OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2018: Question 3

1 mark · Medium difficulty · Multiple Choice

Identify which of the given organic compounds does not react with nucleophiles.

Practise this question

Question

Multiple choice question 3 asks which compound does not react with nucleophiles, with options A (CH3CH2CHO), B (CH3CHCH2 - note: propene or an alkene/alkane derivative structure), C (CH3CH2COCH3), and D (CH3CH2CH2Cl). An empty answer box and a mark allocation of [1] are shown at the bottom.
Question text

3 Which compound does not react with nucleophiles?

A CH3CH2CHO

B CH3CHCH2

C CH3CH2COCH3

D CH3CH2CH2Cl

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme table indicates the correct answer for question 3 is B, awarding 1 mark.

3 B 1

How to answer it

Identifying Compounds That Do Not React with Nucleophiles

What this question tests

This question assesses your understanding of organic functional groups, specifically their electronic structure and susceptibility to nucleophilic attack. You need to recognize which chemical species act as electrophiles (due to polar bonds or electron-deficient carbon centres) versus alkenes, which are electron-rich and undergo electrophilic addition.

Question 3 Analysis

Multiple Choice Question

Which compound does not react with nucleophiles?

  • A CH₃CH₂CHO (Propanal - Aldehyde)
  • B CH₃CHCH₂ (Propene - Alkene)
  • C CH₃CH₂COCH₃ (Butan-2-one - Ketone)
  • D CH₃CH₂CH₂Cl (1-chloropropane - Haloalkane)

✅ Correct Answer: B

Propene ( CH₃CHCH₂ ) is an alkene. It possesses a region of high electron density due to the pi (π) bond. Because nucleophiles are electron-pair donors (Lewis bases looking for positive charges), they are repelled by electron-rich double bonds. Therefore, alkenes react with electrophiles, not nucleophiles.

💡 Key Knowledge

  • Aldehydes & Ketones (A & C): Contain a polar carbonyl group (C=O). The slightly positive carbon attracts nucleophiles (nucleophilic addition).
  • Haloalkanes (D): Contain a polar carbon-halogen bond (C-Cl). The partially positive carbon attracts nucleophiles (nucleophilic substitution).
  • Alkenes (B): Electron-rich C=O/C=C distinction — the carbon-carbon double bond reacts exclusively with electrophiles via electrophilic addition.

🧠 Exam Technique

When faced with a "does not react" question, evaluate each option systematically by identifying its functional group and determining the type of reagent it reacts with. Cross out options that clearly do undergo the specified reaction type until only the exception remains.

❌ Common Errors

Students sometimes confuse nucleophiles with electrophiles, assuming that because double bonds are reactive sites, they will attract any reactive species indiscriminately. Always match the electronic charge of the reagent (electron-rich nucleophile vs electron-deficient electrophile) to the substrate.

Mark Scheme Allocation: 1 mark for selecting B.

Topics

Module 6: Organic chemistry and analysis · Module 4: Core organic chemistry · 6.1 Aromatic compounds, carbonyls and acids · 4.1 Basic concepts and hydrocarbons · 4.2 Alcohols, haloalkanes and analysis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2018. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.