AQA A-Level Chemistry Paper 3, June 2022: Question 30

1 mark · Easy difficulty · Multiple Choice

Identify which reaction type is not involved in a three-step synthetic sequence from phenylethanone to 1-(3-nitrophenyl)ethyl ethanoate.

Practise this question

Question

A reaction pathway with four chemical structures connected by three arrows. The first structure is phenylethanone, showing a benzene ring with a -COCH3 substituent. The second structure adds an -NO2 group meta to the -COCH3 group. The third structure converts the -COCH3 group into -CH(OH)CH3 with the -NO2 group remaining. The fourth structure converts the -CH(OH)CH3 into -CH(OCOCH3)CH3. The question asks which type of reaction is not involved: A esterification, B hydrolysis, C nitration, or D reduction.
Question text

Which type of reaction is not involved in this reaction sequence?

[1 mark]

A esterification

B hydrolysis

C nitration

D reduction

Mark scheme

Show the mark scheme Mark scheme table row for question 30 showing answer 'B (AO3)', mark '1', and note 'hydrolysis'.

30 B (AO3) 1 hydrolysis

How to answer it

Reaction Types in Aromatic Synthesis

📋 What this question tests

This question assesses your ability to analyze multi-step organic reaction pathways and identify the specific reaction types occurring at each transformation:

  • Recognising electrophilic aromatic substitution (specifically, nitration of a benzene ring).
  • Identifying the reduction of a carbonyl group (ketone) to a secondary alcohol using reducing agents like NaBH₄.
  • Recognising esterification (acylation) of an alcohol using an acyl chloride or acid anhydride.
  • Distinguishing between forward synthetic steps (ester formation) and cleavage reactions (hydrolysis).
Question 30 (1 Mark)

Identifying the Reaction Type Not Present

Analysis of the 3-step synthesis from phenylethanone

📐 Step-by-Step Pathway Analysis

Trace the functional group changes across each arrow:

  1. Step 1
    C₆H₅COCH₃ → NO₂-C₆H₄COCH₃
    An -NO₂ group is introduced onto the benzene ring at position 3. This is nitration (electrophilic substitution).
  2. Step 2
    -COCH₃ → -CH(OH)CH₃
    The ketone carbonyl group ( C=O ) is converted into a secondary alcohol ( -CH(OH)- ). This is a reduction (nucleophilic addition of hydride).
  3. Step 3
    -CH(OH)CH₃ → -CH(OCOCH₃)CH₃
    The alcohol group reacts with an acylating agent (e.g., ethanoic anhydride or ethanoyl chloride) to form an ester. This is esterification.

✅ Correct Answer

Option B: hydrolysis

Mark Scheme:
Award 1 mark for selecting B (AO3).

Since nitration (Step 1), reduction (Step 2), and esterification (Step 3) are all present in the sequence, hydrolysis is the reaction type not involved.

💡 Key Knowledge

  • Nitration reagents: Concentrated HNO₃ and concentrated H₂SO₄ catalyst below 55 °C. The -COCH₃ group is electron-withdrawing and directs substitution to the 3- (meta-) position.
  • Reduction reagents: Aqueous/ethanolic sodium tetrahydridoborate(III), NaBH₄, reduces aldehydes and ketones to alcohols.
  • Esterification: Alcohols react with carboxylic acids (acid catalyst), acyl chlorides (room temp, produces HCl), or acid anhydrides (produces ethanoic acid) to form esters.
  • Hydrolysis: The chemical breakdown of a compound due to reaction with water (e.g. ester → alcohol + carboxylic acid), which is the reverse of Step 3!

🧠 Exam Technique & Traps

  • Spot the negative phrasing: The question asks which reaction is NOT involved. Highlight words like "not", "incorrect", or "least" immediately.
  • Do not confuse esterification with hydrolysis: In Step 3, an ester linkage is being created, not broken. Hydrolysis breaks an ester apart using water or hydroxide ions.
  • Watch the formula notation: -CH(OCOCH₃)CH₃ denotes an ester group ( -O-CO-CH₃ ) attached to the carbon chain, confirming esterification took place.

❌ Common Misconceptions & Errors

  • Confusing reduction with oxidation: Students sometimes see oxygen remaining in the molecule and fail to recognise that adding hydrogen across the C=O double bond decreases the carbon's oxidation state (reduction).
  • Misreading the condensed formula in Step 3: Reading -CH(OCOCH₃)CH₃ too quickly and assuming it is an ether or an anhydride rather than an ethanoate ester.

Topics

Organic Chemistry · 3.3.8 Aldehydes and Ketones · 3.3.9 Carboxylic Acids and Derivatives · 3.3.10 Aromatic Chemistry · 3.3.14 Organic Synthesis

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.