AQA A-Level Chemistry Paper 3, 2021: Question 32

1 mark · Medium difficulty · Multiple Choice

This question checks your understanding of the reactions between amines and halogenoalkanes, focusing on the range of possible products from nucleophilic substitution. It challenges you to recognise the structure of primary, secondary, tertiary amines and quaternary ammonium salts, and spot when a product doesn’t fit the pattern based on the given reactants.

Practise this question

Question

AQA A-Level Chemistry Paper 3, 2021: Question 32
Question text

32 Methylamine reacts with bromoethane by nucleophilic substitution to produce a

mixture of products.

Which is not a possible product of this reaction?

[1 mark]

A C2H5NHCH3

B (C2H5)2NCH3

C [(C H ) N(CH ) ]+ Br –

25 2 3 2

D [(C H ) NCH ]+ Br –

25 3 3

Mark scheme

Show the mark scheme Mark scheme for AQA A-Level Chemistry Paper 3, 2021: Question 32

32 C 1 [(C H ) N(CH ) ]+ Br –

25 2 3 2

How to answer it

Correct Answer: C – [(C2H5)2N(CH3)2]+ Br−

Why? This compound contains two ethyl groups and two methyl groups on the nitrogen. It cannot form from methylamine and bromoethane, as only ethyl groups can be added via this route. Methylamine only has one methyl group to start, and bromoethane adds ethyl groups. To make this quaternary ammonium ion, you’d need two methyl halides and two ethyl halides—so it’s not possible in this specific reaction.

Why A is incorrect:

C2H5NHCH3 is a valid secondary amine formed when methylamine (CH3NH2) reacts once with bromoethane to form a monoalkylated product.

Why B is incorrect:

(C2H5)2NCH3 is a tertiary amine formed when a second ethyl group is added to the nitrogen. Still plausible through successive alkylations with bromoethane.

Why D is incorrect:

[(C2H5)3NCH3]+ Br− is a quaternary ammonium salt that could form through complete alkylation using bromoethane, ending with four substituents on nitrogen (three ethyls, one methyl). This is a valid product from excess bromoethane.

Topics

Organic Chemistry · 3.3.11 Amines

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.