# Explain why 1,2-dichloroethene can exist as cis and trans stereoisomers, and describe one difference between the cis and trans forms of this molecule.

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

> 1,2-Dichloroethene has the molecular formula C₂H₂Cl₂ and contains a carbon-carbon double bond with a chlorine atom and a hydrogen atom attached to each carbon.

## Mark scheme (5 marks)

1. The C=C double bond restricts/prevents rotation
2. Each carbon in the double bond has two different groups attached to it
3. In the cis isomer the two chlorine atoms are on the same side of the double bond
4. In the trans isomer the two chlorine atoms are on opposite sides of the double bond
5. One valid difference between cis and trans 1,2-dichloroethene, e.g. different physical properties / different melting points or boiling points / different dipole moments

## Key terms

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

## 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/explain-why-1-2-dichloroethene-can-exist-as-5c1d321b) · Published by Druglandscape Ltd.