How do the nitrogen-containing families, amines and amides, differ in structure and behaviour?
Describe the structure, properties and formation of amines and amides, including the amide (peptide) linkage
A focused answer to the WACE Year 12 Chemistry dot point on amines and amides, comparing the amine functional group as a weak base with the amide linkage formed from a carboxylic acid and an amine, and the link to proteins, with a worked example and common exam mistakes.
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What this dot point is asking
The nitrogen-containing organic families are the amines and the amides. Both contain nitrogen, but their chemistry is quite different because of where the nitrogen sits.
Amines
An amine has a nitrogen atom bonded to one or more carbon chains, with the simplest being the -NH2 group attached to a carbon (a primary amine, such as ethylamine). The defining feature is the lone pair of electrons on the nitrogen.
Because the nitrogen lone pair can accept a proton, amines are weak bases:
They react with acids to form salts. Small amines hydrogen bond and so are soluble in water and have a characteristic fishy smell.
Amides and the amide linkage
An amide contains the -CONH2 group: a carbonyl (C=O) bonded directly to a nitrogen. It is formed by reacting a carboxylic acid with an amine (or ammonia), eliminating water:
Unlike amines, amides are not basic, because the nitrogen lone pair is delocalised into the adjacent carbonyl group and is therefore not available to accept a proton. This delocalisation also makes the amide linkage strong and rigid.
Link to proteins and polymers
When amino acids (which contain both -COOH and -NH2) join through amide linkages, the bond is called a peptide bond, and the polymer is a protein. The same linkage forms condensation polymers such as nylon and polyamides, which connects this dot point to the polymers topic.
Why this matters
Amines and amides are central to biochemistry (amino acids, proteins, DNA bases) and to materials science (polyamides such as nylon). The amide linkage is one of the two great condensation linkages, and the acid-base contrast between amines and carboxylic acids underpins how amino acids and buffers behave.