Indian Forest Service (Mains), Chemistry optional · 2022 · Paper II
Q1(g). Rearrangement during silver-assisted solvolysis
Question
Predict the major product from 2-iodo-3,3-dimethylbutane with AgNO₃ in hot ethanol; give the mechanism.
Answer in brief
2,3-Dimethylbut-2-ene is the expected major elimination product after a 1,2-methyl shift.
Key points
- Ag⁺ facilitates iodide departure by formation of AgI; the initially formed secondary cation is CH₃CH⁺C(CH₃)₃.
- An adjacent methyl migrates with its C–C bonding pair to the cationic carbon, giving the tertiary cation (CH₃)₂CH–C⁺(CH₃)₂.
- Ethanol removes the β-H from the adjacent CH group, giving the highly substituted alkene (CH₃)₂C=C(CH₃)₂.
- Heating favours E1 elimination; solvent capture can also give rearranged ether.
The full model answer
As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.
Covers1,2-methyl shiftWagner–Meerwein rearrangementsilver-assisted solvolysisE1 eliminationcarbocation rearrangement
All parts of Question 1
- 1(a) Pyridine versus imidazole5 marks
- 1(b) Cyanide addition to a hindered enone5 marks
- 1(c) Tracing the nitrile carbon5 marks
- 1(d) Dichlorocarbene trapping5 marks
- 1(e) Substituent effects on aryl negative charge5 marks
- 1(f) Why DMSO accelerates many SN2 reactions5 marks
- 1(g) Rearrangement during silver-assisted solvolysis5 marks
- 1(h) Organolithium and Baeyer–Villiger sequence5 marks