IB Chemistry HL 3.4.12 Carbocation Stability Question Bank

Practise IB Chemistry HL 3.4.12 with questions using carbocation stability to predict and explain major products.

Exam points

draw the alternative carbocations formed by protonation at either alkene carbon
rank tertiary, secondary and primary carbocations by alkyl-group stabilisation
derive the major product from nucleophilic attack on the more stable carbocation

[Maximum number: 2]

Ethanol is obtained by the hydration of ethene, $\mathrm{C}_{2} \mathrm{H}_{4}$ .

Alternative synthetic routes exist to produce alcohols.

Explain why the major organic product is 2-bromopropane and not 1-bromopropane.

«2-bromopropane involves» formation of more stable «secondary» carbocation/carbonium ion/intermediate

OR

1-bromopropane involves formation of less stable «primary» carbocation/ carbonium ion/intermediate «increased» positive inductive/electron-releasing effect of extra -R group/- $\mathrm{CH}_{3}$ /methyl «increases stability of secondary carbocation»

Marking guidance:

Award [1] for "more stable due to positive inductive effect".

Do not award marks for quoting Markovnikov's rule without any explanation.

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3.4.12 (HL)—Carbocation stability question 1