Question 22M.2.hl.TZ1.5d(iii)
| Date | May 2022 | Marks available | [Maximum mark: 3] | Reference code | 22M.2.hl.TZ1.5d(iii) |
| Level | hl | Paper | 2 | Time zone | TZ1 |
| Command term | Draw, Explain | Question number | d(iii) | Adapted from | N/A |
Organomagnesium compounds can react with carbonyl compounds. One overall equation is:
Iodomethane is used to prepare CH3Mg. It can also be converted into methanol:
CH3 + HO– → CH3OH + –
Explain the mechanism of the reaction using curly arrows to represent the movement of electron pairs.
[3]
curly arrow going from lone pair/negative charge on O in -OH to C ✔
curly arrow showing I leaving ✔
representation of transition state showing negative charge, square brackets and partial bonds ✔
Accept OH- with or without the lone pair.
Do not allow curly arrows originating on H, rather than the -, in OH-.
Accept curly arrows in the transition state.
Do not penalize if HO and I are not at 180°.
Do not award M3 if OH–C bond is represented.
Award [2 max] if SN1 mechanism shown.
Mechanism for SN2 not done well. Often the negative charge on OH was missing, the curly arrow was not going from lone pair/negative charge on O in -OH to C, or the curly arrow showing I leaving placed incorrectly and specially the negative charge was missing in the transition state. Formation of a carbocation intermediate indicating SN1 mechanism could score a maximum of 2 marks.
