Concept Explanation: Oxymercuration-Demercuration Reaction

This question involves predicting the major product of an oxymercuration-demercuration reaction. This is a specific type of electrophilic addition reaction used to add water (H₂O) across an alkene double bond, following Markovnikov's rule without the possibility of carbocation rearrangements.

Step-by-Step Solution:

Step 1: Analyze the Starting Material

The reactant is a cyclic alkene: cyclopentene. Its structure is a five-membered ring with one double bond.

$Cyclopentene$

Step 2: Understand the Oxymercuration-Demercuration Mechanism

This reaction occurs in two parts:

Oxymercuration: The alkene reacts with mercury(II) acetate, Hg(OAc)₂, in water (H₂O). The electrophilic mercury species (HgOAc⁺) attacks the double bond, forming a mercurinium ion intermediate. Water then acts as a nucleophile and attacks the more substituted carbon of the three-membered ring.
Demercuration: Sodium borohydride (NaBH₄) reduces the organomercury compound, replacing the -HgOAc group with a hydrogen atom.

The overall result is the addition of H and OH across the double bond.

Step 3: Apply Markovnikov's Rule

In the oxymercuration step, water adds to the more substituted carbon. For a symmetric alkene like cyclopentene, both carbons of the double bond are equivalent (secondary carbons). Therefore, the -OH group can add to either carbon with equal probability. The product is an alcohol where the -OH group is attached to one of the ring carbons.

The major product is cyclopentanol.

$Cyclopentanol$

Step 4: Identify the Correct Structure

Compare the given options to the structure of cyclopentanol (a five-membered ring with an -OH group attached). The correct structure is the one that shows a cyclopentane ring with an OH group.

Final Answer:

The major product is the second option: Cyclopentanol structure

Related Topics:

Electrophilic Addition Reactions
Markovnikov's Rule
Hydroboration-Oxidation (Anti-Markovnikov addition)
Acid-Catalyzed Hydration of Alkenes
Carbocation Rearrangements

Key Formulae and Theory:

General Reaction:

$R - CH = CH 2 \overset{1 . Hg (OAc) 2, H 2 O / THF 2 . NaBH 4}{\to} R - CH (OH) - CH 3$

Markovnikov's Rule: In the addition of a protic acid (HX) to an unsymmetrical alkene, the hydrogen atom adds to the carbon with the greater number of hydrogen atoms, and the halide (or other group) adds to the carbon with the fewer hydrogen atoms.

Key Advantage of Oxymercuration-Demercuration: It follows Markovnikov's rule but avoids carbocation rearrangements due to the mercurinium ion intermediate, which is not prone to rearrangement like a carbocation.