AS Level Chemistry chapter 13: An introduction to AS Level organic chemistry MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

92 exam-style questions on An introduction to AS Level organic chemistry, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

92 questions · 4 topics · 10 per test

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What chapter 13 covers

Ten An introduction to AS Level organic chemistry questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. In the reaction of methane with chlorine in ultraviolet light, which equation is a termination step?

  1. A
    Cl2 → 2Cl•
  2. B
    CH4 + Cl• → CH3• + HCl
  3. C
    CH3• + Cl2 → CH3Cl + Cl•
  4. D
    CH3• + Cl• → CH3Cl
Show answer

Answer: D. Termination removes free radicals: two radicals combine to form a molecule. Splitting Cl2 is initiation, and the steps in which one radical produces another are propagation.

2. How is a π bond between two carbon atoms formed?

  1. A
    by end-on overlap of an s orbital and a p orbital
  2. B
    by end-on overlap of two sp2 hybrid orbitals
  3. C
    by sideways overlap of two sp3 hybrid orbitals
  4. D
    by sideways overlap of two unhybridised p orbitals
Show answer

Answer: D. Each sp2 carbon keeps one unhybridised p orbital at right angles to the plane; these overlap sideways above and below the C–C axis to form the π bond. End-on overlap of hybrid orbitals forms the σ bond.

3. Propanal reacts with HCN in the presence of a trace of KCN. Which describes the first step of the mechanism and the intermediate formed?

  1. A
    CN− attacks the δ+ carbonyl carbon; the intermediate has a negative charge on oxygen.
  2. B
    H+ attacks the carbonyl oxygen; the intermediate is a carbocation.
  3. C
    CN− attacks the carbonyl oxygen; the intermediate has a negative charge on carbon.
  4. D
    A CN• radical adds to the C=O bond; the intermediate is a radical.
Show answer

Answer: A. In nucleophilic addition the nucleophile CN− donates a lone pair to the δ+ carbon and the π electrons of C=O move onto oxygen, giving an alkoxide ion; this then takes H+ from HCN, regenerating CN−.

4. An alkene X has the molecular formula C4H8. X reacts with hydrogen bromide to give only one structural isomer of C4H9Br. What is X?

  1. A
    but-1-ene
  2. B
    but-2-ene
  3. C
    methylpropene
  4. D
    cyclobutane
Show answer

Answer: B. But-2-ene, CH3CH=CHCH3, is symmetrical, so H and Br adding either way round both give 2-bromobutane. But-1-ene and methylpropene are unsymmetrical and can give two products; cyclobutane is not an alkene.

5. Which statement correctly describes a nucleophile?

  1. A
    an electron-pair acceptor attracted to regions of high electron density
  2. B
    any positively charged ion
  3. C
    a species with an unpaired electron
  4. D
    a species with a lone pair of electrons that it donates to an electron-deficient atom
Show answer

Answer: D. Nucleophile means nucleus-loving: it seeks a δ+ centre and donates an electron pair to form a new bond, e.g. OH−, CN− or NH3. An electron-pair acceptor is an electrophile.

6. Which statement describes the members of a homologous series?

  1. A
    They have the same molecular formula but different structural formulae.
  2. B
    They have identical physical properties, such as boiling point.
  3. C
    They have the same general formula and functional group, and successive members differ by CH2.
  4. D
    They contain the same number of carbon atoms but different functional groups.
Show answer

Answer: C. A homologous series shares a general formula and functional group, so its members have similar chemical properties; each member differs from the next by CH2. Physical properties such as boiling point change gradually along the series; same molecular formula describes isomers.

7. A hydrocarbon has the molecular formula C5H10. It does not decolourise bromine water. Which description fits this hydrocarbon?

  1. A
    a straight-chain alkane
  2. B
    a cyclic alkane
  3. C
    a branched alkene
  4. D
    a straight-chain alkene
Show answer

Answer: B. C5H10 fits CnH2n, so it has either one C=C or one ring. As it does not react with bromine water it has no C=C, so it must be cyclic (e.g. cyclopentane). An open-chain alkane with 5 C would be C5H12.

8. In the mechanism of the reaction between hydroxide ions and bromoethane, which curly arrow shows the attack by the nucleophile?

  1. A
    from the lone pair on the oxygen atom of OH− to the carbon atom bonded to bromine
  2. B
    from the C–Br bond to the bromine atom
  3. C
    from the carbon atom bonded to bromine to the oxygen atom of OH−
  4. D
    from a lone pair on the bromine atom to the hydrogen atom of OH−
Show answer

Answer: A. A curly arrow starts at an electron pair: OH− donates a lone pair to the δ+ carbon. The arrow from the C–Br bond to Br is also in the mechanism, but it shows the leaving group departing, not the nucleophile attacking.

9. In which molecule do all the atoms lie in the same plane?

  1. A
    ethane
  2. B
    ethene
  3. C
    propene
  4. D
    cyclohexane
Show answer

Answer: B. In ethene both carbons are sp2 and the π bond prevents rotation, so all six atoms are coplanar. Propene has a tetrahedral CH3 group, and ethane and cyclohexane contain only sp3 carbons.

10. Which compound is NOT a hydrocarbon?

  1. A
    propene
  2. B
    cyclopentane
  3. C
    propan-2-ol
  4. D
    2-methylpropane
Show answer

Answer: C. A hydrocarbon contains carbon and hydrogen only. Propan-2-ol, CH3CH(OH)CH3, also contains oxygen.

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How many An introduction to AS Level organic chemistry MCQs are there?

92, each with the answer and a short explanation, across 4 topics: Formulas, functional groups and the naming of organic compounds, Characteristic organic reactions, Shapes of organic molecules; σ and π bonds, Isomerism: structural isomerism and stereoisomerism. Every chapter test draws ten of them, so you can take it many times.

Is the AS Level Chemistry chapter 13 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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