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Date	May 2017	Marks available	1	Reference code	17M.2.hl.TZ1.6
Level	HL	Paper	2	Time zone	TZ1
Command term	State	Question number	6	Adapted from	N/A

Question

This question is about carbon and chlorine compounds.

Ethane, ${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}}$ , 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]

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, ${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{3}}}{\text{Cl}}$ , can undergo polymerization. Draw a section of the polymer with three repeating units.

[1]

Markscheme

substitution AND «free-»radical

substitution AND chain

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

[1 mark]

Two propagation steps:

${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}} + \bullet {\text{Cl}} \to {{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}} \bullet + {\text{HCl}}$

${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}} \bullet + {\text{C}}{{\text{l}}_{\text{2}}} \to {{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{Cl}} + \bullet {\text{Cl}}$

One termination step:

${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}} \bullet + {{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}} \bullet \to {{\text{C}}_{\text{4}}}{{\text{H}}_{{\text{10}}}}$

${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}} \bullet + \bullet {\text{Cl}} \to {{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{Cl}}$

$\bullet {\text{Cl}} + \bullet {\text{Cl}} \to {\text{C}}{{\text{l}}_{\text{2}}}$

Accept radical without $\bullet$ 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.

${\text{C}} = \frac{{24.27}}{{12.01}} = 2.021$ AND ${\text{H}} = \frac{{4.08}}{{1.01}} = 4.04$ AND ${\text{Cl}} = \frac{{71.65}}{{35.45}} = 2.021$

«hence» CH₂Cl

Accept $\frac{{24.27}}{{12.01}}$ : $\frac{{4.08}}{{1.01}}$ : $\frac{{71.65}}{{35.45}}.$

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