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WAChemistrySyllabus dot point

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.

Generated by Claude Opus 4.88 min answerUpdated 2026-06-02

Reviewed by: AI editorial process; not yet individually human-reviewed

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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:

\text{CH}_3\text{NH}_2 + \text{H}_2\text{O} \rightleftharpoons \text{CH}_3\text{NH}_3^+ + \text{OH}^-

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:

\text{R-COOH} + \text{H}_2\text{N-R}' \rightarrow \text{R-CONH-R}' + \text{H}_2\text{O}

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.

Amino acids and zwitterions

Because an amino acid carries both an acidic carboxyl group and a basic amine group, it can transfer a proton internally: the $\text{-COOH}$ donates its proton to the $\text{-NH}_2$ , giving a zwitterion with both a $\text{-COO}^-$ and a $\text{-NH}_3^+$ in the same molecule. The molecule is overall neutral but carries separated charges, which is why solid amino acids have high melting points and dissolve well in water (they behave like ionic species). In acidic solution the carboxylate picks up a proton and the molecule becomes a cation; in basic solution the ammonium loses a proton and it becomes an anion. The pH at which the zwitterion form dominates is the isoelectric point, a useful link to the acid-base topic of Unit 3.

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.

Exam-style practice questions

Practice questions written in the style of SCSA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

WACE 20226 marksThe amino acid alanine has the structure

\text{CH}_3\text{CH(NH}_2)\text{COOH}

. (a) Identify the two functional groups and state the acid-base role of each. (b) Draw the zwitterion and explain why it forms. (c) Write the equation for the condensation of two alanine molecules and name the linkage formed.

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A 6 mark question rewards the functional groups, the zwitterion explanation, and the condensation equation.

(a) The amine group $\text{-NH}_2$ is a base (its nitrogen lone pair accepts a proton); the carboxyl group $\text{-COOH}$ is an acid (it donates a proton).

(b) The zwitterion is $\text{CH}_3\text{CH(NH}_3^+)\text{COO}^-$ , with a positive $\text{-NH}_3^+$ and a negative $\text{-COO}^-$ . It forms because the carboxyl group transfers its proton to the more basic amine group within the same molecule, so the species is overall neutral but carries both charges.

(c) $2\,\text{CH}_3\text{CH(NH}_2)\text{COOH} \rightarrow \text{CH}_3\text{CH(NH}_2)\text{CO-NH-CH(CH}_3)\text{COOH} + \text{H}_2\text{O}$ . The new $\text{-CO-NH-}$ bond is an amide linkage, specifically a peptide bond.

Markers reward the amine-base/carboxyl-acid roles, the correctly charged zwitterion with reasoning, and the condensation equation losing water to form a peptide bond.

WACE 20205 marksCompare an amine and an amide that contain the same number of carbon atoms in terms of (i) acid-base behaviour and (ii) the availability of the nitrogen lone pair. Explain why this difference exists.

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A 5 mark compare answer needs the behaviour contrast and the structural reason.

(i) The amine is a weak base: its nitrogen lone pair accepts a proton, for example $\text{CH}_3\text{NH}_2 + \text{H}_2\text{O} \rightleftharpoons \text{CH}_3\text{NH}_3^+ + \text{OH}^-$ . The amide is essentially not basic and does not accept protons appreciably.

(ii) In the amine the nitrogen lone pair is localised on the nitrogen and freely available. In the amide the nitrogen is bonded directly to a carbonyl carbon, and the lone pair is delocalised into the adjacent C=O group.

Reason. Because the amide lone pair is delocalised into the carbonyl, it is no longer available to bond a proton, so the amide lacks the basicity of the amine. This delocalisation also gives the amide linkage extra strength and rigidity.

Markers reward the basic-versus-not-basic contrast, the free-versus-delocalised lone pair, and the carbonyl delocalisation explanation.