Electrophilic Addition to Alkenes · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How alkenes invite attack

Science · Chemistry · ages 16-17
Name ______________________   Date ____________

  1. Where does the first curly arrow start?

    • On the electrophile
    • On a spectator ion
    • On the double bond

  2. Why does an electrophile attack a double bond?

    • High electron density draws it in
    • Double bonds carry a full positive charge
    • Electrophiles attack single bonds first

  3. How does non-polar bromine become able to attack?

    • It is already fully charged
    • The double bond polarises it
    • Bromine splits into ions on its own

  4. Why is a secondary carbocation more stable than a primary one?

    • More alkyl groups steady it more
    • It carries more hydrogen atoms
    • Primary carbons cannot hold any charge

  5. H adds to the end carbon of propene. Which carbocation forms?

    • A primary one
    • A secondary one
    • A tertiary one

  6. The major product of HBr with propene is 1-bromopropane.

    Circle one:   True   False

  7. A student predicts the primary carbocation route gives the major product because it forms faster. What is the error?

    • Stability favours the secondary route
    • Carbocations never form in this mechanism
    • Both routes give exactly equal amounts

  8. What adds across the double bond with concentrated sulfuric acid, and what follows?

    • Two bromines, and nothing follows
    • H plus HSO4 add, then hydrolysis
    • Water only, giving an alkane
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Answer key

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

How alkenes invite attack W1-mt_1RB5nj8zR8-s1

  1. On the double bond · The arrow tracks the pi pair, which lives on the double bond.
  2. High electron density draws it in · High electron density draws the electrophile in.
  3. The double bond polarises it · Repulsion of bromine electrons leaves the nearer end slightly positive.
  4. More alkyl groups steady it more · Extra alkyl groups steady the positive centre.
  5. A secondary one · Hydrogen on the end leaves the positive charge on the middle carbon with two alkyl neighbours.
  6. False · The secondary route wins, giving 2-bromopropane as the major product.
  7. Stability favours the secondary route · Stability decides: the secondary path wins and sets the major product.
  8. H plus HSO4 add, then hydrolysis · The acid adds by the same mechanism and hydrolysis finishes to the alcohol.
Worksheet · LightMySky