Q6(b). HBr and a conjugated diene: 1,2- and 1,4-addition
Predict the product(s) of the following reaction. Which product will be major and why? [structure of the conjugated diene given in the paper] + HBr → ?
Answer in brief
1,2-adduct 3-bromo-3-methylcyclohex-1-ene is major under kinetic control (low temperature); 1,4-adduct 3-bromo-1-methylcyclohex-1-ene is major under thermodynamic control (room temperature and above).
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Coversconjugated diene1,2-addition1,4-additionkinetic controlthermodynamic controlallylic cation
All parts of Question 6
- 6(a) Curtius rearrangement; the isocyanate closes to a cyclic urea4 marks
- 6(b) HBr and a conjugated diene: 1,2- and 1,4-addition4 marks
- 6(c) Phenylglycine and mandelic acid from benzaldehyde4 marks
- 6(d) Coumarin and 3-acetylcoumarin from salicylaldehyde4 marks
- 6(e) Intramolecular oxymercuration–demercuration: a cyclic ether4 marks
- 6(f) trans- and cis-Cyclohexane-1,2-diol from cyclohexanone4 marks
- 6(g) [1,5]-Carbon shift and Cope rearrangement4 marks
- 6(h) Four C₁₀H₁₄ isomers: the one marked by a McLafferty peak4 marks
- 6(i) C₃H₇NO with two N–methyl singlets: N,N-dimethylformamide4 marks
- 6(j) ν(C=C) of methylidenecycloalkanes and ring size4 marks