# 2-Bromobut-2-ene can exist as cis and trans stereoisomers. Explain why 2-bromobut-2-ene can form cis and trans isomers, and describe how the cis and trans isomers of 2-bromobut-2-ene differ from each other.

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

> 2-Bromobut-2-ene has the molecular formula C₄H₇Br and contains a carbon–carbon double bond.

## Mark scheme (5 marks)

1. The molecule contains a carbon–carbon double bond (C=C)
2. There is no free rotation about the carbon–carbon double bond
3. Each carbon of the double bond has two different groups attached to it
4. In the cis isomer, the two identical/similar groups (e.g. the two methyl groups or the two larger groups) are on the same side of the double bond
5. In the trans isomer, the two identical/similar groups are on opposite sides of the double bond

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/2-bromobut-2-ene-can-exist-as-cis-and-0c94131c) · Published by Druglandscape Ltd.