Silver promotes halide departure and the hydroxyl-bearing substrate undergoes a stereoelectronically controlled semipinacol rearrangement. The bond able to migrate must align with the departing C–Br bond. In one stereoisomer the suitable migrating carbon–carbon bond contracts the ring to a cyclopentanecarbaldehyde; in the other, the suitable hydride shift retains the six-membered ring and forms a cyclohexanone. Applying the drawn chair geometries gives P = the ketone and Q = the contracted aldehyde, C. The stereoisomers therefore need not give the same skeleton.
More Types of Reactions: Nucleophilic and electrophilic substitution reactions (both aromatic and aliphatic). Addition reactions to carbon-carbon and carbon-heteroatom (N and O) multiple bonds. Elimination reactions. Reactive intermediates – carbocation, carbanion, carbenes, nitrenes, arynes and free radicals. Molecular rearrangements. Barton decarboxylation and Barton-McCombie reaction, Hunsdiecker reaction. questions
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