Last updated: 24 August 2026
Amines can be thought of as organic relatives of ammonia. Start with an NH₃ molecule and replace one of its hydrogen atoms by a carbon-containing group, and you obtain an amine. In ethylamine, that group is an ethyl group; in phenylamine, nitrogen is attached directly to a benzene ring.
That apparently small structural change has a major effect on chemical behaviour. The key question throughout this chapter is therefore not simply whether nitrogen has a lone pair, but how available that lone pair is. Once you can answer that, the basicity and many of the reactions of amines become much easier to understand.
Try these five questions before reading the chapter. Pay particular attention to the nitrogen atom and its lone pair — much of amine chemistry follows from what happens to that electron pair.
- 5 diagnostic questions
- Structures and reaction schemes where useful
- Instant explanation for every answer option
What are amines?
Amines are organic compounds related structurally to ammonia, NH₃. One or more hydrogen atoms in ammonia are replaced by carbon-containing groups such as alkyl or aryl groups.
Two important examples at A-Level are ethylamine and phenylamine. They both contain an –NH₂ group, but the group attached to nitrogen is different, and that difference becomes crucial when we compare their basicity.
The key structural feature of an amine is a nitrogen atom with a lone pair of electrons that is available for bonding.
Ethylamine and phenylamine
Ethylamine, CH₃CH₂NH₂: nitrogen is attached to an ethyl group. It is therefore an example of an amine containing an alkyl group.
Phenylamine, C₆H₅NH₂: nitrogen is attached directly to a benzene ring. The interaction between the nitrogen lone pair and the π-electron system of the ring has an important effect on its basicity.
Do not confuse amines with amides
The names sound similar, but an amine and an amide are different functional groups. In an amine such as ethylamine, nitrogen is attached to carbon without an adjacent carbonyl group. In an amide such as ethanamide, nitrogen is attached directly to a carbonyl carbon.
A useful visual check is to look at the carbon directly attached to nitrogen. If nitrogen is attached to a C=O group, you are looking at an amide rather than an ordinary amine.
Preparation of amines
An important route to amines is the reduction of other nitrogen-containing compounds. The exact starting material determines the reagents and conditions that are required.
For the examples in this chapter, ethylamine can be prepared from either a nitrile or an amide, while phenylamine can be prepared by reducing nitrobenzene.
Preparing ethylamine from a nitrile
Ethanenitrile, CH₃CN, can be reduced to ethylamine, CH₃CH₂NH₂. One suitable reducing agent is LiAlH₄ in dry ether. Alternatively, hydrogen gas can be used with a nickel catalyst.
A nitrile can be reduced to a primary amine using LiAlH₄ in dry ether or H₂ with a nickel catalyst.
Preparing ethylamine from an amide
Ethanamide can also be reduced to ethylamine using LiAlH₄ in dry ether. During the reduction, the carbonyl portion of the amide is converted so that the carbonyl carbon becomes part of the carbon chain attached to nitrogen.
Preparing phenylamine from nitrobenzene
Phenylamine is prepared from nitrobenzene in two stages. First, nitrobenzene is heated with tin and concentrated hydrochloric acid. Under these acidic conditions, the nitrogen-containing product is present in its protonated salt form.
Aqueous sodium hydroxide is then added. The OH⁻ ions remove H⁺ from the phenylammonium ion, releasing the free amine, phenylamine.
Step 1: heat nitrobenzene with Sn and concentrated HCl. The nitro group is reduced and, because the mixture is acidic, the amine is obtained in protonated form.
Step 2: add NaOH(aq) to remove H⁺ from the phenylammonium ion and release phenylamine.
Why are amines basic?
Amines behave as bases because nitrogen possesses a lone pair of electrons. According to Lewis theory, a base is an electron-pair donor. The nitrogen lone pair can therefore be donated to H⁺ to form a new N–H bond.
The strength of an amine as a base depends on how readily this lone pair can be donated. Anything that increases the electron density around nitrogen tends to make protonation easier. Anything that makes the lone pair less available tends to reduce basicity.
Basicity depends on the availability of the nitrogen lone pair to accept H⁺.
Why is ethylamine more basic than ammonia?
In ethylamine, the nitrogen atom is attached to an ethyl group, –CH₂CH₃. Alkyl groups are electron-donating and exert a positive inductive effect.
The ethyl group pushes electron density towards the nitrogen atom. This increases the electron density associated with nitrogen and makes the lone pair more available for donation to H⁺.
Ammonia: the nitrogen lone pair is available for protonation, so NH₃ is basic.
Ethylamine: the ethyl group donates electron density towards nitrogen, making its lone pair still more available. Ethylamine is therefore more basic than ammonia.
Why is phenylamine less basic than ammonia?
Phenylamine behaves differently because the nitrogen atom is attached directly to a benzene ring. The lone pair on nitrogen can interact with the π-electron system of the ring and becomes delocalised.
Because the lone pair is spread into the benzene π system, it is less concentrated on nitrogen and therefore less available to form a bond with H⁺. Phenylamine is consequently a weaker base than ammonia.
Delocalisation of the nitrogen lone pair into the benzene ring makes phenylamine less basic.
When comparing basicity, avoid saying simply that “benzene makes phenylamine less basic”. The important explanation is that the nitrogen lone pair is delocalised into the benzene π-electron system, so it is less available to accept H⁺.
Comparing ethylamine, ammonia and phenylamine in water
For the three species considered here, the aqueous basicity order is:
| Base | Effect on nitrogen lone pair | Relative basicity |
|---|---|---|
| Ethylamine, CH₃CH₂NH₂ | Ethyl group donates electron density towards nitrogen | Most basic of the three |
| Ammonia, NH₃ | No alkyl electron-donating group and no aromatic delocalisation | Intermediate |
| Phenylamine, C₆H₅NH₂ | Nitrogen lone pair is delocalised into the benzene ring | Least basic of the three |
Basicity of alkylamines in the gaseous phase
In the gaseous phase, adding electron-donating alkyl groups increases electron density around nitrogen. For simple alkylamines, the trend is:
The important idea behind this trend is the positive inductive effect of alkyl groups. More alkyl groups attached to nitrogen increase electron density at nitrogen and make the lone pair more attractive to H⁺ in the gaseous phase.
Reactions of amines
The same nitrogen lone pair that explains the basicity of amines also explains several of their important reactions. Amines react with acids to form salts, phenylamine reacts readily with aqueous bromine, and primary amines react with acyl chlorides to form amides.
Reaction with acids: formation of ammonium salts
Since amines are bases, they accept H⁺ from acids. For example, ethylamine reacts with hydrochloric acid to form ethylammonium chloride.
The nitrogen lone pair is used to form a bond to H⁺. The amine molecule is therefore converted into a positively charged substituted ammonium ion.
Amine + acid → substituted ammonium salt.
Reaction of phenylamine with aqueous bromine
Phenylamine reacts very readily with aqueous bromine. The orange colour of bromine is decolourised and a white precipitate of 2,4,6-tribromophenylamine is formed.
The –NH₂ group strongly activates the benzene ring. The nitrogen lone pair is delocalised into the π-electron system of the ring, increasing electron density in the ring, particularly at the 2-, 4- and 6-positions. As a result, electrophilic substitution with bromine occurs readily at room temperature without the need for a halogen-carrier catalyst.
Observation: the orange colour of Br₂(aq) disappears.
Product: a white precipitate of 2,4,6-tribromophenylamine is formed.
Reaction with acyl chlorides: formation of amides
A primary amine can react with an acyl chloride to form an N-substituted amide. For a primary amine represented by RNH₂:
In this reaction, the nitrogen-containing amine becomes incorporated into the amide product. HCl is eliminated, so the overall process can be viewed as a condensation reaction.
When drawing the product, keep the carbonyl group from the acyl chloride and connect its carbonyl carbon to the nitrogen of the amine. The product is an amide, not another amine.
Common Mistakes
| Common mistake | Why it is wrong | Better approach |
|---|---|---|
| Saying ethylamine is more basic simply because it contains an ethyl group | The structural difference alone does not explain the change in basicity. | State that the ethyl group is electron-donating and increases electron density at nitrogen, making the lone pair more available to accept H⁺. |
| Saying phenylamine is less basic merely because it contains benzene | This does not explain what happens to the nitrogen lone pair. | Explain that the nitrogen lone pair is delocalised into the benzene π-electron system and is therefore less available for protonation. |
| Stopping after Sn / concentrated HCl when preparing phenylamine | Under the acidic reaction conditions, the amine is present in protonated form. | Add NaOH(aq) after the reduction to remove H⁺ and release phenylamine. |
| Confusing an amine with an amide | An amide contains a C=O group directly attached to nitrogen, whereas an ordinary amine does not. | Look for the carbonyl group before deciding which functional group is present. |
What you should be able to do
Recognise amines
Identify ethylamine and phenylamine and distinguish an amine from an amide.
Prepare primary amines
State the reagents used to reduce nitriles and amides to primary amines.
Prepare phenylamine
Describe the two-stage conversion of nitrobenzene to phenylamine using Sn / concentrated HCl followed by NaOH(aq).
Explain amine basicity
Relate basicity to the availability of the nitrogen lone pair and explain the effects of electron donation and delocalisation.
Compare important bases
Explain the aqueous basicity order ethylamine > ammonia > phenylamine.
Predict amine reactions
Describe salt formation with acids, bromination of phenylamine and amide formation with acyl chlorides.
These ten questions test whether you can apply the chapter to preparation, basicity, reactions and unfamiliar comparisons.
- 10 mastery questions
- Structures and reaction schemes where useful
- Instant explanation for every answer option
Frequently asked questions
Common Questions About Amines
Most questions about amines eventually return to the same idea: what is happening to the nitrogen lone pair? Keeping that in mind makes the apparently separate facts about preparation, basicity and reactions fit together much more naturally.
Why are amines bases?
Amines contain a lone pair of electrons on nitrogen. This lone pair can be donated to H⁺ to form a new N–H bond. Amines are therefore Lewis bases because they are electron-pair donors.
Why is ethylamine more basic than ammonia?
The ethyl group is electron-donating and pushes electron density towards the nitrogen atom through the positive inductive effect. This makes the nitrogen lone pair more available to accept H⁺, so ethylamine is more basic than ammonia.
Why is phenylamine less basic than ammonia?
In phenylamine, the nitrogen lone pair is delocalised into the π-electron system of the benzene ring. The lone pair is therefore less available to accept H⁺, making phenylamine a weaker base than ammonia.
Why is NaOH added after reducing nitrobenzene with Sn and concentrated HCl?
The reduction is carried out in strongly acidic conditions, so the amine is present as a protonated phenylammonium ion. Adding NaOH(aq) removes H⁺ from this ion and releases the free phenylamine.
What should I remember about the reaction between phenylamine and bromine water?
Phenylamine reacts rapidly with Br₂(aq) at room temperature. The orange bromine colour is decolourised and a white precipitate of 2,4,6-tribromophenylamine forms. The reaction occurs readily because the –NH₂ group strongly activates the benzene ring by donating electron density into its π-electron system.
Amines become much easier to understand once you follow the nitrogen lone pair. Electron donation makes it more available and increases basicity; delocalisation makes it less available to accept H⁺ but can also increase electron density in an attached benzene ring. The same lone pair therefore helps explain both the basicity and the characteristic reactions of amines.