OCR A-Level Chemistry Synthesis and analytical techniques (02), November 2021: Question 5
1 mark · Medium difficulty · Multiple Choice
Identify the correct statement regarding the reaction of 2-methylcyclopentanone with NaCN(aq)/H+(aq).
Practise this questionQuestion
Question text
5 2-Methylcyclopentanone, shown below, is reacted with NaCN(aq)/H+(aq) to form an organic
product.
O
CH3
2-methylcyclopentanone
Which statement is correct?
A In the mechanism, a CN– ion accepts an electron pair.
B The mechanism is electrophilic addition.
C The organic product has one chiral centre.
D The organic product has the molecular formula C7H11NO.
Your answer
[1]
Mark scheme
Show the mark scheme
5 D 1 AO2.1
How to answer it
Carbonyl Chemistry & Nucleophilic Addition
What this question tests
This question assesses your understanding of carbonyl reaction mechanisms (specifically nucleophilic addition of aqueous sodium cyanide and acid), identification of functional group transformations, determination of molecular formulas from structural changes, and recognition of chiral centres in organic molecules.
Core Evaluation of Statements
✅ Correct Answer: D
Statement D: The organic product has the molecular formula C₇H₁₁NO.
Why it's right: 2-methylcyclopentanone has the formula C₆H₁₀O (5 carbons in the ring + 1 in the methyl group). Adding a cyanide group (-CN) adds 1 carbon and 1 nitrogen atom, resulting in C₇H₁₁NO .
💡 Key Knowledge: Mechanism Type
Statement B check: The reaction is nucleophilic addition, not electrophilic addition. Carbonyl compounds react with nucleophiles because the carbonyl carbon has a partial positive charge (delta plus) due to oxygen's high electronegativity.
🧠 Exam Technique: Systematic Elimination
Check each option methodically. Look out for classic distractors such as misidentifying nucleophiles vs. electrophiles, or miscounting atoms when a functional group is added to a cyclic structure.
❌ Common Errors
Students often incorrectly choose Statement A, thinking a negative ion accepts electrons. In reality, the negatively charged cyanide ion ( CN⁻ ) is an electron pair donor (a nucleophile), not an acceptor.
Topics
Module 6: Organic chemistry and analysis · 6.1 Aromatic compounds, carbonyls and acids · 6.2 Nitrogen compounds, polymers and synthesis
Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.