DP Chemistry (last assessment 2024)

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Question 19M.2.hl.TZ2.6c

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.hl.TZ2.6c
Level hl Paper 2 Time zone TZ2
Command term Compare and contrast Question number c Adapted from N/A
c.
[Maximum mark: 2]
19M.2.hl.TZ2.6c

Phenylethene can be polymerized to form polyphenylethene (polystyrene, PS).

(c)

The benzene ring of phenylethene reacts with the nitronium ion, NO2+, and the C=C double bond reacts with hydrogen bromide, HBr.

Compare and contrast these two reactions in terms of their reaction mechanisms.

 

Similarity: 

Difference:

[2]

Markscheme

Similarity: 
«both» involve an electrophile
OR
«both» electrophilic      [✔]

 

Difference:
first/reaction of ring/with NO2+ is substitution/S«E» AND second/reaction of C=C/with HBr is addition/A«E»      [✔]

 

Note: Answer must state which is substitution and which is addition for M2.

Examiners report

The strong candidates were generally able to see the similarity between the two reactions but unexpectedly some could not identify “electrophilic” as a similarity even if they referred to the differences as electrophilic substitution/addition, so probably were unable to understand what was being asked.

Syllabus sections