7.1: Amines - Structures and Names

 Learning Objectives

• Identify the general structure for an amine.
• Identify the functional group for amines.
• Determine the structural feature that classifies amines as primary, secondary, or tertiary.
• Use nomenclature systems to name amines.

Amines are classified according to the number of carbon atoms bonded directly to the nitrogen atom. A primary (1°) amine has one alkyl (or aryl) group on the nitrogen atom, a secondary (2°) amine has two, and a tertiary (3°) amine has three (Figure \(\PageIndex{1}\)).

Figure \(\PageIndex{1}\): The Structure of Amines Compared to Water, an Alcohol, and an Ether

To classify alcohols, we look at the number of carbon atoms bonded to the carbon atom bearing the OH group, not the oxygen atom itself. Thus, although 2-propanamine looks similar to 2-propanol, the former is a primary amine, while the latter is a secondary alcohol.

 

Example \(\PageIndex{1}\)

Name and classify each compound.

1. CH₃CH₂CH₂NH₂
2. 
3. CH₃CH₂NHCH₂CH₃
4. CH₃CH₂CH₂NHCH₃

Solution

1. There is only one alkyl group attached to the nitrogen atom, so the amine is primary. A group of three carbon atoms (a propyl group) is attached to the NH₂ group through an end carbon atom, so the name is 1-propanamine.
2. There are two methyl groups and one ethyl group on the nitrogen atom. The compound is N,N-dimethylethanamine, a tertiary amine.
3. There are two ethyl groups attached to the nitrogen atom; the amine is secondary, so the compound is N-ethylethanamine.
4. The nitrogen atom has a methyl group and a propyl group, so the compound is N-methyl-1-propanamine, a secondary amine.

Exercise \(\PageIndex{1}\)

Name and classify each compound.

1. 
2. 
3. CH₃CH₂CH₂CH₂NH₂
4. CH₃CH₂CH₂NHCH₂CH₂ CH₃

Example \(\PageIndex{2}\)

Draw the structure for each compound and classify.

1. N,N-dimethyl-2-propanamine
2. N-propyl-1-propanamine

Solution

1. The name indicates that there are an isopropyl group (in red) and two methyl groups (in green) attached to the nitrogen atom; the amine is tertiary.

   

2. The name indicates that there are two propyl groups attached to the nitrogen atom; the amine is secondary. (The third bond on the nitrogen atom goes to a hydrogen atom.) CH₃CH₂CH₂NHCH₂CH₂CH₃

Summary

An amine is a derivative of ammonia in which one, two, or all three hydrogen atoms are replaced by hydrocarbon groups. The amine functional group is as follows:

Amines are classified as primary, secondary, or tertiary by the number of hydrocarbon groups attached to the nitrogen atom. Amines are named by naming the alkyl groups attached to the nitrogen atom, followed by the suffix -amine.