Question 19M.2.hl.TZ1.1e
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.2.hl.TZ1.1e |
| Level | hl | Paper | 2 | Time zone | TZ1 |
| Command term | Discuss | Question number | e | Adapted from | N/A |
Xylene is a derivative of benzene. One isomer is 1,4-dimethylbenzene.
The organic product is not optically active. Discuss whether or not the organic product is a racemic mixture.
[1]
no AND there is no chiral carbon
OR
no AND there is no carbon with four different substituents/groups [✔]
Note: Accept “no AND no asymmetric carbon
atom”.
One of the most poorly answered questions on the exam with only 10 % of candidates earning this mark. Some candidates just answered ‘yes’ or ‘no’ on whether the organic product is a racemic mix and very few mentioned the absence of a chiral carbon. One teacher though the use of benzene in this question made it unnecessarily tough, stating “the optical activity of benzene has not been covered due to the limited chemistry of benzene included in the specification. An aliphatic compound here would test the understanding of enantiomers without the confusion of adding benzene”. Candidates should recognize that carbon in benzene cannot be the centre of optical activity and look for chiral carbons in the substitution chains.
