OCR A-Level Chemistry AS Breadth in chemistry (01), November 2020: Question 17

1 mark · Medium difficulty · Multiple Choice

Identify which organic compound can undergo both oxidation with acidified potassium dichromate and an acid-catalyzed elimination reaction.

Practise this question

Question

Multiple-choice question 17 asking which of the four provided skeletal and structural alcohol isomers (A, B, C, D) can react with both K2Cr2O7/H2SO4 in an oxidation reaction and an acid catalyst in an elimination reaction. Structure A shows a secondary alcohol containing an alkene group (CH2=C(CH3)CH(OH)CH3). Structure B shows a tertiary-like carbon chain attached to a secondary alcohol with an alkene group. Structure C shows a tertiary alcohol. Structure D shows a diol.
Question text

17 Which compound could react with both

• K2Cr2O7/H2SO4 in an oxidation reaction and

• an acid catalyst (e.g. H2SO4) in an elimination reaction?

A

OH

B

OH

C

HO

D HO OH

Your answer [1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer is option A.

17 A 1 1.2

How to answer it

Functional Group Reactivity: Oxidation & Elimination

What this question tests

This question assesses your ability to identify specific functional group reactions in organic chemistry. Specifically, it tests whether you can recognize the structural requirements for alcohol oxidation (using acidified potassium dichromate) and acid-catalysed dehydration/elimination of alcohols to form alkenes.

Question 17

Exam Breakdown & Solution

✅ Correct Answer: A

Compound A is the correct choice because it features a secondary alcohol group ( -CH(OH)- ), which can be oxidized to a ketone by K₂Cr₂O₇ / H₂SO₄ , and adjacent hydrogen atoms allowing it to undergo acid-catalysed elimination (dehydration).

💡 Key Knowledge

  • Oxidation: Primary alcohols oxidize to aldehydes then carboxylic acids; secondary alcohols oxidize to ketones; tertiary alcohols do not oxidize.
  • Elimination (Dehydration): Alcohols heated under reflux with an acid catalyst (like concentrated H₂SO₄ or H₃PO₄ ) lose an -OH group and a neighbouring hydrogen atom to form an alkene.

🧠 Exam Technique

Scan the structures systematically for functional groups. Eliminate options that lack the required reacting centres. For dual-requirement questions, check every molecule against both conditions before making your final selection.

❌ Common Errors

  • Confusing tertiary alcohols (like in option C) with secondary alcohols—tertiary alcohols cannot be oxidised.
  • Overlooking existing alkene double bonds in the molecules and assuming they interfere with the required reactions.
  • Failing to count carbon hydrogens correctly when assessing elimination potential.
Mark Scheme Allocation: 1 mark awarded for selecting A. (Specification reference: 2.1.3 Alcohols, 2.1.4 Oxidation/Elimination).

Topics

Module 4: Core organic chemistry · Module 6: Organic chemistry and analysis · 4.2 Alcohols, haloalkanes and analysis

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.