OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2017: Question 13

1 mark · Medium difficulty · Multiple Choice

Identify the reagents used to prepare CH3CH2CONHCH3 from the given multiple-choice options.

Practise this question

Question

Multiple-choice question 13 asking which reagents could be used to prepare CH3CH2CONHCH3. Four options are provided: A (CH3CH2COCl + CH3NH2), B (CH3CH2CONH2 + CH3Br), C (CH3CH2COONa + CH3NH2), and D (CH3CH2COCH3 + NH3), with a box for the student's answer.
Question text

13 Which reagents could be used to prepare CH3CH2CONHCH3?

A CH3CH2COCl + CH3NH2

B CH3CH2CONH2 + CH3Br

C CH3CH2COONa + CH3NH2

D CH3CH2COCH3 + NH3

Your answer

[1]

Mark scheme

Show the mark scheme The mark scheme indicates that the correct answer for question 13 is A, worth 1 mark.

13 A 1

How to answer it

Preparation of N-substituted Amides

What this question tests

This question tests your knowledge of functional group chemistry, specifically the synthesis of secondary (N-substituted) amides via nucleophilic addition-elimination reactions involving acyl chlorides and primary amines.

Question 13

Reagents for Amide Synthesis

Which reagents could be used to prepare CH₃CH₂CONHCH₃ ?

✅ Correct Answer: A

CH₃CH₂COCℓ + CH₃NH₂

An acyl chloride reacts with a primary amine to form an N-substituted amide and hydrogen chloride gas (often trapped with excess amine).

💡 Key Knowledge

  • Target molecule: CH₃CH₂CONHCH₃ is an N-methylpropanamide (an N-substituted amide).
  • Acyl chlorides react readily with primary amines at room temperature in a nucleophilic addition-elimination mechanism.
  • The carbon chain splits into two parts based on the target structure: a 3-carbon acyl group ( CH₃CH₂CO- ) and a 1-carbon alkyl group on the nitrogen ( -CH₃ ).

🧠 Exam Technique

Dissect the target molecule down the peptide/amide bond ( -CO-NH- ). Identify the acyl chain on the carbonyl side and the amine/alkyl chain on the nitrogen side to instantly match the required precursor reagents.

❌ Common Errors

  • Choosing option C ( CH₃CH₂COONa + CH₃NH₂ ): Sodium carboxylates do not react with amines under standard laboratory conditions to form amides.
  • Choosing option B or D, which involve incorrect functional group pairings (halogenoalkanes with primary amides, or ketones with ammonia).
Mark Allocation: [1] mark for selecting option A.

Topics

Module 6: Organic chemistry and analysis · 6.2 Nitrogen compounds, polymers and synthesis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2017. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.