# Pent-2-ene can exist as cis and trans stereoisomers. Explain why pent-2-ene can form cis and trans isomers, and state one difference between the cis and trans forms of pent-2-ene.

> Eduqas A-Level Chemistry — 4.1 Stereoisomerism · Explain · 5 marks

> Pent-2-ene has the molecular formula C₅H₁₀ and contains a carbon–carbon double bond between carbon-2 and carbon-3.

## Mark scheme (5 marks)

1. There is restricted rotation about the carbon–carbon double bond
2. Each carbon of the double bond has two different groups attached to it
3. In the cis isomer the two larger/similar groups are on the same side of the double bond
4. In the trans isomer the two larger/similar groups are on opposite sides of the double bond
5. Cis and trans isomers have different physical properties, e.g. different boiling points / melting points

## Key terms

- [stereoisomers](https://www.gradenine.co.uk/glossary/stereoisomers)
- [trans isomer](https://www.gradenine.co.uk/glossary/trans-isomer)

## Related

- [Revision notes for Eduqas A-Level Chemistry](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/pent-2-ene-can-exist-as-cis-and-052d4f56) · Published by Druglandscape Ltd.