Elimination Reactions of Halogenoalkanes (Cambridge (CIE) A Level Chemistry): Revision Note

Exam code: 9701

Last updated

Elimination Reactions of Halogenoalkanes

  • An elimination reaction involves the loss of a small molecule from a larger organic molecule

  • In halogenoalkanes, this small molecule is usually a hydrogen halide (e.g. HBr or HCl)

  • The product is typically an alkene

    • The elimination reaction of bromoethane with ethanolic sodium hydroxide

Reaction Conditions for Elimination

  • Halogenoalkanes are heated with ethanolic sodium hydroxide (NaOH dissolved in ethanol)

  • Under these anhydrous conditions, elimination occurs:

    • The C–X bond (where X = halogen) breaks heterolytically

    • A halide ion (X⁻) is released

    • A double bond forms, producing an alkene

  • E.g. Elimination of bromoethane:

bromoethane + sodium hydroxide (ethanol) → ethene + sodium bromide + water

C2H5Br + NaOH (ethanol) → C2H4 + NaBr + H2O

  • One hydrogen atom and the bromine atom are eliminated

  • The carbon chain forms a C=C double bond to make ethene

Examiner Tips and Tricks

Reaction conditions are crucial in determining the product.

Elimination = hot, ethanolic NaOH

Substitution = warm, aqueous NaOH

For teachers

Ready to test your students on this topic?

  • Create exam-aligned tests in minutes
  • Differentiate easily with tiered difficulty
  • Trusted for all assessment types
Explore Test Builder
Test Builder in a diagram showing questions being picked from different difficulties and topics, and being downloaded as a shareable format.