AQA A Level Chemistry

Topic Questions

7.4 Aromatic Chemistry (A-level only)

1a3 marks

Name the following aromatic compounds shown in Figure 1 

Figure 1

1-6

1b1 mark

Name the type of mechanism that benzene will undergo, in order to form compound shown in Figure 1 of part (a).

1c2 marks

State the reagents required for the following reactions:

i)
C6H6 to C6H5NO2

ii)
C6H5NO2 to C6H5NH2
1d3 marks

Outline the mechanism for the formation of Compound B from benzene.

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2a1 mark

Name the aromatic compound in Figure 1. 

Figure 1

2-5

2b3 marks

A student wrote the following paragraph about the structure of benzene.

‘Each carbon atom in the ring forms three pi bonds using the sp3 orbitals. The remaining p orbitals overlap laterally with p orbitals of neighbouring carbon atoms. The sideways overlap of p orbitals results in the electrons being centred on each carbon atom in the benzene ring.

Identify and correct the three mistakes the student has made.

2c1 mark

State the bond angle that is present in the benzene molecule.

2d2 marks

Cyclohexene is an unsaturated hydrocarbon and can undergo hydrogenation as shown in Figure 1.

Figure 1

 

3-6

When benzene undergoes the same reaction with three hydrogen molecules the expected enthalpy change of the reaction is lower than expected.

i)
State the expected value of the hydrogenation of benzene.

ii)
Explain why the enthalpy value for the hydrogenation of benzene is lower than expected.

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3a2 marks

Ethylbenzene can be formed from benzene via Friedel-Crafts alkylation.

Write an equation for the formation of the electrophile that is required for this reaction.

3b1 mark

Draw the structure of ethylbenzene produced in this reaction.

3c3 marks

Outline the mechanism for the production of ethylbenzene from benzene.

3d2 marks

Write an equation to show how the catalyst for this reaction is regenerated.

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4a2 marks

The production of phenylethanone, shown in Figure 1, is produced from the reaction between an acid chloride and benzene in the presence of aluminium chloride.

 Figure 1

4-6

 

 

Write an equation for the generation of the electrophile required for this reaction.

4b2 marks

Explain why the species generated in the reaction in your answer to part (a) is classed as an electrophile.

4c1 mark

Identify the class of compound to which phenylethanone belongs.

4d1 mark

Ethylbenzene can be formed when ​​benzene is treated with a mixture of ethene, hydrogen chloride, HCl and aluminium chloride, AlCl3. 

Write an equation to show the generation of the electrophile in this reaction. 

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5a1 mark

Benzene can undergo multiple electrophilic substitution and form 2,4,6-trinitrotoluene can be formed from benzene. Draw the structure of 2,4,6-trinitrotoluene.

5b4 marks

The first step in this process is to form methyl benzene, commonly known as toluene from benzene.

Bromomethane, CH3Br in the presence of aluminium bromide, AlBr3, is used Outline the formation of the electrophile and the mechanism for this reaction.

5c2 marks

Explain why methylbenzene is more reactive than benzene

5d2 marks

Write two equations to show the generation of the nitronium ion

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1a5 marks

Benzene is an important industrial chemical used in a variety of manufacturing processes. Cyclohexane is a cyclic hydrocarbon with the formula C6H12

i)
Outline a reaction for the conversion of benzene into cyclohexane and include suitable reagents and conditions for this reaction. 

ii)
In 1885 Kekule proposed a model for the structure and bonding for benzene, however there is evidence to suggest that this model may not be correct and there are alternative structures for benzene proposed. Explain why scientists doubted Kekule’s structure.
1b4 marks

Two different structures when representing benzene are often shown in textbooks, both of which are shown in Figure 1.

Figure 1

1-8

 By using diagrams to help, describe the difference in orbital overlap the difference in bonding structures X and Y represent.

1c3 marks

The theoretical molecule cyclohexa-1,3,5-triene reacts differently with bromine than 

i)
Benzene will react with bromine in the presence of aluminium bromide. Draw the products of this reaction.

ii)
Draw the products produced from the reaction of cyclohexa-1,3,5-triene with bromine.

 

1d2 marks

Draw a diagram to show the resonance structure in a molecule of benzene.

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2a3 marks

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

i)
Outline the generation of the electrophile for the nitration of benzene by writing an equation.

ii)
Indicate in your equation which reactant is acting as a Brønsted Lowry base. 
Explain your answer and identify the conjugate acid and base pairs in the reaction. 
2b5 marks

Compound B is produced in two steps. 

Figure 1

2-7 

i)
Outline the reagents and conditions required in for the production of Compound A drawn in Figure 1.

ii)
Outline the mechanism for step 1.
2c2 marks

Draw a Lewis structure for the structure of the catalyst once the electrophile has been generated. 

2d4 marks

Explain why benzene can only undergo substitution reactions.

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3a2 marks

Benzene undergoes a substitution reaction to form compound X. Give the formulas of the reagents required for this conversion in the presence of a catalyst.

Figure 1

3-7

3b4 marks

Outline the mechanism for compound X for the substitution of a nitronium ion onto the benzene ring.

3c5 marks

N-phenylethanamide can be produced in two steps from nitrobenzene.
Give the reagents required for both steps and draw the structures for the compounds formed.

3d2 marks

State the name of the mechanism required for the second step of the reaction and describe the first step of the mechanism to produce the intermediate.  

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4a3 marks

Propene will react with benzene in the presence of aluminium chloride and hydrogen chloride.

Outline the mechanism that occurs in order to generate the positively charged carbon species in this reaction. 

4b4 marks

Outline the mechanism for the formation of the final products for the reaction outlined in part (a).

4c1 mark

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

4d2 marks

Explain why a molecule of benzene won’t tend to react with ammonia to form phenylamine.  

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5a3 marks

The energy change for hydrogenation of cyclohexene is -120 kJ mol-1. However, when benzene undergoes hydrogenation, the energy change is 152 kJ mol-1 less than expected. 

Use this data to explain the relative stabilities of benzene and the theoretical cyclohexa-1,3,5-triene molecule.

5b3 marks

When cyclohexa-1,3-diene undergoes hydrogenation it will have a different value than expected. 

Using the data given in part (a) explain why cyclohexa-1,3-diene has a different value than expected and suggest a value for the energy change for this reaction. 

5c2 marks

Explain why the energy change for the hydrogenation of cyclohexa-1,4-diene will be different from the value for the hydrogenation of cyclohexa-1,3-diene.

5d4 marks

Ibuprofen is an anti-inflammatory drug that is readily available. Its structure is shown in Figure 1.

Identify both an sp2 and sp3 hybridised carbon atoms present in the ibuprofen structure. 
Justify your answer. 

Figure 1

4-7

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1a4 marks

Describe the structure of cyclohexene. Explain why the molecule is not planar. Your answer should include any necessary bond angles.

1b3 marks

The following information is known about the hydrogenation of cyclohexene: 

   cyclohexene + hydrogen → cyclohexane                  ΔHΘ = -120 kJ mol-1 

Use this data to predict a value for the hydrogenation of the theoretical compound, cyclohexa-1,3,5-triene. 

State and explain the stability of benzene compared to the theoretical cyclohexa-1,3,5-triene compound.

1c6 marks

Many compounds in Chemistry contain delocalised electrons.

Use your knowledge of structure and bonding to explain which of the following compounds does not contain delocalised electrons:

  • Graphite
  • Poly(propene)
  • Sodium
1d5 marks

Benzene and three of its chemical derivatives, chlorobenzene, methylbenzene and phenol, are aromatic compounds which have a variety of industrial applications. 

Benzene is mainly used in the manufacture of other more complex chemicals, such as ethylbenzene and cumene. Billions of kilograms of ethylbenzene and cumene are produced annually.

Like benzene, chlorobenzene is used to make several other chemicals. It is also used to degrease car parts and in some pesticide formulations. 

In industry, methylbenzene is known by its common name, toluene. It is used as a solvent in paint thinner, permanent markers, contact cement and glue.

Phenol is a benzene ring with an -OH group attached in place of one of the hydrogen atoms, and its chemical derivatives are used in the manufacture of various plastics, nylon, detergents, herbicides and various pharmaceutical drugs.

Compare the relative reactivities of benzene, chlorobenzene, methylbenzene and phenol in terms of electrophilic substitution reactions. 

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2a5 marks

Benzene can undergo electrophilic substitution with ethanoyl chloride in the presence of a suitable catalyst.

Name the catalyst and write an equation to show the formation of the electrophile.

Outline the mechanism for this reaction

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.

2c2 marks

The alcohol produced in part (b) is a mixture of isomers.

Draw the 3-dimensional representation of these isomers. Assuming that a single pure isomer was produced, describe a test which could be used to prove that the product was pure.

2d3 marks

Propanoyl chloride can be reacted with the alcohol formed in part (b) to produce an ester.

Explain the expected observations during the reaction and draw the ester produced.

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3a2 marks

Ethylbenzene, C6H5CH2CH3, is an important chemical intermediate in the manufacture of polystyrene, pesticides, rubber, paint and inks.

The synthesis of ethylbenzene can occur via Friedel-Crafts alkylation using ethene, hydrogen chloride, benzene and an aluminium chloride, AlCl3, catalyst.

Name the mechanism for the reaction of ethene and hydrogen chloride.

Write an equation for the subsequent formation of the carbocation that reacts with benzene to produce ethylbenzene.

3b3 marks

Outline the mechanism for the reaction of benzene with the carbocation that was formed in part (a).

3c2 marks

Ethylbenzene can also be formed by reacting ethanoyl chloride with benzene, in the presence of an AlCl3 catalyst.

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

3d2 marks

Aluminium chloride is used as the catalyst in the reaction between benzene and ethanoyl chloride.

Explain how the catalyst reforms.

 

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4a5 marks

Paracetamol is a common painkiller that is often manufactured in a multi-step process using 4-aminophenol. Phenol is a common organic chemical, comprised of a benzene ring with one hydroxyl group attached.    

Suggest a two-step synthetic route to form 4-aminophenol from phenol. 

Step 1 of your route should include reagents, conditions, equations to form the electrophile and the identity of the product.

Step 2 of your synthetic route should include the reagents to form 4-aminophenol from your Step 1 product.

4b3 marks

The uncontrolled nitration of phenol can lead to the formation of 2,4,6-trinitrophenol, commonly known as picric acid.

This reaction would require formation of a dinitrophenol intermediate. Draw the possible isomers of this intermediate and name the type of isomerism displayed.

4c4 marks

Paracetamol, figure 1, can be manufactured by the reaction of 4-aminophenol with ethanoyl chloride.

Figure 1

9-3

Name and outline the mechanism for this reaction.

4d3 marks

A student started with 3.96 g of ethanoyl chloride (Mr = 78.5).

After preparation of impure paracetamol followed by recrystallisation, the student actually obtained 6.11 g of pure paracetamol (Mr = 151).

Calculate the percentage yield of pure paracetamol from this experiment.

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5a3 marks

2,4,6-trinitrotoluene (TNT) can be manufactured from benzene as shown in Figure 1.

Figure 1

11-1

Step 1 involves the Friedel-Crafts alkylation of benzene to produce methylbenzene, commonly known as toluene.

Calculate the percentage atom economy for Step 1.

5b3 marks

Step 2 of Figure 1 involves the formation of a nitronium ion for the nitration of Toluene, as shown in the following equation: 

HNO3 + 2H2SO4 → NO2+ + 2HSO4- + H3O+ 

i)
Explain the role of the nitric acid in the formation of the electrophile.

ii)
Explain the role of the sulphuric acid in the overall nitration reaction.
5c3 marks

Outline the mechanism, show in Step 2 of Figure 1, for the formation of 4-nitrotoluene (Compound A) from toluene.

5d3 marks

The nitration steps can be hard to control and lead to the runaway formation of 2,4,6-trinitrotoluene, otherwise known as TNT.

A sample was taken during the nitration steps. Analysis of the sample showed the compound to have 7 peaks on its 13C-NMR spectrum.

State which of the nitro compounds, A, B or C, is in the sample tested. Justify your answer. 

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