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Ch. 8 - Alkenes 1: Properties and Electrophilic Additions
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 61k(v)

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (v) 1. Hg(OAc)2 , H2O 2. NaBH4
(k) Chemical structure of an alkene with hydrogen atoms, illustrating a reaction with HBr.

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1
Identify the reaction type: The given reagents, Hg(OAc)₂, H₂O followed by NaBH₄, indicate an oxymercuration-demercuration reaction. This reaction is used to hydrate alkenes (add H and OH) without carbocation rearrangement.
Determine the regioselectivity: Oxymercuration-demercuration follows Markovnikov's rule, meaning the OH group will add to the more substituted carbon of the double bond, while the H will add to the less substituted carbon.
Analyze the alkene structure: Examine the position of the double bond in the given alkene. Identify the more substituted carbon (the carbon with more alkyl groups attached) and the less substituted carbon.
Predict the intermediate: In the first step, Hg(OAc)₂ reacts with the alkene to form a mercurinium ion intermediate. Water (H₂O) then attacks the more substituted carbon, leading to the addition of an OH group.
Complete the reaction: In the second step, NaBH₄ reduces the intermediate, replacing the mercury group with a hydrogen atom. The final product is an alcohol with the OH group on the more substituted carbon and the H on the less substituted carbon.

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Markovnikov's Rule

Markovnikov's Rule states that in the addition of HX to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This principle helps predict the regioselectivity of reactions involving alkenes, guiding the formation of more stable carbocations during the reaction.
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Oxymercuration-Demercuration

Oxymercuration-Demercuration is a two-step reaction process used to convert alkenes into alcohols. The first step involves the addition of mercuric acetate (Hg(OAc)₂) and water, which forms a mercurial intermediate. The second step, using sodium borohydride (NaBH₄), reduces the intermediate to yield the corresponding alcohol without rearrangement, ensuring the product follows Markovnikov's Rule.
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General properties of oxymercuration-reduction.

Hydration of Alkenes

Hydration of alkenes refers to the addition of water across the double bond of an alkene, resulting in the formation of alcohols. This reaction can occur via acid-catalyzed mechanisms or through oxymercuration-demercuration, and it is crucial for synthesizing alcohols from alkenes while maintaining regioselectivity and stereochemistry.
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Alkyne Hydration