12 Arenes – aromatic hydrocarbons
Extension questions
Topic 12 Extension questions
1 Benzene reacts with bromomethane, CH3Br, to give methylbenzene, C6H5CH3. The reaction involves
electrophilic substitution.
a) Explain the term electrophilic substitution.
b) What catalyst could be used for the reaction?
c) Outline a mechanism for the reaction, including curly arrows and relevant dipoles. Include also the step that
forms the attacking electrophile.
d) Explain in terms of structure and bonding why benzene and ethene react differently with electrophiles.
2 The drug L-dopa is used in the treatment of Parkinson’s disease. Its structural formula is:
a) Write the structural formulae of the sodium salts formed when L-dopa reacts with
i) excess sodium hydroxide solution
ii) excess sodium carbonate solution.
b) Predict the structural formula of the organic ion produced when L-dopa reacts with excess dilute
hydrochloric acid.
c) The benzene ring in L-dopa is more reactive with electrophiles than that in benzene.
i) Why is the benzene ring in L-dopa more susceptible to attack by electrophiles than benzene itself?
ii) Write the structural formula of one possible monochloro-product when chlorine reacts with L-dopa.
d) In the human body, an enzyme called L-dopa decarboxylase eliminates the carboxylic acid group from
L-dopa to produce the primary amine, dopamine.
i) What is a primary amine?
ii) Draw the structural formula of dopamine.
3 Benzene is one of the most important
aromatic compounds in industry. The
flow chart on the right shows the
formation of three useful products from
benzene.
Name substances A to F.
Reactions to form D and nitrobenzene involve electrophilic substitution.
i) Write the formula of the electrophile in each case.
ii) Suggest one use for the compounds formed by the nitration of arenes.
c) i) Suggest the conditions used to produce A from benzene.
ii) Suggest a possible use for A.
d) Substance D can be dehydrogenated to form phenylethene (styrene) which is used to manufacture
poly(phenylethene).
i) Write an equation for the formation of poly(phenylethene) from phenylethene.
ii) What type of reagent is needed to start the formation of poly(phenylethene)?
iii) State one use of poly(phenylethene).
a)
b)
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© G. Hill and A. Hunt 2009 Edexcel Chemistry for A2