Carboxylic Acids and Derivatives - Structure of Amides (A-Level Chemistry)
Structure of Amides
Amides
The functional group for an amide is R-CONHā.
The structure of an amide is:
The C atom of the acyl group is attached to an amino group.
Amides can be classified as primary, secondayr or tertiary:
- Primary amides – In primary amides, there is just an -NHā group attached to the C atom.
- Secondary amides – In secondary amides, one of the hydrogen atoms on the N atom is replaced with an alkyl group
- Tertiary amides – In tertiary amides, both H atoms are replaced with alkyl groups
Naming Amides
- Amides are named with the alkyl prefix. This is the name of the carbon chain the amide group is attached to and will be followed by the amide suffix.
- The presence of either single or double C-C bonds changes the prefix. If there are single bonds between C atoms, the prefix is followed by -an and the suffix -amide. If there are double bonds between C atoms in the alkyl chain, the prefix is followed by -en and the suffix -amide.
- To name substituted amides, the prefix N- is used to name the alkyl groups attached to the N atom. If alkyl groups on the N atom are different, they are named in alphabetical order.
Some examples are given here:
Reactions of Amides
Hydrolysis
In the hydrolysis of amides, the C-N bond in the amide group is broken to produce an amine (or ammonia in the case of unsubstituted amides).
Hydrolysis of amides is brought about by refluxing a solution of the amide amide with either an acid such as hydrochloric acid or an alkali such as sodium hydroxide.
- Acidic hydrolysis – The products of the hydrolysis of an amide with an acid are a carboxylic acid and an amine (or ammonia for unsubstituted amides), which react with excess Hāŗ to form an ammonium salt.
- Alkaline hydrolysis – The products of the hydrolysis of an amide with an alkali are a carboxylate salt and an amine (or ammonia for unsubstituted amides)
Reduction
Amides can be reduced by of lithium tetrahydroaluminate (LiAlHā) to form an amine and water.
Amides as Bases
Amines act as bases by donating the lone pair of electrons on their N atom to Hāŗ ions in solution.
Amides can also act as bases in the same way. However, the presence of a partial positive charge on the C atom of the acyl group will attract the lone pair of electrons on the N atom of the amide group towards itself, so that it becomes less readily donated to Hāŗ. As a result amides are much weaker bases than amines.
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