# Explain why benzene undergoes electrophilic substitution with concentrated nitric acid in the presence of concentrated sulfuric acid, rather than electrophilic addition, and identify the electrophile responsible for the reaction.

> IB DP Chemistry Standard Level (2023 syllabus) — R3.3 Electron sharing reactions · Explain · 4 marks

> Benzene reacts with a mixture of concentrated nitric acid and concentrated sulfuric acid to form nitrobenzene. The reaction preserves the ring structure of benzene.

## Mark scheme (4 marks)

1. The electrophile is the nitronium ion (NO₂⁺), generated when sulfuric acid protonates nitric acid.
2. Benzene has a delocalised pi electron system / ring of delocalised electrons above and below the plane that attracts electrophiles.
3. Addition would disrupt / destroy the delocalised electron system / aromaticity, which is energetically unfavourable.
4. Substitution allows the delocalised system / aromaticity to be restored / retained when the proton is lost in the second step, making it the preferred pathway.

## Key terms

- [electrophilic substitution](https://www.gradenine.co.uk/glossary/electrophilic-substitution)

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-benzene-undergoes-electrophilic-substitution-76ea20f2) · Published by Druglandscape Ltd.