Amines classified by the number of groups on nitrogen: 1° amine (RNH2) — one alkyl/aryl group. 2° amine (R2NH) — two groups. 3° amine (R3N) — three groups. Quaternary ammonium salt (R4N+X-) — four groups, positively charged. Critical distinction: amine classification is based on nitrogen substitution, NOT carbon type. Methylamine (CH3NH2) is 1° even though the carbon is technically "primary" — the naming refers only to N. Aniline (C6H5NH2) is a primary aromatic amine. N-Methylaniline (C6H5NHCH3) is secondary. N,N-Dimethylaniline (C6H5N(CH3)2) is tertiary.