Q10(d). Spectral structure problem: the liquid from acetone and base
On treating acetone with a base, a higher-boiling liquid (b.p. 130 °C) can be isolated from the reaction mixture. The spectral data of this liquid are: IR: 1620 cm⁻¹ (m), 1695 cm⁻¹ (s); ¹H NMR: δ 1.9 (3H, singlet), 2.1 (6H, singlet), 6.15 (1H, singlet); UV: λmax 235 nm; ¹³C NMR: δ 20, 27, 31, 124, 154 and 197; Mass: m/z (RA) 55 (100), 83 (90), 43 (78), 98 (49), 29 (46), 39 (43), 27 (42), 53 (13), 41 (13), 28 (8). Deduce the structure and interpret the spectral data.
Answer in brief
4-Methylpent-3-en-2-one (mesityl oxide), (CH₃)₂C=CH–CO–CH₃, C₆H₁₀O.
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Coversmesityl oxidestructure elucidationaldol condensation of acetoneWoodward rulesα,β-unsaturated ketone
All parts of Question 10
- 10(a) Reformatsky reaction and dehydration; Doebner synthesis10 marks
- 10(b) Electronic transitions of acrylaldehyde; hexane to ethanol5 marks
- 10(c) Thermal [1,3] shift: hydrogen cannot migrate, carbon can5 marks
- 10(d) Spectral structure problem: the liquid from acetone and base10 marks