Question 19M.2.sl.TZ1.1
| Date | May 2019 | Marks available | [Maximum mark: 7] | Reference code | 19M.2.sl.TZ1.1 |
| Level | sl | Paper | 2 | Time zone | TZ1 |
| Command term | Draw, Identify, State | Question number | 1 | Adapted from | N/A |
Xylene is a derivative of benzene. One isomer is 1,4-dimethylbenzene.
State the number of 1H NMR signals for this isomer of xylene and the ratio in which they appear.
Number of signals:
Ratio:
[2]
Number of signals:
2 [✔]
Ratio:
3 : 2
OR
6 : 4 [✔]
Note: Accept any correct integer or fractional ratio.
Accept ratios in reverse order.
Most students gained M1 but very few gained M2, suggesting that the correct answer of 2 signals may have been a guess.
Draw the structure of one other isomer of xylene which retains the benzene ring.
[1]
[✔]
Another isomer of xylene was generally correctly drawn, but some candidates drew the original compound.
Bromine reacts with alkanes.
Identify the initiation step of the reaction and its conditions.
[2]
Br2 → 2Br• [✔]
«sun»light/UV/hv
OR
high temperature [✔]
Note: Do not penalize missing radical symbol on Br.
Accept “homolytic fission of bromine” for M1.
Drawing or describing the homolytic fission of bromine was generally done well.
1,4-dimethylbenzene reacts as a substituted alkane. Draw the structures of the two products of the overall reaction when one molecule of bromine reacts with one molecule of 1,4-dimethylbenzene.
[2]
[✔]
HBr [✔]
Note: Accept condensed formulae, such as CH3C6H4CH2Br.
Accept skeletal structures.
Very few students gained 2 marks finding hard to apply their knowledge of free radical substitution to a benzene containing compound. Many thought that the bromine will attach to the benzene ring or would substitute the alkyl group twice and not produce HBr.