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A LevelChemistryCIEExam Questions29. An Introduction to A Level Organic Chemistry29.2 Characteristic Organic Reactions (AL)

Characteristic Organic Reactions (AL) (CIE A Level Chemistry)

Exam Questions

37 mins4 questions
Medium
Hard
1a3 marks

This question is about benzene.

i)
Explain why the benzene molecule is planar.

[2]

ii)
Explain why all of the carbon-carbon bonds in benzene are the same length.

[1]

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1b3 marks

Benzene can be nitrated by warming it with a mixture of concentrated sulfuric acid and concentrated nitric acid.

The mechanism for the reaction is shown in Fig. 1.1.

7-1-3b-m-nitration-mechanism
Fig. 1.1


Name the type of mechanism of this nitration reaction. Explain your answer.

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1c2 marks

Benzene can be used to synthesise (4-aminophenyl)ethanoic acid which is a drug that can be used to treat chronic inflammation of the intestines.

i)
Draw the structural formula of (4-aminophenyl)ethanoic acid.

[1]

ii)
One of the intermediate products made during the synthesis of (4-aminophenyl)ethanoic acid is the molecule shown in Fig. 1.2.
7-1-3c-m-4-nitromethylbenzene-a

Fig. 1.2

Give the IUPAC name of the molecule shown in Fig. 1.2.

[1]

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1d3 marks

Noradrenaline, shown in Fig. 1.3, is a hormone and neurotransmitter which contains a benzene ring. It is released during stress to stimulate the heart and increase blood pressure.

7-1-3d-m-noradrenaline

Fig. 1.3

Other than the arene functional group, state the name of three functional groups in the noradrenaline molecule.

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2a4 marks

Benzene, C6H6, typically undergoes electrophilic substitution

i)
State the meaning of the term electrophile.
[1]
ii)
Write an equation for the reaction between benzene and concentrated nitric acid.
[1]
iii)
Identify the electrophile in the reaction and show, by means of an equation, how it is generated.
[2]

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2b5 marks

Benzene is a highly unsaturated molecule.

i)
Discuss why benzene undergoes substitution reactions rather than addition reactions.
[3]
ii)
Show, by means of an equation, the reaction of benzene with chlorine and state any necessary conditions.
[2]

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2c3 marks

An aromatic organic compound with molecular formula C7H8 reacts with bromine in the presence of UV light to produce a compound with molecular formula C7H7

i)
Name the type of reaction taking place.
[1]
ii)
Deduce the structures of the reactant and product.
[1]
iii)
Give the formula of an additional organic product that could be obtained in the reaction.
[1]

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3a1 mark

Propanal reacts with potassium cyanide, followed by dilute acid, to form the hydroxynitrile CH3CH2CH(OH)CN.

Give the IUPAC name of CH3CH2CH(OH)CN. 

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3b1 mark

Name the mechanism for the reaction between potassium cyanide and propanal.

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3c2 marks

Explain why propanal is likely to undergo this mechanism.

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1a5 marks

Under suitable conditions, 3-nitrobenzaldehyde can be formed by the reaction of benzaldehyde with appropriate reagents. 

i)
Give the mechanism, reagents and conditions for the formation of 3-nitrobenzaldehyde.
 
mechanism ................................................................................
 
reagents ................................................................................
 
conditions ................................................................................
 
[3]
 
ii)
Draw the fully displayed formula of 3-nitrobenzaldehyde highlighting the functional groups.
 
[2]

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1b3 marks

Benzaldehyde, C6H5CHO, is the simplest aromatic aldehyde with a characteristic smell of almonds or cherries.

i)
Give the bond angles within a molecule of benzaldehyde. Explain your answer.
 
[1]
 
ii)
Explain why a molecule of benzaldehyde may not be planar.
 
[2]

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1c2 marks

Benzaldehyde reacts with ethanoyl bromide in the presence of a suitable catalyst.

i)
Using the information in part (b), draw the structure of the organic product of this reaction. 
 
[1]
 
ii)
Identify the number of sigma and pi bonds in the organic product.
 
sigma bonds ..............................
 
pi bonds ..............................
 
[1]

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