Question 17N.2.sl.TZ0.b
| Date | November 2017 | Marks available | [Maximum mark: 4] | Reference code | 17N.2.sl.TZ0.b |
| Level | sl | Paper | 2 | Time zone | TZ0 |
| Command term | Explain | Question number | b | Adapted from | N/A |
The reactivity of organic compounds depends on the nature and positions of their functional groups.
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.
