What products would you expect from...

What products would you expect from oxymercuration-demercuration of the following alkenes?
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{2}$
(b) $\mathrm{CH}_{3}$ $\quad \mathrm{CH}_{3} \mathrm{C}=\mathrm{CHCH}_{2} \mathrm{CH}_{3}$

Key Concepts

Rearrangement Prevention

A key advantage of oxymercuration?demercuration over acid-catalyzed hydration is its prevention of carbocation rearrangements. Since the intermediate is a cyclic mercurinium ion rather than a free carbocation, there is very little opportunity for rearrangement, allowing for more predictable outcomes even when more substituted or potentially unstable carbocation intermediates might form under different conditions.

Anti?Addition Mechanism

Oxymercuration?demercuration occurs via an anti?addition mechanism, where the attacking nucleophile approaches the mercurinium ion from the side opposite to the mercury group. This leads to the formation of trans-products in cyclic systems or syn?configured additions in simple alkenes, depending on the substrate, ensuring that the hydroxyl and hydrogen substituents are added to opposite faces of the double bond.

Markovnikov Regioselectivity

The reaction proceeds with Markovnikov regioselectivity, meaning that the nucleophile (water) attacks the more substituted carbon of the double bond within the mercurinium ion. This results in the attachment of the hydroxyl group at the more substituted carbon after demercuration. The regioselectivity is inherent to the mechanism since the partial positive charge is greater on the more substituted carbon in the cyclic intermediate.

Mercurinium Ion Intermediate

The formation of a mercurinium ion intermediate is central to the mechanism of oxymercuration. When the alkene reacts with mercury(II) acetate, it generates a three?membered ring structure that is electrophilic and thus susceptible to nucleophilic attack by water. This intermediate prevents the formation of a free carbocation, thereby reducing the risk of rearrangements that can sometimes occur in acid-catalyzed hydration reactions.

Oxymercuration?Demercuration

Oxymercuration?demercuration is an electrophilic addition reaction that converts alkenes into alcohols by initially reacting the alkene with mercury(II) acetate in the presence of water. The process avoids carbocation intermediates by forming a cyclic mercurinium ion, and then a reducing agent (typically sodium borohydride) is used to replace the mercury group with a hydrogen. This reaction is valued for its ability to add water across a double bond in a controlled and Markovnikov?selective manner without rearrangements.

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