Organic Chemistry: ArenesEdexcel International A Level Chemistry: Topic test

20 questions, 54 marks

Edexcel International A Level Chemistry

Organic Chemistry: Arenes topic test

Total 54 marks

Name

Class

Date

1
Benzene, C₆H₆, has a planar ring of six carbon atoms. Each carbon atom forms three sigma bonds, to two other carbon atoms and to one hydrogen atom, and has one electron in a p orbital.
(a)
What is the H–C–C bond angle in benzene?
[1 mark]
A109.5°
B90°
C120°
D180°
(b)
Which statement describes the pi bonding in benzene?
[1 mark]
AThe p orbitals overlap sideways above and below the plane of the ring, forming a ring of delocalised electron density
BThe p orbitals overlap sideways to form three separate localised pi bonds between alternate carbon atoms
CThe p orbitals overlap end-on along the axes of the carbon–carbon bonds
DThe pi electrons are concentrated in the plane of the ring between the carbon nuclei
(c)
Kekulé suggested a ring with alternating single and double bonds. A student records the infrared spectrum of benzene and finds no absorption in the range 1620–1680 cm⁻¹, where alkenes absorb because of the C=C bond. Explain what this shows about Kekulé's structure.
[2 marks]
Total for question 1: 4 marks
2
Benzene reacts with chloromethane, CH₃Cl, in the presence of anhydrous aluminium chloride, AlCl₃, to form methylbenzene, C₆H₅CH₃, and hydrogen chloride.
(a)
What is the role of the aluminium chloride in this reaction?
[1 mark]
AIt acts as a nucleophile that attacks benzene
BIt is a catalyst that accepts a lone pair from chlorine, helping to generate the electrophile
CIt is a reducing agent that converts benzene into a radical
DIt is a dehydrating agent that removes water from the products
(b)
Which equation shows the generation of the electrophile in this reaction?
[1 mark]
ACH₃Cl + AlCl₃ → CH₃⁻ + AlCl₄⁺
BCH₃Cl + AlCl₃ → CH₃• + •AlCl₄
CAlCl₃ + Cl₂ → AlCl₄⁻ + Cl⁺
DCH₃Cl + AlCl₃ → CH₃⁺ + AlCl₄⁻
(c)
When the benzene ring attacks the electrophile, an intermediate forms. Describe what happens to the delocalised pi system in the intermediate, and explain why the intermediate then loses a hydrogen ion rather than adding another group.
[2 marks]
Total for question 2: 4 marks
3
A teaching laboratory prepares 2,4,6-tribromophenol, C₆H₂Br₃OH (Mr = 330.7), by adding excess bromine water to 40.0 cm³ of a 0.0250 mol dm⁻³ aqueous solution of phenol, C₆H₅OH. The student collects 0.287 g of dry product. Br₂ = 159.8 g mol⁻¹.
(a)
Calculate the percentage yield of 2,4,6-tribromophenol.
[3 marks]
(b)
Write the equation for the reaction of phenol with bromine water. Calculate the minimum volume, in cm³, of 0.0500 mol dm⁻³ bromine water needed to react with all of the phenol in the 40.0 cm³ sample.
[4 marks]
Total for question 3: 7 marks
4
Benzene, C₆H₆, is resistant to the addition reactions that are typical of alkenes. Its characteristic reactions are electrophilic substitutions, such as nitration with a mixture of concentrated nitric acid and concentrated sulfuric acid.
(a)
Explain, in terms of orbital overlap and electron density, why benzene resists addition with bromine, in contrast with an alkene such as cyclohexene, and why substitution is preferred.
[6 marks]
(b)
Describe the mechanism for the nitration of benzene, including the equation for the generation of the electrophile and the role of the concentrated sulfuric acid.
[6 marks]
Total for question 4: 12 marks
5
Benzene reacts with fuming sulfuric acid (oleum), which contains dissolved sulfur trioxide, SO₃. The product is benzenesulfonic acid, C₆H₅SO₃H.
(a)
Which species acts as the electrophile in this reaction?
[1 mark]
AHSO₄⁻
BH₂SO₄
CSO₄²⁻
DSO₃
(b)
Why is sulfur trioxide able to act as an electrophile?
[1 mark]
AThe sulfur atom has a lone pair of electrons
BThe sulfur atom is electron-deficient because it is bonded to three highly electronegative oxygen atoms
CThe molecule carries an overall negative charge
DThe S–O bonds are non-polar
(c)
Write the equation for the reaction of benzene with sulfur trioxide, and name the type of mechanism.
[2 marks]
Total for question 5: 4 marks
6
Benzene reacts with propanoyl chloride, CH₃CH₂COCl, in the presence of anhydrous aluminium chloride, AlCl₃, under reflux. The organic product is a ketone and hydrogen chloride is also formed.
(a)
Which species is the electrophile that attacks the benzene ring?
[1 mark]
ACH₃CH₂CO⁺
BCH₃CH₂COCl
CAlCl₄⁻
DCH₃CH₂CO⁻
(b)
What is the organic product of this reaction?
[1 mark]
APropylbenzene, C₆H₅CH₂CH₂CH₃
BPhenyl propanoate, C₆H₅OCOCH₂CH₃
C1-Phenylpropan-1-one, C₆H₅COCH₂CH₃
DPhenylethanone, C₆H₅COCH₃
(c)
Explain why the reaction mixture must be kept free from water.
[2 marks]
Total for question 6: 4 marks
7
A student reacts 7.80 g of benzene (Mr = 78.0) with excess bromine in the presence of anhydrous iron(III) bromide, FeBr₃, and obtains 10.2 g of bromobenzene, C₆H₅Br (Mr = 157.0).
(a)
Calculate the percentage yield of bromobenzene.
[3 marks]
(b)
(i) Write the equation for the generation of the electrophile from bromine and iron(III) bromide. [1]
(ii) State the role of iron(III) bromide in this step. [1]
(iii) Write the equation for the regeneration of the catalyst in the final step of the mechanism. [1]
(iv) State the role of benzene in the mechanism. [1]
[4 marks]
Total for question 7: 7 marks
8
Benzene, C₆H₆, burns in air with a smoky flame. A student also compares how benzene and phenol, C₆H₅OH, react with bromine.
(a)
Explain why benzene burns with a smoky flame in air. Include a balanced equation for its complete combustion and a comparison with hexane, C₆H₁₄.
[6 marks]
(b)
Compare the conditions needed to brominate benzene and phenol, and explain the difference in terms of electron density. State how the products differ.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).