Introduction to organic chemistryAQA A-Level Chemistry: Topic test

1. 1
   A flavour chemist records the structure of an organic compound used in food flavourings: CH₃CH₂CH(CH₃)CH₂CHO.

   (a)

   What is the IUPAC name of this compound?

   [1 mark]

   • A3-ethylbutanal
   • B3-methylpentanal
   • C4-methylpentanal
   • D3-methylpentanol

   (b)

   What is the general formula of the homologous series to which this compound belongs?

   [1 mark]

   • ACₙH₂ₙ₊₂O
   • BCₙH₂ₙO₂
   • CCₙH₂ₙ₊₁O
   • DCₙH₂ₙO

   (c)

   Explain what is meant by a homologous series, and state whether this compound and butanal, CH₃CH₂CH₂CHO, belong to the same homologous series.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Chloromethane, CH₃Cl, reacts with hydroxide ions to give methanol and chloride ions: CH₃Cl + OH⁻ → CH₃OH + Cl⁻. The mechanism is a single step in which the hydroxide ion attacks the carbon atom as the C–Cl bond breaks.

   (a)

   From which part of the hydroxide ion does the curly arrow showing attack on the carbon atom start?

   [1 mark]

   • AA lone pair of electrons on the oxygen atom
   • BThe hydrogen atom
   • CThe middle of the O–H bond
   • DThe carbon atom of chloromethane

   (b)

   How does the C–Cl bond break in this reaction?

   [1 mark]

   • AHomolytically, forming a carbon radical and a chlorine radical
   • BHeterolytically, with both electrons of the bond going to carbon
   • CHeterolytically, with both electrons of the bond going to chlorine
   • DHomolytically, with both electrons of the bond going to chlorine

   (c)

   Describe how a curly arrow is used to show the breaking of the C–Cl bond in this mechanism, and state the species formed from the chlorine atom.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Hexane, C₆H₁₄, is used as a solvent for extracting vegetable oils. It is one of five alkanes that share this molecular formula.

   (a)

   Define the term structural isomers, and identify the type of structural isomerism shown by hexane and 2,2-dimethylbutane.

   [3 marks]

   (b)

   Give the structural formula and IUPAC name of each of the two other isomers of hexane that contain a single methyl branch on the main carbon chain.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Compounds with molecular formula C₆H₁₂ include hex-2-ene, P, CH₃CH=CHCH₂CH₂CH₃, and 2-methylpent-2-ene, Q, (CH₃)₂C=CHCH₂CH₃. Two further compounds with this formula are R, CH₂=CHCH₂CH₂CH₂CH₃, and a ring compound S in which six carbon atoms are joined in a ring by single bonds only.

   (a)

   Explain why P shows E-Z isomerism but Q does not. Use the Cahn-Ingold-Prelog priority rules to name the isomer of P in which the CH₃ group and the CH₂CH₂CH₃ group are on the same side of the double bond.

   [6 marks]

   (b)

   Name R and S, and identify the type of structural isomerism between P and R, between P and Q, and between P and S. State what all four compounds have in common that makes them structural isomers of one another.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   Methane reacts with bromine in ultraviolet light to form bromomethane and hydrogen bromide by a free-radical substitution mechanism: CH₄ + Br₂ → CH₃Br + HBr.

   (a)

   What is a free radical?

   [1 mark]

   • AA negatively charged ion with a lone pair
   • BAn atom with a full outer shell of electrons
   • CA species that donates a pair of electrons to form a covalent bond
   • DA species with an unpaired electron

   (b)

   Which equation represents a propagation step in this reaction?

   [1 mark]

   • ABr₂ → 2Br•
   • BCH₃• + Br• → CH₃Br
   • CCH₄ + Br• → CH₃• + HBr
   • DCH₃• + CH₃• → C₂H₆

   (c)

   Explain why ultraviolet light is needed for this reaction and what is meant by homolytic fission.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   3-Methylpent-2-ene, CH₃CH=C(CH₃)CH₂CH₃, shows E-Z isomerism.

   (a)

   Which feature of the molecule causes E-Z isomerism?

   [1 mark]

   • ARestricted rotation about the C=C bond, with two different groups on each carbon
   • BFree rotation about the C–C single bonds
   • CA chiral carbon atom with four different groups
   • DThe different numbers of hydrogen atoms in the isomers

   (b)

   Which group has the higher CIP priority on carbon 3?

   [1 mark]

   • ACH₃, because it has the lower relative mass
   • BCH₂CH₃, because its first carbon is attached to (C, H, H) rather than (H, H, H)
   • CNeither: both groups are attached through carbon, so they have equal priority
   • DCH₃, because it is nearer the double bond

   (c)

   Name the isomer in which the CH₃ group on carbon 2 and the CH₂CH₃ group on carbon 3 are on the same side of the double bond. Use CIP priorities to justify the name.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A laboratory data sheet lists an organic compound X with the structural formula CH₃CH(Cl)CH₂CH(OH)CH₃.

   (a)

   Give the IUPAC name of X and explain how the carbon atoms of the chain are numbered.

   [3 marks]

   (b)

   Give the structural formula of each of the following compounds: (i) 3-methylbut-1-ene, (ii) 2-bromo-2-methylpropane, (iii) pentan-3-one, (iv) cyclohexanol.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   Propane, CH₃CH₂CH₃, reacts with chlorine in ultraviolet light by free-radical substitution to give a mixture of products that includes two monochloropropanes.

   (a)

   Write equations for the initiation step, the two propagation steps that form 1-chloropropane, and a termination step that forms a hydrocarbon. Explain the role of ultraviolet light and why the second propagation step keeps the reaction going.

   [6 marks]

   (b)

   Name the two monochloropropanes and state the type of isomerism they show. Write the two propagation steps that form the second isomer, explain how a dichloropropane can form, and suggest how this can be reduced.

   [6 marks]

   Total for question 8: 12 marks

End of questions