Q10(c). Thermal [1,3] shift: hydrogen cannot migrate, carbon can
[1,3] sigmatropic migration of hydrogen cannot occur under thermal conditions, but [1,3] sigmatropic migration of carbon can. Justify your answer.
Answer in brief
H has only a 1s orbital, so its allowed thermal (antarafacial) path cannot be reached in a four-membered transition state; carbon uses both lobes of its p-type orbital and migrates suprafacially with inversion.
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Covers[1,3] sigmatropic shiftWoodward–Hoffmann rulessuprafacialantarafacialinversion of configuration
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