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.

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