24.1 Naming Amines

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.

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.

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.

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

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

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

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).

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.

Problem 24-1

Name the following compounds:

(a)

(b)

(c)

(d)

(e)

(f)

Problem 24-2

Draw structures corresponding to the following IUPAC names:

(a)

Triisopropylamine

(b)

Triallylamine

(c)

N-Methylaniline

(d)

N-Ethyl-N-methylcyclopentylamine

(e)

N-Isopropylcyclohexylamine

(f)

N-Ethylpyrrole

Problem 24-3

Draw structures for the following heterocyclic amines:

(a)

5-Methoxyindole

(b)

1,3-Dimethylpyrrole

(c)

4-(N,N-Dimethylamino)pyridine

(d)

5-aminopyrimidine