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A LevelChemistryCIEExam Questions30. Hydrocarbons (AL)30.1 Arenes

Arenes (CIE A Level Chemistry)

Exam Questions

2 hours11 questions
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Hard
1a1 mark

Benzene can react with aluminium bromide, AlBr3, and bromoethane, CH3CH2Br, to form ethylbenzene.

Write the equation for the formation of the CH3CH2+ species. 

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1b1 mark

Name the mechanism for the formation of ethylbenzene from benzene and aluminium bromide.

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1c3 marks

Using the CH3CH2+ electrophile, draw the mechanism for the conversion of benzene into ethylbenzene. Include all necessary curly arrows and charges.

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1d1 mark

State the type of reaction that occurs in part (c).

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2a2 marks

Benzene undergoes substitution reactions. State the equation for the reaction of benzene with nitric acid to produce nitrobenzene and water.

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2b2 marks

The structure of methylbenzene is shown below in Fig. 2.1.

a2c33069-43fc-46b0-af04-465fc1e6e6d1
Fig. 2.1

Draw the structures of the two isomers of choromethylbenzene formed from the reaction of methyl benzene and Cl2 in the presence of AlCl3. 

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2c1 mark

State the type of reaction that benzene will typically undergo.

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3a1 mark

This question is about the bromination of benzene.

State the name of the mechanism that benzene will undergo if reacted with bromine in the presence of a halogen carrier to form bromobenzene, C6H5Br. 

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3b2 marks

Write an equation to show how the halogen carrier generates the Br+ ion in order to allow the reaction in part (a) to occur. 

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3c3 marks

Complete the mechanism in Fig. 3.1 for the formation of bromobenzene. Include relevant charges where appropriate. 

6-1_q2c-ocr-a-as--a-level-easy-sq
Fig. 3.1

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4a1 mark

This question is about the reactions of methylbenzene.

Draw the structure of compound A in Fig. 4.1.


7-2-3a-e-compound-a-cie-7-2-q3-a
Fig. 4.1

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4b1 mark

Draw the structure of compound B in Fig. 4.2.

7-2-3b-e-compound-b-cie-7-2-q3-a
Fig. 4.2

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4c3 marks

State the reagents and conditions required for reaction 1 in Fig. 4.3 for the formation of benzoic acid from methylbenzene.

7-2-3c-e-benzoic-acid-cie-7-2-q3
Fig. 4.3

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1a5 marks

4-nitromethylbenzene can be prepared via an electrophilic substitution reaction as shown in Fig. 1.1.

fig-4-1-9701-y22-sp-4-cie-ial-chem
Fig. 1.1

i)

This reaction also forms an isomer of 4-nitromethylbenzene as a by-product. Draw the structure of this by-product.

[1]

ii)
Write an equation for the reaction between HNO3 and H2SO4 that forms the electrophile for this reaction.

 [1]

iii)
Describe how the structure and bonding of the six-membered ring in intermediate T differ from those in methylbenzene. In your answer refer to the hybridisation, the π bonding and the bond angles in the ring system.
[3]

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1b6 marks

Benzocaine is used as a local anaesthetic. It can be synthesised from 4-nitromethylbenzene by the route shown in Fig. 1.2.

fig-4-2-9701-y22-sp-4-cie-ial-chem

Fig. 1.2

i)
 Give the systematic name of compound W.

[1]

ii)
Suggest the reagents and conditions for step 1.

step 1 .....................................................................................

[2]

ii)
Suggest the reagent for step 2.

step 2 ...................................................................................................

[1]

iii)
Suggest the reagents and conditions for step 3 and step 4.

step 3 ........................................................................................................

step 4 ........................................................................................................

[2]

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1c5 marks

A sample of benzocaine was analysed by carbon-13 NMR and proton NMR spectroscopy.

i)
Predict the number of peaks in the carbon-13 NMR spectrum of benzocaine.

[1]

Benzocaine was dissolved in CDCl3 and the proton NMR spectrum of this solution was recorded as shown in Fig. 1.3.

fig-4-3-9701-y22-sp-4-cie-ial-chem

Fig. 1.3

ii)
The data in Table 1.2 should be used in answering this question.
Complete Table 1.1 for the chemical shifts δ 1.2 ppm, 3.5 ppm and 5.5 ppm.

Table 1.1

δ / ppm environment of proton number of 1H atoms responsible for the peak splitting pattern
1.2      
3.5      
5.5      
7.1–7.4 attached to aromatic ring 4 two doublets

[3]

iii)
Explain the splitting pattern for the absorption at δ 1.2 ppm.

[1]

Table 1.2
Environment of proton Example chemcial shift
range, δ / ppm
alkane –CH3, –CH2–, >CH– 0.9–1.7
alkyl next to C=O CH3–C=O,–CH2–C=O,
>CH–C=O		 2.2–3.0
alkyl next to aromatic ring CH3–Ar, –CH2–Ar,
>CH–Ar		 2.3–3.0
alkyl next to electronegative atom CH3–O,–CH2–O,
–CH2–Cl		 3.2–4.0
attached to alkene =CHR 4.5–6.0
attached to aromatic ring H–Ar 6.0–9.0
aldehyde HCOR 9.3–10.5
alcohol ROH 0.5–6.0
phenol Ar–OH 4.5–7.0
carboxylic acid RCOOH 9.0–13.0
alkyl amine R–NH– 1.0–5.0
aryl amine Ar–NH2 3.0–6.0
amide RCONHR 5.0–12.0

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1d3 marks

Benzocaine can also be used to synthesise the azo compound S by the following route.


fig-4-4-9701-y22-sp-4-cie-ial-chem


Fig. 1.4

i)
Suggest the reagent(s) used for step 1.


 [1]

ii)
Suggest structures for compounds R and S and draw them in the boxes in Fig. 1.4.

[2]

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2a4 marks

Benzene can undergo electrophilic substitution with ethanoyl chloride in the presence of aluminium chloride.

i)
Write an equation to show the formation of the electrophile.
[1]
ii)
Draw the mechanism for the reaction.
[3]

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2b2 marks

The organic product from part (a) can be reduced to form an alcohol.

Name a suitable reducing agent and write a chemical equation to show this reduction, using [H] to represent the reducing agent.

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2c2 marks

Outline the mechanism for the reaction of the ethanoyl chloride with aluminium chloride to form the acylium ion needed for electrophilic substitution.

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2d2 marks

Explain how the catalyst reforms.

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3a4 marks

Compound A can be formed from ethylbenzene by the following route in Fig. 3.1.

7-2-3a-m-fig--3-1-7-2m-q3

Fig. 3.1 

Suggest reagents and conditions for the following steps.

Step 1 ......................................................................................................

Step 2 .......................................................................................................

Step 3 .......................................................................................................

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3b2 marks

Suggest the structures of the organic products of the reactions between each of the compound A and the following reagents. If no reaction occurs write ‘no reaction’.

Reagent  Product with compound A
Na








H+ / KMnO4







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3c1 mark

Explain why ethyl-2-nitrobenzene is formed rather than ethyl-3-nitrobenzene.

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3d1 mark

Using your answer to (a), write the equation for the formation of the electrophile in step 1.

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4a2 marks

Methylbenzene can undergo different reactions to form the products shown in Fig. 4.1.

BMr5iAaI_7-2-4a-m-fig--4-1-reactions-of-methylbenzene

Fig. 4.1

Give the reagents and conditions for these two reactions.


reaction 1 ........................................................................................

reaction 2 ........................................................................................

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4b2 marks
i)
Name the mechanism of reaction 1 in part (a)

[1]
ii)
Draw the structure of the product obtained if reaction 1 is carried out using an excess of bromine.

[1]

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4c3 marks

Draw the reaction mechanism for reaction 2.

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4d2 marks

Nitrobenzene reacts in the same conditions as reaction 2 in part (a). Draw and name the product of this reaction.

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1a3 marks

The nitration of benzene is the first important step in manufacturing dyes and explosives. 

i)
Write the equation for the generation of the electrophile.
 
[1]
 
ii)
State which reactant acting as a Brønsted-Lowry base and justify your answer.
 
[1]
 
iii)
Identify the conjugate acid in the reaction.
 
[1]

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1b5 marks

Compound B is produced in two steps as outlined in Fig. 1.1.

7-2-1b-h-benzene-pathway-1 

Fig. 1.1

i)
Outline the reagents and conditions required for the production of compound A drawn in Fig. 1.1.
 
[2]
 
ii)
Using curly arrows, describe the mechanism for step 1.
 
[3]

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1c2 marks

Draw the dot-and-cross diagram for the structure of the catalyst, once the electrophile has been generated in part (b).

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1d4 marks

Explain why benzene can generally only undergo substitution reactions.

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2a2 marks

Fig. 2.1 shows the formation of a ketone followed by an alcohol. 

7-2-2a-h-benzene-to-ketone-to-alcohol-1

Fig. 2.1

Draw the mechanism to show the formation of the catalyst responsible for step 1.

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2b5 marks

Draw the mechanism for the formation of the ketone, including the regeneration of the catalyst required.

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2c2 marks

State the reagents required for step 2.

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3a4 marks

Benzene can be converted into cyclohexane as shown in Fig. 3.1.

7-2-3a-h--benzene-to-cyclohexane

Fig. 3.1

i)
For this reaction, name the type of reaction and identify the reagent and conditions needed.
 
type of reaction ................................................................................
 
reagent and conditions ................................................................................
 
[2]
 
ii)
State the bond angles in benzene and cyclohexane.
 
bond angle in benzene ..............................
 
bond angle in cyclohexane ..............................
 
Explain your answers.
 
[2]

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3b4 marks

When benzene reacts with SO3, as shown in Fig. 3.2, benzenesulfonic acid is produced.

7-2-3b-h-fig--3-2-benzenesulfonic-acid-fig--3-3-benzenesulfonic-acid-1

Fig. 3.2

The mechanism of this reaction is similar to that of the nitration of benzene. Concentrated H2SO4 is used in an initial step to generate the SO3H+ electrophile as shown.

SO3 + H2SO4 → SO3H+ + HSO4– 

i)
Draw a mechanism for the reaction of benzene with SO3H+ ions in Fig. 3.3. Include all necessary curly arrows and charges.
 
7-2-3b-h-fig--3-2-benzenesulfonic-acid-fig--3-3-benzenesulfonic-acid-2
 
Fig. 3.3
 
[3]
 
ii)
Write an equation to show how the H2SO4 catalyst is reformed.
 
[1]

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3c5 marks

3-aminobenzoic acid can be synthesised from methylbenzene in three steps as shown in Fig. 3.4.

7-3-3c-h-fig--3-4-pathway

Fig. 3.4

i)
Draw the structures of M and N in the boxes.
 
[2]
 
ii)
Suggest reagents and conditions for each step of the synthesis.
 
step 1 ................................................................................
 
step 2 ................................................................................
 
step 3 ................................................................................
 
[3]

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