Amines and amides: WACE Year 12 Chemistry

Syllabus dot point

“Describe the structure, properties and formation of amines and amides, including the amide (peptide) linkage”

8 min readUpdated 2 Jun 2026

Quick answer

Amines contain the -NH2 group (or its substituted forms) and behave as weak bases because the nitrogen lone pair accepts a proton. Amides contain the -CONH2 linkage, formed by reacting a carboxylic acid with an amine (the amide or peptide bond). Amides are not basic like amines because the nitrogen lone pair is delocalised into the carbonyl.

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.

Amine

An organic compound containing a nitrogen atom bonded to carbon and hydrogen, derived from ammonia by replacing one or more hydrogen atoms with an alkyl group. The nitrogen lone pair makes amines weak bases.

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.

Amines are bases, carboxylic acids are acids

The amine -NH2 group is a base (proton acceptor) while the carboxylic acid -COOH group is an acid (proton donor). A molecule containing both, such as an amino acid, can act as both, which is why amino acids form zwitterions.

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}

Amide (peptide) linkage

The -CO-NH- bond formed when the carboxyl group of one molecule joins the amino group of another, releasing water. When this links amino acids it is called a peptide bond.

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.

Predicting amine basicity

Question

Predict and explain what happens when ethylamine is added to dilute hydrochloric acid.

Solution

Ethylamine, $\text{CH}_3\text{CH}_2\text{NH}_2$ , is a weak base because the nitrogen lone pair can accept a proton. Dilute hydrochloric acid supplies $\text{H}^+$ .

The amine accepts a proton to form the ethylammonium ion, producing a salt:

\text{CH}_3\text{CH}_2\text{NH}_2 + \text{HCl} \rightarrow \text{CH}_3\text{CH}_2\text{NH}_3^+\text{Cl}^-

This is an acid-base neutralisation; the basic amine is converted to its soluble salt, ethylammonium chloride.

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.

Treating amides as basic like amines

The key error is assuming amides are basic because they contain nitrogen; they are not, because the lone pair is tied up in the carbonyl. Another is muddling the formation: an amide forms from an acid plus an amine with loss of water, not from two amines. Always check whether the nitrogen lone pair is free (amine, basic) or delocalised (amide, not basic).

Exam-style questions

Questions in the style of SCSA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.

WACE 2022-style6 marks

The 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.

Show worked answer →

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 2020-style5 marks

Compare 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.

Show worked answer →

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.

Practise this

Sources & how we know this

Chemistry ATAR course: syllabus and support materials — SCSA
Chemistry: past ATAR course examinations — SCSA