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AS · Practice questions · Types of organic reaction and mechanism

Name the mechanism.

Six original Cambridge-style questions on organic reaction types and the language of mechanisms.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Arrows move pairs of electrons.

01
Recall
[2 marks]

Define nucleophile and electrophile, giving one example of each.

  • Nucleophile: an electron-pair donor, e.g. OH−, CN−, NH3. ✓
  • Electrophile: an electron-pair acceptor, e.g. H+, NO2+, Brδ+. ✓
02
Recall
[2 marks]

Distinguish between homolytic and heterolytic fission of the Cl–Cl bond, writing the products.

  • Homolytic: Cl–Cl → 2Cl• (one electron to each atom; free radicals). ✓
  • Heterolytic: Cl–Cl → Cl+ + Cl− (both electrons to one atom; ions). ✓
03
Analysis
[3 marks]

Classify each reaction: (a) C2H4 + HBr → C2H5Br; (b) C2H5OH → C2H4 + H2O; (c) CH3Br + OH− → CH3OH + Br−.

  • (a) addition (electrophilic addition). ✓
  • (b) elimination (dehydration). ✓
  • (c) substitution (nucleophilic substitution). ✓
04
Analysis
[3 marks]

Describe the curly arrows needed for OH− reacting with bromoethane in one step.

  • Show C–Br as polar, Cδ+ and Brδ−. ✓
  • Arrow from a lone pair on O of OH− to the δ+ carbon. ✓
  • Arrow from the C–Br bond to Br, forming Br−. ✓
05
Recall
[2 marks]

Define free radical and carbocation.

  • Free radical: a species with an unpaired electron. ✓
  • Carbocation: an ion with a positively charged carbon atom. ✓
06
Explain
[2 marks]

Explain why the carbon atom in C–Br is attacked by nucleophiles but the carbon atoms in C=C are attacked by electrophiles.

  • Br is more electronegative, so the carbon in C–Br is δ+ and attracts electron-pair donors. ✓
  • A C=C bond is a region of high electron density (the π electrons), which attracts electron-pair acceptors. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.