OCR A Level Chemistry

Topic Questions

A LevelChemistryOCRTopic Questions6. Organic Chemistry & Analysis (A Level Only)6.1 Benzene & Aromatic Compounds

6.1 Benzene & Aromatic Compounds

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11 mark

What are the reagents 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

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21 mark

Cyclohexene is an unsaturated hydrocarbon and can undergo hydrogenation as shown

Hydrogenation of Cyclohexene

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

Which is the correct explanation?

  • 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

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31 mark

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

  • C6H6COCH3

  • HCl

  • C6H5CH3CO

  • C6H5CH2CH3

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41 mark

Which of the following statements 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

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51 mark

Which part of the following mechanism is not correct?

1-4

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11 mark

Which statements is/are evidence for the modern day model of benzene?

  1. Hydrogenation of benzene is less exothermic than the expectation of cyclohexatriene so benzene is lower in energy.
  2. Each carbon is sp2 hybridised and the remaining p orbital overlaps above and below the plane.
  3. Benzene is planar, has a bond angle of 120o and has equal bond lengths that are smaller than the length of a C=C bond.

  • 1, 2 and 3

  • Only 1 and 2

  • Only 2 and 3

  • Only 1

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21 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. 

  • Nitrobenzene has reduced electron density at positions 3 and 5. 

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

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31 mark

A multi-step mechanism is shown below.
xdHcPPSI_ocr-a2-6-1h-mcq-q3-reaction-sequence

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

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41 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

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51 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

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11 mark

Which of the following 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

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21 mark

Benzene can undergo nitration to form nitrobenzene. Which of the following statements 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

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31 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

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41 mark

The following compound can be synthesised from benzene. 

ocr-a2-6-1m-mcq-q4-phenylpropanone---compound-b

Which reagent is required for this conversion?

  • CH3CH2COOH

  • CH3CH2CH2Cl

  • CH3CH2COCl 

  • CH3CH2CHO

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51 mark

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

  • Bromine

  • Ethanol and concentrated sulfuric acid

  • Sodium hydrogen carbonate 

  • Aqueous potassium hydroxide 

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