Elimination and Choosing Between Two Pathways · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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One reagent, two pathways

Science · Chemistry · ages 16-18
Name ______________________   Date ____________

  1. Which conditions favour substitution?

    • Hot concentrated strong base
    • Cool and dilute, with a weak base
    • Bulky base with a crowded substrate

  2. What forms when hydroxide acts as a base toward a haloalkane?

    • An alcohol by substitution
    • An alkene by elimination
    • An amine by substitution

  3. Which conditions favour elimination?

    • Dilute cool weak base
    • Polar solvent with a weak base
    • Hot, concentrated strong base

  4. What does it mean to call hydroxide both a nucleophile and a base?

    • It can attack carbon to substitute or grab a hydrogen to eliminate
    • It can only ever substitute
    • It changes element between reactions

  5. What changes between hydrolysing bromopropane and making propene from it?

    • The halogen changes from bromine to chlorine
    • Only the conditions change
    • Propene needs a different halogen entirely

  6. A bulky base favours substitution because it reaches carbon easily.

    Circle one:   True   False

  7. A student draws elimination with hydroxide bonding to carbon. What is the error?

    • That arrow shows substitution
    • Hydroxide can never touch a haloalkane
    • Elimination has no arrows at all

  8. Two alkenes can form from one haloalkane. Which is usually the major product?

    • The least substituted alkene
    • Always the Z isomer
    • The more substituted alkene
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Answer key

For grown-ups. Fold this page away before handing over the rest.

One reagent, two pathways W1-mt_tRj_kiSS51-s1

  1. Cool and dilute, with a weak base · Gentle conditions let attack on carbon win.
  2. An alkene by elimination · As a base it grabs a hydrogen and the double bond forms.
  3. Hot, concentrated strong base · Strong, hot and concentrated pushes hydroxide to grab hydrogen.
  4. It can attack carbon to substitute or grab a hydrogen to eliminate · The same species plays two roles with two targets.
  5. Only the conditions change · The starting pair stays the same. Only the conditions change, and they pick the pathway.
  6. False · A bulky base struggles to reach carbon but can still pluck an exposed hydrogen.
  7. That arrow shows substitution · Bonding to carbon is substitution; elimination pulls a hydrogen off the neighbour.
  8. The more substituted alkene · Extra alkyl groups steady the double bond, favouring the more substituted alkene.
Worksheet · LightMySky