanamine $\ce{CH3CH2NH2}$).

Amines show chain, position, functional (with nitro compounds) and metamerism ($\ce{C3H9N}$: propylamine, ethylmethylamine, trimethylamine).