CIE A Level Chemistry

Topic Questions

A LevelChemistryCIETopic Questions7. Organic Chemistry (A Level Only)7.3 Halogen Compounds (A Level Only)

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First teaching 2020

Last exams 2024

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7.3 Halogen Compounds (A Level Only)

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1a2 marks

At room temperature and pressure, bromine reacts with benzene, in the presence of a halogen carrier to produce bromobenzene. This is an electrophilic substitution reaction.

The electrophile is the bromonium ion, Br+ and is generated when bromine reacts with the halogen carrier, e.g. AlBr3.

Complete the mechanism in Fig. 1.1 to show how the bromonium ion is produced by adding any full and partial charges and curly arrows.

7-3-1a-e-formation-of-bromonium-ion-a

Fig. 1.1

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1b3 marks

Complete the mechanism in Fig. 1.2 to show how bromobenzene is produced from Br+ and benzene. Include any relevant charges and curly arrows.

7-3-1b-e-bromobenzene-mechanism-a

Fig. 1.2

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1c1 mark

Write an equation to show the regeneration of the catalyst.

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2a2 marks

Methylbenzene can react with chlorine under different conditions to give the monochloro derivatives F and G. shown in Fig. 2.1.

7-3-2a-e-monochloro-products

Fig. 2.1

Suggest reagents and conditions for each reaction.

reaction 1 ..........................................................................................
reaction 2 ..........................................................................................

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2b2 marks

Identify the type of reaction mechanism that occurs in each reaction in Fig. 2.1.

reaction 1 ..........................................................................................
reaction 2 ..........................................................................................

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2c2 marks

When the reagent used in reaction 1 is present in excess, further organic products are formed. 

Draw the structure of one of these organic products and give its name.

Structure  
Name ..........................................................................

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3a1 mark

2-bromopentane is a halogenoalkane and bromobenzene is a halogenoarene.

State which is the most reactive compound.

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3b1 mark

The average bond enthalpy of a C–Br bond is 276 kJ mol-1. Suggest whether the bond enthalpy of the C–Br bond in bromobenzene is greater or less than the average bond enthalpy and state what this means about the strength of the C–Br bond in bromobenzene.

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3c1 mark

2-bromopentane readily undergoes nucleophilic substitution with a hydroxide ion, OH–, to form pentan-2-ol whereas bromobenzene requires extreme conditions to react when attacked by a nucleophile, such as OH–.

Suggest what happens, under standard conditions, as a hydroxide ion approaches a molecule of bromobenzene.

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1a5 marks

Nitration of a benzene ring forms nitrobenzene. The subsequent reactions of nitrobenzene are shown in Fig. 1.1.

52e8e77b-9464-48b8-87b0-b5e91f3646ab

Fig. 1.1

The structures of the products have the same molecular formula. Explain why these products are different. In your answer include the structures of compounds X and Y and reagents for reactions A and B. 

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1b3 marks

Using curly arrows, describe the mechanism for reaction A. 

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1c2 marks

State the IUPAC name of Compound Z and draw the structure.

f365e2ec-eaee-4151-b144-0d222316c4f6

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2a4 marks

Chlorobenzene is formed by bubbling chlorine gas into benzene at room temperature in the presence of anhydrous AlCl3.

Explain, by the use of equations, how AlCl3 acts as a catalyst in the chlorination of benzene.

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2b1 mark

Nitrobenzene undergoes further substitution considerably more slowly than chlorobenzene. In nitrobenzene, the incoming group joins the benzene ring in the 3-position, whereas in chlorobenzene the incoming group joins to the benzene ring in the 4-position. 

Use these ideas to suggest the structures of the intermediate compounds Y and Z in the following synthesis of 4-chlorophenylamine.

synthesis-4-chlorophenylamine

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2c1 mark

Suggest the structure of the organic product formed when 4-chlorophenylamine reacts with bromine water.

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3a2 marks

Fig. 3.1 shows two reactions of methyl benzene.

7-3-3a-h-cie-chloro-1

Fig. 3.1 

i)
State the conditions required for reaction 1.
 
[1]
 
ii)
State the conditions required for reaction 2.
 
[1]

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3b1 mark

State the reagent needed to carry out the following reaction occurring in Fig. 3.2. 

7-3-3b-h

Fig. 3.2 

   reagent for reaction 3 ..............................................................

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3c3 marks

The three chloro-compounds A, B and C vary in their ease of hydrolysis.

i)
Place a tick in the box in Table 3.1 corresponding to the correct relative rates of hydrolysis. [the symbol ‘>’ means ‘faster than’].

Table 3.1

  Place one tick only in this column
A > B > C  
A > C > B  
B > A > C  
B > C > A  
C > B > A  
C > A > B  
[1]
ii)
Suggest an explanation for these differences in reactivity
[2]

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1a2 marks

This question is about halogenoarene compounds.

State the reagents and name of the mechanism used to convert benzene into chlorobenzene

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1b1 mark

Using your answer to (a), write the equation for the generation of the ion which reacts with benzene. 

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1c4 marks

Draw the mechanism for the chlorination of benzene.

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1d3 marks

Explain how the carbon - chlorine bond in chlorobenzene prevents nucleophilic substitution from occurring.

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2a4 marks

Predict the products of the following reactions in Fig. 2.1 and draw their structures in the boxes provided. Note that the molecular formula of the final product is given in each case.

7-3-2a-m-cie-ial-7-3-m-fig-2-1--question-a

Fig. 2.1

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2b1 mark

Write the equation for the generation of the electrophile when methylbenzene reacts with bromine and aluminium bromide.

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2c3 marks

Draw the reaction mechanism for the reaction of methylbenzene with bromine and aluminium bromide.

[4]

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2d4 marks

Explain why halogenoalkanes such as bromopropane are more reactive than halogenoarenes such as bromobenzene.

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3a2 marks

A student investigated two reactions of phenylethene, C6H5CHCH2 as shown in Fig. 3.1. First she reacted phenylethene with excess bromine at room temperature to form Compound A. She then added aluminium bromide, AlBr3 to the reaction mixture to form Compound B.

7-3-3a-m-reactions-of-phenylethene-fig-3-1-a

Fig. 3.1

Draw the structures of Compound A and B. 

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3b4 marks

Name and outline the mechanism for the formation of Compound B from Compound A.

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3c2 marks

Nitrobenzene was reacted with aluminium chloride and chlorine. Name and draw the structure of the aromatic product formed in this reaction.

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