CIE AS Chemistry (9701) exams from 2022

Revision Notes

3.3.3 Elimination Reactions of Halogenoalkanes

Halogenoalkanes: Elimination Reactions

  • In an elimination reaction, an organic molecule loses a small molecule
    • In the case of halogenoalkanes this small molecule is a hydrogen halide (eg. HCl)
  • The halogenoalkanes are heated with ethanolic sodium hydroxide causing the C-X bond to break heterolytically, forming an X ion and leaving an alkene as an organic product
    • For example, bromoethane reacts with ethanolic sodium hydroxide when heated to form ethene


Halogen Compounds Elimination, downloadable AS & A Level Chemistry revision notes

Hydrogen bromide is eliminated to form ethene

Exam Tip

The reaction conditions in a reaction are extremely important.

If NaOH(ethanol) is used, an elimination reaction takes place to form an alkene from a halogenoalkane.

If NaOH(aq) is used, a nucleophilic substitution reaction takes place to form an alcohol from a halogenoalkane.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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