Q2(b). E2 in a locked trans-decalin and in locked 1,2-dibromocyclohexanes
On attempted E₂ reaction, A reacted much faster than B, while C reacted much faster than D. Explain with writing the product of the reaction in each case.
[A] [B] [C] [D]
Answer in brief
E2 in rings needs trans-diaxial H and Br. A (Br axial) eliminates fast to trans-2-deuterio-4a,8a-dimethyloctalin (D kept) ; B (Br equatorial, locked) is very slow. C (both Br axial) gives trans-3-bromo-5- and cis-3-bromo-6-tert-butylcyclohexene fast; D (both Br equatorial, locked) is very slow.
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CoversH–C–C–Br unit anti-periplanarconformationally lockedaxial position holds Hfast E2equatorial
All parts of Question 2
- 2(a)(i) (S)-2-Bromobutane with HCOOH and with HCOO⁻Na⁺/DMSO5 marks
- 2(a)(ii) 7-Norbornyl and anti-7-norbornenyl tosylates: participation of a C=C5 marks
- 2(b) E2 in a locked trans-decalin and in locked 1,2-dibromocyclohexanes10 marks
- 2(c)(i) Bromolactonisation of endo-norbornene-carboxylic acid5 marks
- 2(c)(ii) Octalin to the tertiary and the secondary decalol5 marks
- 2(d) Aromatic character of sydnones10 marks