DP Chemistry (last assessment 2024)

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Question 19M.2.hl.TZ2.6d(i)

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.hl.TZ2.6d(i)
Level hl Paper 2 Time zone TZ2
Command term Outline Question number d(i) Adapted from N/A
d(i).
[Maximum mark: 2]
19M.2.hl.TZ2.6d(i)

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

The major product of the reaction with hydrogen bromide is C6H5–CHBr–CH3 and the minor product is C6H5–CH2–CH2Br.

(d(i))

Outline why the major product, C6H5–CHBr–CH3, can exist in two forms and state the relationship between these forms.

 

Two forms: 

Relationship:

[2]

Markscheme

Two forms:
chiral/asymmetric carbon
OR
carbon atom attached to 4 different groups      [✔]

 

Relationship:
mirror images
OR
enantiomers/optical isomers      [✔]

 

Note: Accept appropriate diagrams for either or both marking points.

Examiners report

Candidates were given the products of the addition reaction and asked about the major product. Perhaps they were put off by the term “forms” and thus failed to “see” the chiral C that allowed the existence of enantiomers. There was some confusion with the type of isomerism and some even suggested cis/trans isomers.

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