Indian Forest Service (Mains), Chemistry optional · 2021 · Paper II
Q3(a)(ii). Strongly shielded internal methyl groups
Question
Explain the methyl-proton resonance at δ = −4.2 ppm in the bridged aromatic structure shown in the paper. [structure given in the paper]
Answer in brief
The methyl groups lie inside the shielding region of the surrounding aromatic π-electron circuit.
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Coversring currentdiamagnetic anisotropynegative chemical shiftbridged annulene¹H NMR shielding
All parts of Question 3
- 3(a)(i) Hydrogen exchange in cyclopropyl ketones5 marks
- 3(a)(ii) Strongly shielded internal methyl groups5 marks
- 3(b)(i) Carbon–carbon bond formation from a bromoester5 marks
- 3(b)(ii) Intramolecular aldol condensation5 marks
- 3(c)(i) ESR resonance field5 marks
- 3(c)(ii) Aromaticity of five-membered heterocycles5 marks
- 3(d)(i) Haworth synthesis of a methoxytetralone5 marks
- 3(d)(ii) Cyanide substitution on a nitroaryl halide5 marks