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Arenes

Set BExam practice

Name

Time 1 hour

Total 20 marks

A Data Booklet may be used.

Multiple choice

4 marks

CommonWhat is the correct set of conditions for the conversion of benzene into nitrobenzene?

	acid	temperature
A	dilute HNO₃	100 °C
B	concentrated HNO₃	0 °C
C	concentrated HNO₃ and concentrated H₂SO₄	10 °C
D	concentrated HNO₃ and concentrated H₂SO₄	120 °C

Answer [1]

Source: A Level 1999 P3 Q23 (November), via EJC Arenes Topical Quiz, Q6

What is the reason for adding concentrated sulfuric acid to concentrated nitric acid in the preparation of nitrobenzene? C₆H₆(l) + HNO₃(l) → C₆H₅NO₂(l) + H₂O(l)

AIt acts as an inert solvent for the benzene and nitric acid.

BIt removes protons from nitric acid, thus forming NO₃⁻ ions.

CIt donates protons to the nitric acid, thus forming NO₂⁺ ions.

DIt removes the water, thus preventing equilibrium being established.

Answer [1]

Source: A Level 1999 P3 Q23 (June), via EJC Arenes Topical Quiz, Q7

3-chlorobenzoic acid can be synthesised from benzene in three steps. Which of the following is the best method for this synthesis?

	step 1	step 2	step 3
A	Cl₂, AlCl₃	CH₃Cl, AlCl₃	KMnO₄, H₂SO₄
B	Cl₂, AlCl₃	KMnO₄, H₂SO₄	CH₃Cl, AlCl₃
C	CH₃Cl, AlCl₃	KMnO₄, H₂SO₄	Cl₂, AlCl₃
D	CH₃Cl, AlCl₃	Cl₂, AlCl₃	KMnO₄, H₂SO₄

Answer [1]

Source: CJC 2018 Prelim P1 Q18, via EJC Arenes Topical Revision, Q5

1-(chloromethyl)-4-nitrobenzene, ClCH₂C₆H₄NO₂, can be synthesised from benzene via a 3-step synthetic method. Which of the following sequences of reactions, when carried out, gives the best yield of 1-(chloromethyl)-4-nitrobenzene?

	step 1	step 2	step 3
A	alkylation	free radical substitution	nitration
B	nitration	alkylation	free radical substitution
C	alkylation	nitration	free radical substitution
D	free radical substitution	nitration	alkylation

Answer [1]

Source: RI 2019 Prelim P1 Q17, via EJC Arenes Topical Revision, Q8

Structured questions

16 marks

CommonMethylbenzene can be used as an additive in unleaded petrol. Methylbenzene, C₆H₅CH₃, is converted into C₆H₅CO₂H by reaction I, into C₆H₅CH₂Br by reaction II, and into A by reaction III. A:

(a)

Suggest reagents and conditions for each of the reactions I, II and III, and describe as fully as you can the type of reaction undergone in each case.

[3]

(b)

There are two other positional isomers of A. Draw their structural formulae, and suggest which one is more likely to be formed along with A in reaction III.

[2]

Source: A Level 1998 P1 Q6(c), via EJC Arenes Topical Quiz, Q3(a) and (b)

B, C₈H₁₀, can react with Cl₂ in the absence of uv light and using a suitable catalyst to give dense white fumes. B can be oxidised by hot acidified KMnO₄ to form C. One mole of C is exactly neutralised by one mole of NaOH. Deduce the structures of B and C and write a balanced equation to show the oxidation of B by hot acidified KMnO₄.

[3]

Source: EJC 2022 JC1 Arenes Tutorial, Section B Q6

In Friedel–Crafts acylation, FeCl₃ is employed to attach an acyl group to an aromatic ring via electrophilic substitution. For example, compound A can be prepared by the reaction of 2-nitroanisole with ethanoyl chloride, CH₃COCl, in the presence of FeCl₃.

→

(a)

Write an equation to show how the electrophile is generated.

[1]

(b)

The Friedel–Crafts acylation of nitrobenzene by ethanoyl chloride does not take place under any conditions. Explain why nitrobenzene does not undergo acylation, but the presence of the –OCH₃ group in 2-nitroanisole permits acylation.

[2]

Source: DHS 2017 Prelim P2 Q5(a)(i) and (iii) (adapted), via EJC Arenes Topical Revision, Section B Q1

ChallengeThe table below contains information about cyclohexene and naphthalene. Cyclohexene contains one carbon–carbon double bond and shows chemical properties common to the other alkenes. Naphthalene, C₁₀H₈, shows chemical properties common to aromatic compounds.

	conditions for reaction with hydrogen	product	enthalpy change of hydrogenation / kJ mol⁻¹
cyclohexene	room temperature, nickel catalyst	cyclohexane	−118
naphthalene	–	decalin	–

(a)(i)

Calculate the enthalpy change of complete hydrogenation of naphthalene, assuming each molecule contains five C=C bonds. Use relevant enthalpy change of hydrogenation data from the table.

[1]

(ii)

The actual value for the enthalpy change of complete hydrogenation of naphthalene is −335 kJ mol⁻¹. Compare the value calculated in (a)(i) with this, and suggest what this indicates about the stability of the molecule.

[1]

(iii)

Describe the hybridisation of the orbitals in, and the bonds between, the carbon atoms within a naphthalene molecule, suggested by your answers in (a)(i) and (a)(ii).

[2]

(b)

Suggest the reagents and conditions needed to ensure that complete hydrogenation of naphthalene occurs.

[1]

Source: A Level 2017 P3 Q7 (modified), via EJC 2022 JC1 Arenes Tutorial, Section B Q1