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Date November 2016 Marks available 1 Reference code 16N.2.hl.TZ0.6
Level HL Paper 2 Time zone TZ0
Command term Suggest Question number 6 Adapted from N/A

Question

One structural isomer of C4H9Br is a chiral molecule.

Draw the three-dimensional shape of each enantiomer of this isomer showing their spatial relationship to each other.

[2]
a.

When one enantiomer undergoes substitution by alkaline hydrolysis approximately 75 % of the product molecules show inversion of configuration. Comment on the mechanisms that occur.

[2]
b.

Suggest why the rate of alkaline hydrolysis of an enantiomer of iodopropane is greater than that of an enantiomer of bromopropane.

[1]
c.

Markscheme

correct isomer
mirror image shown clearly

a.

SN2 would give inversion of configuration «almost 100%»
OR
SN1 would give «approximately» 50% of each

so mechanism is a mixture of both mechanisms

b.

C–I bond «longer, so» weaker «than C–Br bond»
OR
I is a better leaving group than Br

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Additional higher level (AHL) » Topic 20: Organic chemistry » 20.1 Types of organic reactions
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