Which of th incorrect statement regarding...

Which of th incorrect statement regarding oxymercuration-demercuration? (a) here rearrangement takes place (b) in the second step demercuration occurs that is, $\mathrm{NaBH}_{4}$ reduces $-\mathrm{HgOAc}_{2}$ group to hydrogen (c) the net reaction is addition of water according to Markovnikov's rule (d) In the first step oxymercuration occurs, that is, water and $\mathrm{Hg}(\mathrm{OAc})_{2}$ add to double bond

Which of th incorrect statement regarding oxymercuration-demercuration?
(a) here rearrangement takes place
(b) in the second step demercuration occurs that is, $\mathrm{NaBH}_{4}$ reduces $-\mathrm{HgOAc}_{2}$ group to hydrogen
(c) the net reaction is addition of water according to Markovnikov's rule
(d) In the first step oxymercuration occurs, that is, water and $\mathrm{Hg}(\mathrm{OAc})_{2}$ add to double bond

Key Concepts

Oxymercuration-Demercuration Reaction

This is a two-step reaction used to convert alkenes into alcohols. In the first step, oxymercuration, an electrophilic mercury acetate reagent reacts with the alkene to create a cyclic mercurinium ion intermediate, which is then attacked by water. The second step, demercuration using sodium borohydride, replaces the mercury fragment with a hydrogen atom, yielding the final alcohol product.

Mercurinium Ion Intermediate

The oxymercuration step proceeds via the formation of a mercurinium ion intermediate, which is a three-membered ring species. Its cyclic structure prevents the formation of free carbocations, thereby avoiding rearrangement problems common in typical electrophilic additions and ensuring a regioselective addition of water.

Carbocation Rearrangement

Carbocation rearrangement is a process where an unstable carbocation intermediate shifts its structure to form a more stable carbocation, often leading to unexpected products. In the context of oxymercuration, the mechanism avoids free carbocations, thus preventing any rearrangement, which is a key advantage over other hydration methods.

Markovnikov's Rule

Markovnikov's rule predicts that in the addition of a protic acid to an alkene, the hydrogen atom attaches to the carbon with more hydrogen atoms, while the other additive attaches to the more substituted carbon. Although the net effect in oxymercuration-demercuration follows Markovnikov's orientation, the mechanism itself avoids the formation of a free carbocation, thereby reducing the possibility of rearrangements.

Role of NaBH4 in Demercuration

Sodium borohydride (NaBH4) is a reducing agent used in the demercuration step. It reduces the organomercury intermediate by substituting the mercury acetate group with a hydrogen atom, thus completing the transformation from alkene to alcohol while removing toxic mercury residues.

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