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.

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

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

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

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.

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.

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.

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

substitution AND «free-»radical

OR

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:

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

OR

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

OR

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

Accept radical without $\bullet$ if consistent throughout.

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

[3 marks]

triplet AND quartet

[1 mark]

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]

${\text{C}} = \frac{{24.27}}{{12.01}} = 2.021$ 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]

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]

base
OR
proton acceptor

[1 mark]

Continuation bonds must be shown.

Ignore square brackets and “n”.

Accept  .

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]