A LevelChemistryOCRExam Questions6. Organic Chemistry & AnalysisBenzene & Aromatic Compounds

Benzene & Aromatic Compounds (OCR A Level Chemistry A): Exam Questions

Exam code: H432

3 hours31 questions

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Benzene & Aromatic Compounds

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1
1 mark

What reagents are required for the conversion of benzene to nitrobenzene?

  • Hydrogen gas in presence of nickel catalyst

  • Concentrated nitric acid and concentrated hydrochloric acid

  • Concentrated sulfuric acid and concentrated nitric acid

  • Tin with concentrated hydrochloric acid

Choose your answer

2
1 mark

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

Chemical reaction showing cyclohexene with hydrogen forming cyclohexane, with an enthalpy change of -120 kJ mol⁻¹.

The expected enthalpy change for the hydrogenation of benzene is −360 kJ mol−1. The actual value is −208 kJ mol−1.

Which statement correctly explains this difference?

  • The s orbitals overlap to produce a stable structure

  • The bond length of the C=C bonds are shorter than the C-C bonds

  • Delocalisation of electrons in the benzene ring increases the stability

  • Each carbon in benzene has three covalent bonds

Choose your answer

3
1 mark

Which product is formed when benzene, C6H6, reacts with ethanoyl chloride, CH3COCl, in the presence of aluminium chloride, AlCl3?

  • C6H6COCH3

  • HCl

  • C6H5CH3CO

  • C6H5CH2CH3

Choose your answer

4
1 mark

Which statement about phenol is not correct? 

  • Phenol behaves as a weak acid 

  • Phenol reacts with bromine to form an orange precipitate 

  • The formula for the phenoxide ion is C6H5O-

  • Phenol reacts with sodium to form hydrogen gas

Choose your answer

5
1 mark

Which part of the following mechanism is not correct?

Chemical reaction mechanism (with a deliberate error) showing benzene undergoing electrophilic substitution by NO2, to form nitrobenzene.

How did you do?

1
1 mark

Which statement explains why the enthalpy of hydrogenation of benzene is lower than expected?

  • The overlap of p-orbitals allows electrons to become delocalised

  • Benzene contains both single and double bonds

  • The carbon-carbon bond lengths in benzene are shorter than a carbon-carbon single bond

  • Benzene contains sp2 hybridised carbon atoms

Choose your answer

2
1 mark

Benzene can undergo nitration to form nitrobenzene.

Which statement about this reaction is not correct?

  • Concentrated nitric acid acts as a base

  • A nitronium ion acts as an electrophile

  • HSO4- is produced in the formation of the electrophile

  • Aluminum chloride is required as a catalyst for the reaction

Choose your answer

3
1 mark

Which statement about the reactions of benzene is correct?

  1. The delocalised system in benzene will repel attack from a nucleophile

  2. During electrophilic substitution, the electrophile attacks the delocalised electrons in the benzene ring

  3. NH3 is not a strong enough nucleophile to undergo nucleophilic substitution with benzene

  • 1, 2, and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

Choose your answer

4
1 mark

The following compound can be synthesised from benzene. 

Chemical structure of phenylpropanone.

Which reagent is required for this conversion?

  • CH3CH2COOH

  • CH3CH2CH2Cl

  • CH3CH2COCl 

  • CH3CH2CHO

Choose your answer

5
1 mark

Which of the following can react with propanoic acid and with phenol?

  • Bromine

  • Ethanol and concentrated sulfuric acid

  • Sodium hydrogen carbonate 

  • Aqueous sodium hydroxide 

Choose your answer

1
1 mark

Which statement(s) provide evidence for the modern delocalised model of benzene rather than the Kekulé model?

  1. The enthalpy change of hydrogenation of benzene is less exothermic than the theoretical value for ‘cyclohexatriene’.

  2. All carbon–carbon bond lengths in benzene are identical and intermediate in length between a C–C single bond and a C=C double bond.

  3. Benzene is a planar molecule with C–C–C bond angles of 120°.

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

Choose your answer

2
1 mark

Which statement is not correct?

  • Nitrobenzene has reduced electron density so is less reactive than benzene. 

  • Increased electron density at positions 2, 4 and 6 of aminobenzene promotes substitution at these positions. 

  • The −NO2 group in nitrobenzene withdraws electron density predominantly from positions 3 and 5.

  • Phenol is more reactive than benzene and is a weak acid. 

Choose your answer

3
1 mark

A multi-step mechanism is shown below.

Chemical reaction diagram showing four steps between benzene derivatives with methyl, nitro, amino, chloromethyl, and acetyl groups.

Which of the following reagents is not suitable for the indicated step?

  • Step 1: concentrated HNO3 and concentrated H2SO4

  • Step 2: Sn and HCl

  • Step 3: Cl2

  • Step 4: AlCl3 and CH3COCl

Choose your answer

4
1 mark

Molecule X is shown below.

v3M1_VGF_ocr-a2-6-1h-mcq-q4-molecule-x

Which statement(s) is/are correct?

  1. An electrophile reacts with benzene to produce molecule X. The electrophile is formed from AlCl3 and ClCH2COCl.

  2. Molecule X has an isomer that exhibits optical activity and when added to Tollens’ reagent produces a silver mirror.

  3. Molecule X will produce steamy white fumes when added to water at room temperature.

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

Choose your answer

5
1 mark

TNT (2,4,6-trinitromethylbenzene) is formed from methylbenzene in a reaction with a yield of 57.0 %.

What mass of TNT is formed from 6.00 g of methylbenzene?

  • 1.39 g

  • 8.44 g

  • 25.2 g

  • 26.0 g

Choose your answer

6
1 mark

Which row correctly describes the mechanism and the type of bond fission involved when benzene reacts with a mixture of concentrated nitric acid and concentrated sulfuric acid?

Mechanism type

Bond fission during electrophile generation

A

Nucleophilic substitution

Heterolytic

B

Electrophilic substitution

Homolytic

C

Electrophilic substitution

Heterolytic

D

Electrophilic addition

Heterolytic

    Choose your answer