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Date May 2017 Marks available 3 Reference code 17M.2.hl.TZ1.6
Level HL Paper 2 Time zone TZ1
Command term Deduce Question number 6 Adapted from N/A

Question

This question is about carbon and chlorine compounds.

Ethane, C 2 H 6 , reacts with chlorine in sunlight. State the type of this reaction and the name of the mechanism by which it occurs.

M17/4/CHEMI/HP2/ENG/TZ1/06.a

[1]
a.

Formulate equations for the two propagation steps and one termination step in the formation of chloroethane from ethane.

M17/4/CHEMI/HP2/ENG/TZ1/06.bi

[3]
b.i.

Deduce the splitting patterns in the 1H NMR spectrum of C2H5Cl.

[1]
b.ii.

Explain why tetramethylsilane (TMS) is often used as a reference standard in 1H NMR.

[2]
b.iii.

One possible product, X, of the reaction of ethane with chlorine has the following composition by mass:

carbon: 24.27%, hydrogen: 4.08%, chlorine: 71.65%

Determine the empirical formula of the product.

[2]
c.i.

The mass and 1H NMR spectra of product X are shown below. Deduce, giving your reasons, its structural formula and hence the name of the compound.

[3]
c.ii.

When the product X is reacted with NaOH in a hot alcoholic solution, C2H3Cl is formed. State the role of the reactant NaOH other than as a nucleophile.

[1]
c.iii.

Chloroethene, C 2 H 3 Cl , can undergo polymerization. Draw a section of the polymer with three repeating units.

[1]
d.

Markscheme

substitution AND «free-»radical

OR

substitution AND chain

 

Award [1] for “«free-»radical substitution” or “SR” written anywhere in the answer.

[1 mark]

a.

Two propagation steps:

C 2 H 6 + Cl C 2 H 5 + HCl

C 2 H 5 + C l 2 C 2 H 5 Cl + Cl

One termination step:

C 2 H 5 + C 2 H 5 C 4 H 10

OR

C 2 H 5 + Cl C 2 H 5 Cl

OR

Cl + Cl C l 2

 

Accept radical without if consistent throughout.

Allow ECF for incorrect radicals produced in propagation step for M3.

[3 marks]

b.i.

triplet AND quartet

[1 mark]

b.ii.

chemical shift/signal outside range of common chemical shift/signal

strong signal/12/all H atoms in same environment
OR
singlet/no splitting of the signal

volatile/easily separated/easily removed
OR
inert/stabl

contains three common NMR nuclei/1H and 13C and 29Si

 

Do not accept chemical shift = 0.

[2 marks]

b.iii.

C = 24.27 12.01 = 2.021  AND H = 4.08 1.01 = 4.04  AND Cl = 71.65 35.45 = 2.021

«hence» CH2Cl

 

Accept  24.27 12.01 4.08 1.01 : 71.65 35.45 .

Do not accept C2H4Cl2

Award [2] for correct final answer.

[2 marks]

c.i.

molecular ion peak(s) «about» m/z 100 AND «so» C2H4Cl2 «isotopes of Cl»

two signals «in 1H NMR spectrum» AND «so» CH3CHCl2
OR
«signals in» 3:1 ratio «in 1H NMR spectrum» AND «so» CH3CHCl2
OR
one doublet and one quartet «in 1H NMR spectrum» AND «so» CH3CHCl2

1,1-dichloroethane

 

Accept “peaks” for “signals”.

Allow ECF for a correct name for M3 if an incorrect chlorohydrocarbon is identified.

[3 marks]

c.ii.

base
OR
proton acceptor

[1 mark]

c.iii.

M17/4/CHEMI/HP2/ENG/TZ1/06.d/M

 

Continuation bonds must be shown.

Ignore square brackets and “n”.

Accept M17/4/CHEMI/HP2/ENG/TZ1/06.d_2/M .

Accept other versions of the polymer, such as head to head and head to tail.

Accept condensed structure provided all C to C bonds are shown (as single).

[1 mark]

d.

Examiners report

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

Syllabus sections

Core » Topic 10: Organic chemistry » 10.1 Fundamentals of organic chemistry
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