| Date | May 2016 | Marks available | 5 | Reference code | 16M.2.sl.TZ0.4 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Distinguish, Predict, State, and Suggest | Question number | 4 | Adapted from | N/A |
Question
Alkenes are widely used in the production of polymers. The compound A, shown below, is used in the manufacture of synthetic rubber.
(i) State the name, applying IUPAC rules, of compound A.
(ii) Draw a section, showing three repeating units, of the polymer that can be formed from compound A.
(iii) Compound A is flammable. Formulate the equation for its complete combustion.
Compound B is related to compound A.
(i) State the term that is used to describe molecules that are related to each other in the same way as compound A and compound B.
(ii) Suggest a chemical test to distinguish between compound A and compound B, giving the observation you would expect for each.
Test:
Observation with A:
Observation with B:
(iii) Spectroscopic methods could also be used to distinguish between compounds A and B.
Predict one difference in the IR spectra and one difference in the 1H NMR spectra of these compounds, using sections 26 and 27 of the data booklet.
IR spectra:
1H NMR spectra:
A sample of compound A was prepared in which the 12C in the CH2 group was replaced by 13C.
(i) State the main difference between the mass spectrum of this sample and that of normal compound A.
(ii) State the structure of the nucleus and the orbital diagram of 13C in its ground state.
Draw a 1s atomic orbital and a 2p atomic orbital.
Markscheme
(i)
methylpropene
(ii)
−CH2−C(CH3)2−CH2−C(CH3)2−CH2−C(CH3)2−
Must have continuation bonds at both ends.
Accept any orientation of the monomers, which could give methyl side-chains on neighbouring atoms etc.
(iii)
C4H8 (g) + 6O2 (g) → 4CO2 (g) + 4H2O(l)
(i)
«structural/functional group» isomer«s»
(ii)
Test:
«react with» bromine/Br2 «in the dark»
OR
«react with» bromine water/Br2 (aq) «in the dark»
IR: A would absorb at 1620–1680cm−1 AND B would not
1H NMR: A would have 2 signals AND B would have 1 signal
OR
A would have a signal at 4.5–6.0 ppm AND B would not
OR
A would have a signal at 0.9–1.0 ppm AND B would not
OR
B would have a signal at 1.3–1.4 ppm AND A would not
Accept “peak” for “signal”.
Award [1 max] if students have a correct assignation of a signal, but no comparison, for both IR and NMR.
Accept “B would have a signal at 2.0 ppm” as shown in its 1H NMR spectrum.
(i)
«molecular ion» peak at «m/z =» 57, «not 56»
OR
«molecular ion» peak at one «m/z» higher
OR
will not have a «large» peak at 56
Accept a peak at m/z one greater than the 12C one for any likely fragment.
(ii)
protons: 6 AND neutrons: 7
Accept full arrows.
Accept p orbitals aligned on y− and z−axes, or diagrams correctly showing all three p-orbitals.
Do not accept p-orbitals without a node.
