Carbocations: Stability, Rearrangement and Neighbouring Groups · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

The restless positive carbon

Science · Chemistry · ages 19-20
Name ______________________   Date ____________

  1. What is hyperconjugation?

    • Overlap of neighbouring C-H bonds with the empty p orbital
    • Full transfer of an electron pair to the solvent
    • Breaking of the carbon skeleton

  2. Rank methyl, primary, secondary and tertiary carbocations from most to least stable.

    • Methyl, primary, secondary, tertiary
    • Tertiary, secondary, primary, methyl
    • All four are equally stable

  3. A carbocation is a true intermediate with a finite lifetime.

    Circle one:   True   False

  4. A neopentyl halide gives a product with a new skeleton. What does that fingerprint mean?

    • Direct attack kept the old shape
    • The nucleophile never arrived
    • A methyl shift before capture

  5. A secondary cation sits beside a tertiary carbon. What happens?

    • A hydride shift to the tertiary carbon
    • Nothing can ever move in a cation
    • The charge jumps straight to the solvent

  6. A lone pair next door reaches over as the leaving group departs. What changes?

    • Ionization slows and stereochemistry stays random
    • The reaction stops entirely
    • Faster ionization, attack from the back

  7. A substitution runs far faster than expected and gives one stereoisomer. What do you suspect?

    • A plain cation with no help
    • A neighbouring group speeding ionization and directing attack
    • A broken thermometer

  8. A student ranks a primary cation above a tertiary one because it is smaller. What is the error?

    • Size decides everything and the student is right
    • Donation and hyperconjugation favour tertiary
    • Cations cannot be ranked at all
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Answer key

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

The restless positive carbon W1-mt_0r1d2u30PE-s1

  1. Overlap of neighbouring C-H bonds with the empty p orbital · Shared electrons from next door calm the positive centre.
  2. Tertiary, secondary, primary, methyl · More alkyl neighbours means more donation and more hyperconjugation.
  3. True · It lives long enough to be captured, to shift, or to lose a proton.
  4. A methyl shift before capture · Unexpected skeletons fingerprint a rearrangement.
  5. A hydride shift to the tertiary carbon · Hydrogen migrates with its bonding pair toward greater stability.
  6. Faster ionization, attack from the back · The neighbour reshapes the valley and shields one face.
  7. A neighbouring group speeding ionization and directing attack · Speed plus direction is the neighbour signature.
  8. Donation and hyperconjugation favour tertiary · Electron supply beats smallness.
Worksheet · LightMySky