OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2019: Question 6

1 mark · Medium difficulty · Multiple Choice

Identify the organic product formed when a substituted aromatic compound containing both a -CH2Cl group and an aromatic chlorine atom reacts with aqueous potassium hydroxide.

Practise this question

Question

Multiple choice question 6 showing a benzene ring substituted with a -CH2Cl group and a -Cl group reacting with KOH(aq). Four options A, B, C, and D show different possible substituted benzene products with variations of -CH2OH, -CH2Cl, -OH, and -Cl groups attached.
Question text

6 What is the organic product of the reaction below?

CH2Cl

KOH(aq)

Cl

CH2OH

A

Cl

CH2Cl

B

OH

CH2OH

C

OH

HO CH2Cl

D

Cl

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 6 is A.

6 A 1 AO2.5

How to answer it

Halogenoalkane vs Aryl Chloride Hydrolysis

What this question tests

This question tests your understanding of the chemical reactivity and functional group chemistry of halogen-containing organic compounds. Specifically, it contrasts the high reactivity of aliphatic halogenoalkanes (or side-chain halogen groups) towards nucleophilic substitution with the unreactivity of aryl halides (halogens bonded directly to a benzene ring).

Question 6 Multiple Choice Analysis

Core Reaction & Breakdown

✅ Correct Answer: A

The aqueous potassium hydroxide ( KOH(aq) ) undergoes nucleophilic substitution with the aliphatic -CH₂Cl group, converting it into an alcohol ( -CH₂OH ). Meanwhile, the chlorine atom attached directly to the benzene ring ( aryl chloride ) does not react under these mild laboratory conditions.

💡 Key Knowledge

  • Aliphatic Halogenoalkanes: Undergo nucleophilic substitution readily with OH⁻(aq) to form primary alcohols.
  • Aryl Halides: The lone pair of electrons on the chlorine atom interacts sideways with the pi-system of the benzene ring, giving the C–Cl bond partial double-bond character. This makes it much stronger and resistant to nucleophilic attack.

🧠 Exam Technique

Analyze each functional group independently. Check if the halogen is part of an alkyl side-chain or bonded directly to the delocalized ring. Eliminate options where the wrong group has reacted or where unexpected substitutions (like ring substitution shown in D) occur.

❌ Common Errors

  • Choosing B or C by assuming the aryl chloride would hydrolyse into a phenol instead of the side-chain.
  • Choosing D by misinterpreting KOH(aq) as a reagent capable of direct electrophilic or nucleophilic aromatic substitution onto the ring.
Mark Scheme Allocation: Option A = 1 Mark (AO2.5 - Applying chemical knowledge to unfamiliar structural contexts).

Topics

Module 6: Organic chemistry and analysis · 6.1 Aromatic compounds, carbonyls and acids

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.