Amine Functional Group | ChemTalk
The amine functional group is a nitrogen with a lone pair and three bonds. Learn about properties of amines, amine reactions, and amine group classification below.
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What is the amine functional group?
An amine is an organic functional group that has a basic nitrogen with a lone pair on it. The lone pair on the nitrogen makes it a basic nitrogen. An amine is derived from ammonia, which is a nitrogen with a lone pair and three hydrogen. Amines can be further classified by how many organic groups are present instead of hydrogen. This classification is discussed further below. The group is also a polar functional group.
If the amine is connected to a carbonyl group, it may also be referred to as an amide.
Structure of Amine Group
The amine structure is a nitrogen with a lone pair and three bonds to the nitrogen. The shape is pyramidal and has a sp3 hybridization. Amines are basic due to their lone pair
Types and Classification of Amines
Primary Amine: In a primary amine, one hydrogen is replaced by a different organic group and two hydrogens are bonded to the nitrogen. This molecule is also referred to an an amino group.
Primary Amine
Secondary Amine: A secondary amine has two hydrogens replaced by a different group and one hydrogen remains.
Tertiary Amine: Tertiary amines have all hydrogens replace by other organic groups.
Tertiary Amine
Cyclic Amine: A cyclic amine is a nitrogen with a lone pair that is in an aromatic ring
Ammonia is a special case in the case of amines. Ammonia has all three groups coming off they nitrogen as hydrogens.
Naming Amines
There are several different naming conventions for amines.
The main convention, which is IUPAC, is to list the amine as ‘amine’ with the position it is at. For example, below is a butane chain (four carbons) that has an amine at the second position. Therefore it is referred to as 2-aminobutane.
2-aminobutane
In some other naming conventions, the term ‘amine’ is put at the end. For example, the above molecule would be butanamine.
In aromatic or cyclic amines they often have common names. For example, below is aniline.
Aniline
Physical Properties of Amine Functional Groups
Often times amines will smell fishy. Most primary and secondary amines will be a gas at standard conditions.
Hydrogen bonding does occur in amines. The hydrogen from one amine interacts with the lone pair from another amine. This primarily occurs with primary and secondary amines.
The amine is also a polar functional group that is basic. Methylamine and dimethylamine both have a pka of about 10.6. Cyclic amines tend to increase in acidity due to the lone pair on the nitrogen delocalizing in to the ring.
Amines are typically nucleophiles in organic reactions.
In infrared spectroscopy, primary amines will display differently than secondary amines. NMR Spectroscopy can also identify amines. In 1H NMR the amine peak often shows up around 0.5-5ppm. If D2O is added to the system, the hydrogens attached to the nitrogen swap out, causing the signal to disappear.
When amines combust, they produce toxic nitrogen oxide gases. Methylamine is very flammable. Most other amines are less flammable, but will burn.
What Are Amines Used For?
Amines have many uses. Many medicines contain amine groups. In fact, it is estimate about 40% of all drugs contain an amine group. One example, morphine contains a tertiary amine group.
Nylon also contains amine groups. One of the monomers for nylon contains two amine functional groups. Nylon is a critical polymer used in many clothing items and industrial parts.
Other uses for amines include dyes, cosmetics, detergents, epoxies, and polymer formation.
Named Reactions Using Amines
To form an amine, many different synthetic routes have been discovered. For example, the Birch Reduction, Leuckart reaction, or the Hofmann Elimination. Additionally, they can be prepared through alkylation from an alcohol or from alkenes.
Amines are used in many reactions as well as reactant. For example, the Cope Reaction, Zincke Reaction, or the Emde Degradation.
