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AS · Practice questions · Structural isomerism

Rearrange the atoms.

Six original Cambridge-style questions on structural isomerism.

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

Same formula, different connections.

01
Recall
[1 marks]

Define structural isomers.

  • Compounds with the same molecular formula but different structural formulae. ✓
02
Analysis
[3 marks]

Draw and name the three structural isomers of C5H12.

  • Pentane, CH3CH2CH2CH2CH3. ✓
  • 2-methylbutane, (CH3)2CHCH2CH3. ✓
  • 2,2-dimethylpropane, C(CH3)4. ✓
03
Analysis
[3 marks]

Draw and name three isomers of C3H8O and state the type of isomerism between each pair.

  • Propan-1-ol CH3CH2CH2OH and propan-2-ol CH3CH(OH)CH3: positional. ✓
  • Methoxyethane CH3OCH2CH3. ✓
  • Either alcohol with methoxyethane: functional group isomers. ✓
04
Analysis
[4 marks]

Draw the four structural isomers of C4H9Br.

  • 1-bromobutane: CH3CH2CH2CH2Br. ✓
  • 2-bromobutane: CH3CHBrCH2CH3. ✓
  • 1-bromo-2-methylpropane: (CH3)2CHCH2Br. ✓
  • 2-bromo-2-methylpropane: (CH3)3CBr. ✓
05
Analysis
[2 marks]

Give the structures of an aldehyde and a ketone with the formula C4H8O.

  • Aldehyde: butanal, CH3CH2CH2CHO (or 2-methylpropanal). ✓
  • Ketone: butanone, CH3COCH2CH3. ✓
06
Explain
[2 marks]

Explain why butane (b.p. −1 °C) has a higher boiling point than methylpropane (b.p. −12 °C).

  • Both have the same number of electrons. ✓
  • The unbranched butane molecules have a larger surface contact, so stronger id-id forces must be overcome. ✓

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.