Final answer:
Oxymercuration-demercuration involves the Markovnikov addition of a hydroxyl group to an alkene, using mercury (II) acetate and sodium borohydride or thiosulfate as reagents, without carbocation rearrangement.
Step-by-step explanation:
When oxymercuration-demercuration occurs to an alkene, the alkene undergoes an addition reaction where mercury (II) acetate (Hg(OAc)₂) in the presence of water or an alcohol is added across the double bond (oxymercuration), followed by a reduction step to remove the mercury (demercuration), typically using sodium borohydride (NaBH₄) or thiosulfate. The result is the addition of a hydroxyl group (-OH) to the less substituted carbon of the double bond in an alkene, which is a Markovnikov addition. This reaction suppresses the formation of carbocations and thus avoids rearrangement that might otherwise occur if a simple acid-catalyzed hydration was carried out.