John McMurry, Professor Emeritus

24.1 • Naming Amines

Amines can be either alkyl-substituted (alkylamines) or aryl-substituted (arylamines). Although much of the chemistry of the two classes is similar, there are also substantial differences. Amines are classified as primary (RNH₂), secondary (R₂NH), or tertiary (R₃N), depending on the number of organic substituents attached to nitrogen. Thus, methylamine (CH₃NH₂) is a primary amine, dimethylamine [(CH₃)₂NH] is a secondary amine, and trimethylamine [(CH₃)₃N] is a tertiary amine. Note that this usage of the terms primary, secondary, and tertiary differs from our previous usage. When we speak of a tertiary alcohol or alkyl halide, we refer to the degree of substitution at the alkyl carbon atom, but when we speak of a tertiary amine, we refer to the degree of substitution at the nitrogen atom.

Three structures show tertiary-butyl alcohol (a tertiary alcohol), trimethylamine (a tertiary amine) and tertiary butyl amine (a primary amine).

Compounds containing a nitrogen atom with four attached groups also exist, but the nitrogen atom must carry a formal positive charge. Such compounds are called quaternary ammonium salts.

The structure of a quaternary ammonium salt, which is a nitrogen positive linked to four R groups and an X negative ion.

Primary amines are named in the IUPAC system in several ways. For simple amines, the suffix -amine is added to the name of the alkyl substituent. You might also recall from the chapter on Benzene and Aromaticity that the aromatic phenylamine, H₂N–C₆H₅, has the common name aniline.

The structures of tertiary-butyl amine, cyclohexylamine, and aniline. Aniline is enclosed in square parentheses.

Alternatively, the suffix -amine can be used in place of the final -e in the name of the parent compound.

The structures of 4,4-dimethylcyclohexanamine and 1,4-butanediamine. 4,4-dimethylcyclohexanamine has cyclohexane ring with two methyl groups on C4 and amine on C1. 1,4-butanediamine is four-carbon chain with amines on C1 and C4.

Amines with more than one functional group are named by considering the −NH₂ as an amino substituent on the parent molecule.

The structures of 2-aminobutanoic acid, 2,4-diaminobenzoic acid and 4-amino-2-butanone. The carbon atoms of 2-aminobutanoic acid and 4-amino-2-butanone are numbered explicitly.

Symmetrical secondary and tertiary amines are named by adding the prefix di- or tri- to the alkyl group.

The structures of diphenylamine and triethylamine. Diphenylamine has two benzene rings linked to an N H group. Triethylamine has a nitrogen atom linked to three ethyl groups.

Unsymmetrically substituted secondary and tertiary amines are referred to as N-substituted primary amines. The largest alkyl group takes the parent name, and the other alkyl groups are considered N-substituents on the parent (N because they’re attached to nitrogen).

N,N-dimethylpropylamine has a nitrogen linked to two methyl and a propyl group. N-ethyl-N-methylcyclohexylamine has cyclohexane linked to a nitrogen. This is connected to methyl and ethyl group.

Heterocyclic amines—compounds in which the nitrogen atom occurs as part of a ring—are also common, and each different heterocyclic ring system has its own parent name. The heterocyclic nitrogen atom is always numbered as position 1.