A Level Official Exam Material
FREE Past Paper Questions by Topic
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Unit 5: Transition Metals and
Organic Nitrogen Chemistry
Topic 18: Organic Chemistry – Arenes
For A Level students only
Q1. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
The reaction of ethene with bromine occurs under normal laboratory conditions but the reaction of benzene with bromine to form bromobenzene requires heat and the presence of a catalyst.
The best explanation for the difference in reactivity is that the delocalised electrons in benzene
A repel electrophiles
B result in a kinetic barrier to intermediate formation
C result in benzene having an endothermic enthalpy of formation
D make benzene thermodynamically stable with respect to the formation of bromobenzene
(Total for question = 1 mark)
Q2. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
What is the product when benzene reacts with fuming sulfuric acid?
Q3. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
Which of these could not be formed when excess benzene is heated with trichloromethane, CHCl3, in the presence of an aluminium chloride catalyst?
Q4. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
The delocalised electrons in benzene result from the overlap of
A s orbitals to form σ bonds
B s orbitals to form π bonds
C p orbitals to form σ bonds
D p orbitals to form π bonds
(Total for question = 1 mark)
Q5. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
Benzene is sometimes represented by a Kekulé structure.
If this were the only structure of benzene, what would be the total number of isomers of dichlorobenzene?
A two
B three
C four
D five
(Total for question = 1 mark)
Q6. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
What is the molar mass, in g mol–1 , of the organic product when phenol reacts with excess bromine water?
A 156.9
B 172.9
C 330.7
D 488.5
(Total for question = 1 mark)
Q7. For each question, select one answer from A to D and put a cross in the box .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross . Methylbenzene reacts with a mixture of concentrated nitric acid and concentrated sulfuric acid to form 2,4,6-trinitromethylbenzene.
(a) What is the number of peaks in the 13C NMR spectrum of methylbenzene? (1)
A seven
B six
C five
D four
(b) What type of reaction takes place? (1)
A nucleophilic addition
B nucleophilic substitution
C electrophilic addition
D electrophilic substitution
(c) Which expression shows the mass in grams of 2,4,6-trinitromethylbenzene formed from 10 g of methylbenzene if the yield of the reaction is 85 %?
[Mr values: methylbenzene = 92 2,4,6-trinitromethylbenzene = 227] (1)
A (10 × 85 × 227) ÷ (92 × 100)
B (10 × 100 × 227) ÷ (92 × 85)
C (10 × 100 × 227) ÷ (92 × 115)
D (10 × 115 × 227) ÷ (92 × 100)
(Total for question = 3 marks)
Q8. This question is about benzene and some related compounds. (a) Some standard enthalpies of combustion are shown.
(i) Using the standard enthalpies of combustion of cyclohexene and cyclohexa-1,4-diene, calculate a value for the enthalpy of combustion of the theoretical compound 'cyclohexa-1,3,5-triene'. (2)
(ii) Explain the difference between the enthalpy of combustion of 'cyclohexa-1,3,5-triene' calculated in (a)(i) and the enthalpy of combustion of benzene given in the table. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(b) Bromine reacts with cyclohexene to form 1,2-dibromocyclohexane, and with benzene to form bromobenzene.
Compare and contrast these reactions, considering the type and mechanism of each reaction and the conditions required.
You are not required to draw the mechanisms of the reactions. (4) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(c) Bromine also reacts with phenol.
(i) Identify, by name or formula, the organic product when phenol reacts with excess bromine. (1) .............................................................................................................................................
(ii) Explain why bromine reacts much faster with phenol than with benzene. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(Total for question = 12 marks)
Q9. This question is about benzene, C6H6, a colourless liquid first isolated in 1825, and some related compounds.
Three C6H6 structures proposed in the 1860s are shown.
The Dewar and Ladenburg structures have since been isolated as stable compounds but there is no compound with the Kekulé structure.
(a) Describe a chemical test, including the result, that could distinguish the Dewar structure from benzene. (2) ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(b) State one similarity and one difference you would expect in the low resolution proton NMR spectrum of the Ladenburg structure and that of benzene.
You must include data from the Data Booklet to support your answer. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(c) Explain how X-ray diffraction shows that benzene has a delocalised structure and not a Kekulé structure. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(d) The Ladenburg and Dewar structures both isomerise to benzene.
The enthalpy changes are –376 kJ mol–1 and –297 kJ mol–1 respectively.
(i) Draw a labelled enthalpy level diagram showing the relative thermodynamic stability of the Ladenburg structure, the Dewar structure and benzene.
Include the enthalpy change values in kJ mol–1 . Your diagram does not need to be to scale. (2)
(ii) Give a possible reason why the isomerisation of the Dewar structure to benzene has a lower activation energy than that of the Ladenburg structure to benzene. (1) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(f) Methylbenzene, C6H5CH3, reacts with ethanoyl chloride, CH3COCl, in the presence of the catalyst aluminium chloride, AlCl3, to form a mixture of organic products with the formula CH3COC6H4CH3. C6H5CH3 + CH3COCl → CH3COC6H4CH3 + HCl
(i) Draw the skeletal formulae of three different arenes with the formula CH3COC6H4CH3. (2)
(ii) The 13C NMR spectrum of one of these arenes, compound X, is shown.
Identify compound X. Use the number of peaks on the 13C NMR spectrum to justify your answer. (2) ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
Q11. This question is about 2-ethanoylaminobenzoic acid.
Crystals of this compound emit flashes of light when crushed. 2-ethanoylaminobenzoic acid can be synthesised using benzene as a starting material.
(i) Identify two errors in the mechanism by circling them. (2)
(ii) State how the errors identified in (a)(i) should be corrected.
Justify your answer in terms of the structures involved. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(b) Give a reason why it is important to keep the temperature below 30 °C in Step 2. (1) ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(c) State the type of reaction in Step 3. (1) .............................................................................................................................................
(d) Identify, by name or formula, the reagents needed for Step 4. (1) ............................................................................................................................................. .............................................................................................................................................
(e) Explain how the structures of ethanoyl chloride, CH3COCl, and compound A enable them to react forming 2-ethanoylaminobenzoic acid in Step 5. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(f) Calculate the volume of benzene required to form 5.92 g of 2-ethanoylaminobenzoic acid, assuming the overall yield for the synthesis is 28.2 %. Give your answer to an appropriate number of significant figures.
[Density of benzene = 0.879 g cm−3 ] (4)
(Total for question = 14 marks)
Q13. Benzene can be represented by either a cyclic triene or with a delocalised ring of electrons.
*(a) Discuss the evidence, including one example from each of spectroscopy, thermochemistry and the type of reaction normally undergone, that supports the view that the better representation of benzene is with a delocalised ring of electrons. (6)
............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(b) Benzene can be converted into phenylethanone by a Friedel-Crafts acylation.
(i) Complete the diagram, including curly arrows, to show the mechanism for this reaction. (4)
(ii) Write an equation to show how the species, CH3CO+ , could be generated. (1)
(c) Explain why phenol reacts with bromine more readily than benzene reacts with bromine. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(d) Benzene can be converted into nitrobenzene.
(i) Complete the flow diagram showing this conversion. (2)
(ii) Calculate the percentage yield if 0.642 g of nitrobenzene was made from 0.936 g of benzene.
Give your answer to an appropriate number of significant figures. (3)
(Total for question = 18 marks)
If you need the markscheme, including the examiners' reports for each question, and more exam and teaching materials on this topic, contact me through the contact page