5.3 ARENES

Section A

For each of the questions only one of the lettered responses (A-D) is correct.

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet.

1. Which one of the following statements is untrue regarding methyl-3 nitrobenzoate?

A It may be prepared by the nitration of methyl benzoate.

B It may be prepared by a reaction involving electrophilic substitution.

C It is isomeric with methyl 2-nitrobenzoate.

D Its preparation must be carried out above 100 ^oC.

Section B

Answer all questions in the spaces provided

1. In the 1970s bromine was produced largely from the electrolysis of sea water. Bromine reacts with both ethene and benzene. Most of it was converted into 1,2-dibromoethane by reaction between ethene and bromine. The 1,2-dibromoethane was used as a scavenger for lead in petrol.

(a)

(i) Write a structural equation for the reaction between ethene and bromine.

[2]

(ii) Write an equation for the reaction between benzene and bromine, naming the catalyst.

[3]

(iii) Contrast the reaction of ethene and bromine with that of benzene and bromine with reference to bond type and bond enthalpy.

[4]

(b) Explain why the combustion of modern hydrocarbon fuels leads to one major environmental problem.

[2]

16 Benzene was discovered by Michael Faraday and its cyclic structure was deduced by August Kekul@. The accepted structure today involves delocalised electrons.

Kekul6 structure Delocalised structure

(a) Draw two structures for benzene showing the p-orbitals before and after delocalisation.

[2]

(h) Nitration of benzene can be achieved using a mixture of concentrated nitric and sulphuric acids.

(i) Write an equation to show how these two acids react together.

[2]

(ii) Name the ion, produced in this reaction, which attacks the benzene molecule.

(iii) Using a flow scheme, describe the mechanism of the nitration of benzene.

[31

(iv) What is the name given to this type of mechanism?

- [21

(v) If 20 cm3 of benzene (density 0. 87 g cm-3) is converted to nitrobenzene and a pure sample of 6.5 g of nitrobenzene obtained, calculate the percentage yield.

[3]

(vi) Benzene and nitrobenzene are extremely toxic. A safer illustration of nitration can be carried out using the mixture of the two acids and methyl benzoate. Describe the preparation of a pure sample of the product of this reaction. (Up to twomarks may be obtained for the quality of language in this part.)

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