Question 22M.2.sl.TZ2.d(iv)
| Date | May 2022 | Marks available | [Maximum mark: 2] | Reference code | 22M.2.sl.TZ2.d(iv) |
| Level | sl | Paper | 2 | Time zone | TZ2 |
| Command term | Suggest | Question number | d(iv) | Adapted from | N/A |
Carbon forms many compounds.
But-2-ene reacts with hydrogen bromide.
Suggest two differences in the 1H NMR of but-2-ene and the organic product from (d)(ii).
[2]
ALTERNATIVE 1: Any two of:
but-2-ene: 2 signals AND product: 4 signals ✔
but-2-ene: «area ratio» 3:1/6:2 AND product: «area ratio» 3:3:2:1 ✔
product: «has signal at» 3.5-4.4 ppm «and but-2-ene: does not» ✔
but-2-ene: «has signal at» 4.5-6.0 ppm «and product: does not» ✔
ALTERNATIVE 2:
but-2-ene: doublet AND quartet/multiplet/4 ✔
product: doublet AND triplet AND quintet/5/multiplet AND sextet/6/multiplet ✔
Accept “product «has signal at» 1.3–1.4 ppm «and but-2-ene: does not»”.
The comparison of the 1H NMR spectra of the two organic compounds was more challenging and 10% of the candidates left this question blank. The average mark was 0.7 out of 2 marks. Mistakes included non-specific answers that just stated “more signals” or “higher chemical shift”, and stating 3 signals in 2-bromobutane instead of 4 signals. Standard level candidates were expected to use the number of signals and the ratio of the areas under the signals to answer the question since they do not cover chemical shift, however, many of them did use the 1H NMR section in the data booklet to obtain correct answers in terms of chemical shift.
