# Explain why hex-1-ene reacts with hydrogen bromide to produce predominantly 2-bromohexane rather than 1-bromohexane, including reference to the stability of the intermediate species involved.

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

## Mark scheme (4 marks)

1. The reaction proceeds via electrophilic addition, with H⁺ (or the δ+ hydrogen of HBr) acting as the electrophile attacking the C=C double bond in the first step.
2. Addition of H⁺ to C-1 generates a secondary carbocation at C-2, whereas addition to C-2 would generate a less stable primary carbocation at C-1.
3. The secondary carbocation is more stable than the primary carbocation because alkyl groups donate electron density inductively / hyperconjugation, delocalising the positive charge more effectively.
4. Br⁻ (the nucleophile) then attacks the more stable secondary carbocation at C-2, giving 2-bromohexane as the major product, in accordance with Markovnikov's rule.

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-hex-1-ene-reacts-with-hydrogen-f5c6b262) · Published by Druglandscape Ltd.