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Date May 2018 Marks available 1 Reference code 18M.2.hl.TZ1.7
Level HL Paper 2 Time zone TZ1
Command term Outline Question number 7 Adapted from N/A

Question

This question is about the reactions of halogenoalkanes.

Compare and contrast the mechanisms by which 1-chlorobutane, CH3CH2CH2CH2Cl, and 2-chloro-2-methylpropane, (CH3)3CCl, react with aqueous sodium hydroxide, giving two similarities and one difference.

 

[3]
a.

Outline why the rate of reaction of the similar bromo-compounds is faster.

[1]
b.

State the organic product of the reaction between 1-chlorobutane, CH3CH2CH2CH2Cl, and aqueous sodium hydroxide.

[1]
c.i.

Suggest how this product could be synthesized in one step from butanoic acid.

[1]
c.ii.

Deduce the name of the class of compound formed when the product of (c)(i) reacts with butanoic acid.

[1]
c.iii.

Markscheme

Any two similarities:

heterolytic bond breaking

OR

chloride ions leave

 

nucleophilic/OH substitution

both first order with regard to [halogenoalkane]

 

One difference:

CH3CH2CH2CH2Cl is second order/bimolecular/SN2 AND (CH3)3CCl is first order/unimolecular/SN1

OR

CH3CH2CH2CH2Cl rate depends on [OH] AND (CH3)3CCl does not

OR

CH3CH2CH2CH2Cl is one step AND (CH3)3CCl is two steps

OR

(CH3)3CCl involves an intermediate AND CH3CH2CH2CH2Cl does not

OR

CH3CH2CH2CH2Cl has inversion of configuration AND (CH3)3CCl has c. 50 : 50 retention and inversion

 

Do not accept “produces alcohol” or “produces NaCl”.

Accept “substitution in 1-chlorobutane and «some» elimination in 2-chloro-2-methylpropane”.

[3 marks]

a.

C–Br bond weaker than C–Cl bond

 

Accept “Br is a better leaving group”.

Do not accept "bromine is more reactive".

Do not accept “C–Br bond is longer than C–Cl” alone.

[1 mark]

b.

butan-1-ol/CH3CH2CH2CH2OH

 

Do not accept “butanol” for “butan-1-ol”.

Accept “1-butanol”.

Do not penalize for name if correct formula is drawn.

[1 mark]

c.i.

«reduction with» lithium aluminium hydride/LiAlH4

 

Do not accept “sodium borohydride/NaBH4”.

[1 mark]

c.ii.

ester

[1 mark]

c.iii.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.i.
[N/A]
c.ii.
[N/A]
c.iii.

Syllabus sections

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