DP Chemistry (last assessment 2024)

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Question 22N.2.hl.TZ0.6f

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Date November 2022 Marks available [Maximum mark: 3] Reference code 22N.2.hl.TZ0.6f
Level hl Paper 2 Time zone TZ0
Command term Justify, State Question number f Adapted from N/A
f.
[Maximum mark: 3]
22N.2.hl.TZ0.6f

2-Bromobutane can react with cyanide, CN−, in a nucleophilic substitution reaction.

(f)

2-Bromobutane reacts with hydroxide via the same mechanism identified in (b). Explain this mechanism using curly arrows to represent the movement of electron pairs.

[3]

Markscheme

arrow from – charge/lone pair to carbon attached to Br ✔

arrow from C-Br bond to Br ✔

transition state representing the partially formed and partially broken bonds ✔


If SN1 was selected in 6 (b):

arrow from C-Br bond to Br ✔

carbocation intermediate ✔

arrow from – charge/lone pair to carbocation ✔

Examiners report

Candidates gained on average just under 2 of the 3 marks for this rather routine mechanism question and the mark achieved seemed to correlate strongly to performance on the rest of the paper. Students need to check the mechanism drawn corresponds to the one previously identified and to give greater care to the start and end points of curly arrows.

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