19.3 : Nomenclature of Secondary and Tertiary Amines

The secondary and tertiary amines are derivatives of ammonia, where two and three of its hydrogens are replaced by alkyl groups, respectively. Secondary and tertiary amines can be symmetrical with identical alkyl groups attached to the nitrogen atom or unsymmetrical when more than one type of alkyl group is present. The standard nomenclature of secondary and tertiary amines is similar to the names given to the primary amines. They are generally named alkylamines. As depicted in Figure 1, for symmetrical secondary and tertiary amines, prefixes di- and tri- are used, respectively. On the other hand, in the case of unsymmetrical amines, individual substituents are identified and listed alphabetically.

Figure 1. The nomenclature of symmetric and asymmetric secondary and tertiary amines.

In the IUPAC nomenclature, the secondary and tertiary amines are named N-alkylalkanamines. The IUPAC name for a structure is assigned via the following protocol:

1. First, identify the alkyl groups attached to the nitrogen atom.
2. Next, select the longest chain as the parent, while other alkyl groups are listed as substituents. While numbering the parent hydrocarbon chain, assign the lowest number to the carbon atom bearing nitrogen atom.
3. Then, assign locants to each substituent. Use the letter N as the locant for the alkyl groups attached to the nitrogen atom.
4. Finally, specify the configuration of the chiral center at the beginning of the name, if any is present.

Two examples of the above are illustrated in Figure 2.

Figure 2. The IUPAC names of two example amines.

IUPAC names for quaternary ammonium ions are assigned by naming them as secondary and tertiary amines. However, the suffix -amine is replaced with -ammonium, followed by the name of counterion, as depicted in Figure 3.

Figure 3. The IUPAC names of various quaternary amines.