Question 17N.2.sl.TZ0.6
| Date | November 2017 | Marks available | [Maximum mark: 11] | Reference code | 17N.2.sl.TZ0.6 |
| Level | sl | Paper | 2 | Time zone | TZ0 |
| Command term | Deduce, Explain, State | Question number | 6 | Adapted from | N/A |
The reactivity of organic compounds depends on the nature and positions of their functional groups.
The structural formulas of two organic compounds are shown below.
Deduce the type of chemical reaction and the reagents used to distinguish between these compounds.
[1]
oxidation/redox AND acidified «potassium» dichromate(VI)
OR
oxidation/redox AND «acidified potassium» manganate(VII)
Accept “acidified «potassium» dichromate” OR “«acidified potassium» permanganate”.
Accept name or formula of the reagent(s).
State the observation expected for each reaction giving your reasons.
[2]
ALTERNATIVE 1 using K2Cr2O7:
Compound A: orange to green AND secondary hydroxyl
OR
Compound A: orange to green AND hydroxyl oxidized «by chromium(VI) ions»
Compound B: no change AND tertiary hydroxyl «not oxidized by chromium(VI) ions»
Award [1] for “A: orange to green AND B: no change”.
Award [1] for “A: secondary hydroxyl AND B: tertiary hydroxyl”.
ALTERNATIVE 2 using KMnO4:
Compound A: purple to colourless AND secondary hydroxyl
OR
Compound A: purple to colourless AND hydroxyl oxidized «by manganese(VII) ions»
Compound B: no change AND tertiary hydroxyl «not oxidized by manganese(VII) ions»
Accept “alcohol” for “hydroxyl”.
Award [1] for “A: purple to colourless AND B: no change”
Award [1] for “A: secondary hydroxyl AND B: tertiary hydroxyl”.
Accept “purple to brown” for A.
Deduce the number of signals and the ratio of areas under the signals in the 1H NMR spectra of the two compounds.
[4]
Accept ratio of areas in any order.
Do not apply ECF for ratios.
Explain, with the help of equations, the mechanism of the free-radical substitution reaction of ethane with bromine in presence of sunlight.
[4]
Initiation:
Br2 
2Br•
Propagation:
Br• + C2H6 → C2H5• + HBr
C2H5• + Br2 → C2H5Br + Br•
Termination:
Br• + Br• → Br2
OR
C2H5• + Br• → C2H5Br
OR
C2H5• + C2H5• → C4H10
Reference to UV/hν/heat not required.
Accept representation of radical without • (eg, Br, C2H5) if consistent throughout mechanism.
Accept further bromination.
Award [3 max] if initiation, propagation and termination are not stated or are incorrectly labelled for equations.
Award [3 max] if methane is used instead of ethane, and/or chlorine is used instead of bromine.
