# Explain why primary amines are weaker bases than ammonia, yet aniline (phenylamine) is a significantly weaker base than both primary aliphatic amines and ammonia.

> IB DP Chemistry Higher Level (2023 syllabus) — S3.2 Functional groups: classification of organic compounds · Explain · 4 marks

> Amines are organic derivatives of ammonia in which one or more hydrogen atoms are replaced by carbon-containing groups. The base strength of an amine depends on the availability of the lone pair on nitrogen.

## Mark scheme (4 marks)

1. Primary aliphatic amines are weaker bases than ammonia because the alkyl group is electron-donating (by induction), which increases electron density on nitrogen and should increase base strength — award this mark only if the student correctly identifies that primary aliphatic amines are actually STRONGER bases than ammonia, correcting the stem's apparent misdirection, OR if the student states that alkyl groups donate electrons inductively, making the nitrogen lone pair more available.
2. In aniline, the lone pair on nitrogen is delocalised into the benzene ring (by conjugation / resonance), reducing its availability to accept a proton.
3. Because the lone pair is delocalised / less available, aniline is less able to donate the lone pair to a proton (H⁺), so it is a weaker base.
4. The anilinium ion (protonated aniline) loses the stabilisation by delocalisation because the lone pair is used in bonding to H⁺, so the equilibrium for protonation lies further to the left compared with aliphatic amines, confirming weaker base strength.

## Key terms

- [primary amine](https://www.gradenine.co.uk/glossary/primary-amine)
- [aniline](https://www.gradenine.co.uk/glossary/aniline)

## Related

- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-primary-amines-are-weaker-38733a32) · Published by Druglandscape Ltd.