Edexcel A-Level Chemistry AS 10.9 The Mechanisms of the Nucleophilic Substitution Reactions Between Primary Halogenoalkanes and I Aqueous Potassium Hydroxide Questions

Practise Edexcel IAL Chemistry 10.9 by drawing SN2 mechanisms for primary halogenoalkanes with hydroxide or ammonia, including dipoles, lone pairs and leaving ions.

Exam points

Draw SN2 attack from the HO⁻ or NH₃ lone pair to the δ+ carbon of a primary haloalkane.
Show C–X bond electrons moving to X with correct dipoles, charges and leaving ion.
Recognise primary halogenoalkane reactions as nucleophilic substitution and select SN2.

[Maximum number: 4]

This question is about sodium hydroxide.

(a)

Aqueous sodium hydroxide reacts with 1-bromopropane to produce propan-1-ol.

[ 4 ]

(i)

State the type and mechanism of this reaction.

[ 1 ]

An answer that makes reference to the following points:

nucleophilic and substitution

Allow nucleophile

Ignore $\mathrm{S}_{\mathrm{N}} 2$

Do not award $\mathrm{S}_{\mathrm{N}} 1$ , halogenation, nuclear

(1)

(ii)

Complete the mechanism for this reaction.

Include curly arrows, and relevant lone pairs and dipoles.

Figure for Question (ii) — Edexcel A-Level Chemistry AS

[ 3 ]

An answer that makes reference to the following points:

- dipole on C-Br bond

- lone pair on O of $\mathrm{OH}^{-}$

- curly arrow from lone pair to C of C - B r. If no lone pair shown, allow curly arrow from O

- arrow from C-Br to Br or just beyond

- organic product

- $\mathrm{Br}^{-}$

Figure for Answer to Question (ii) — Edexcel A-Level Chemistry AS

Example of mechanism

Allow product as structural formula rather than displayed

Allow NaBr

Ignore $\mathrm{Na}^{+}$

Do not award HBr 6 points correct scores (3)

4 / 5 points correct scores ( 2 )

2 / 3 points correct scores (1) Ignore intermediate/ transition state if shown

(3)

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Edexcel A-Level Chemistry AS 10.9 The Mechanisms of the Nucleophilic Substitution Reactions Between Primary Halogenoalkanes and I Aqueous Potassium Hydroxide Questions question 1

Question (a)

Question (i)

Question (ii)