Ch. 8 - Alkenes I: Properties and Electrophilic Additions

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 8 - Alkenes I: Properties and Electrophilic Additions

Problem 53b

Chapter 7, Problem 53b

Oxymercuration–reduction, like acid-catalyzed hydration, can be modified to synthesize ethers. Suggest an alkene and the appropriate reaction conditions to synthesize the following ethers.
(b)

Verified step by step guidance

Identify the ether to be synthesized: The given structure is an ether with a cyclohexyl group, a methyl group, and an ethyl group attached to the oxygen atom.

Determine the alkene precursor: To form the ether, consider the alkene that would lead to the desired ether upon oxymercuration-reduction. The alkene should have a double bond where the oxygen will be added.

Select the appropriate alkene: In this case, the alkene could be 1-methylcyclohexene, which has a double bond between the cyclohexyl ring and the methyl group.

Choose the reaction conditions: Oxymercuration-reduction involves two main steps. First, treat the alkene with mercuric acetate (Hg(OAc)₂) in the presence of an alcohol (in this case, ethanol) to form the mercurinium ion intermediate. Then, reduce the intermediate using sodium borohydride (NaBH₄) to form the ether.

Explain the mechanism: During oxymercuration, the alkene reacts with Hg(OAc)₂ to form a mercurinium ion. The alcohol (ethanol) attacks the more substituted carbon, leading to the formation of an ether linkage. The reduction step with NaBH₄ removes the mercury, yielding the final ether product.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Oxymercuration-Reduction

Oxymercuration-reduction is a two-step reaction used to convert alkenes into alcohols. The first step involves the addition of mercuric acetate to the alkene, forming a mercurial intermediate. In the second step, this intermediate is reduced, typically using sodium borohydride, to yield the corresponding alcohol. This method is advantageous because it proceeds via a Markovnikov addition, ensuring that the more substituted carbon receives the hydroxyl group.

Ether Synthesis

Ethers can be synthesized through various methods, one of which involves the reaction of alcohols with alkyl halides or through the alkoxymercuration of alkenes. In the context of oxymercuration-reduction, the reaction can be modified to produce ethers by using an alcohol as a nucleophile instead of water. This results in the formation of an ether when the mercurial intermediate reacts with the alcohol, followed by reduction.

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, while the halide (or hydroxyl group) will attach to the more substituted carbon. This principle is crucial in predicting the outcome of reactions involving alkenes, such as oxymercuration-reduction, as it guides the regioselectivity of product formation, ensuring the desired ether structure is achieved.

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Related Practice

Textbook Question

Oxymercuration–reduction, like acid-catalyzed hydration, can be modified to synthesize ethers. Suggest an alkene and the appropriate reaction conditions to synthesize the following ethers.

(a)

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Textbook Question

Provide an arrow-pushing mechanism, accounting also for the stereochemical outcome, of the first step (oxymercuration) of the three reactions in Figure 8.63.

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Textbook Question

Which is more stable, a carbocation or a mercurinium ion? How do you know?

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Textbook Question

Suggest an alkene to undergo hydroboration–oxidation (1. BH₃ 2. NaOH, H₂O₂) to give exclusively the alcohols shown. Pay close attention to the relative (but not absolute) stereochemical outcome.

(c)

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Textbook Question

Predict the products you would get when the following alkenes undergo (i) hydroboration–oxidation (1. BH₃ 2. NaOH, H₂O₂ or (ii) oxymercuration–reduction [1. Hg(OAc)₂, H₂O 2. NaBH₄].

(a)

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Textbook Question

Predict the products you would get when the following alkenes undergo (ii) oxymercuration–reduction [1. Hg(OAc)₂ , H₂O 2. NaBH₄ ].

(b)

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Oxymercuration–reduction, like acid-catalyzed hydration, can be modified to synthesize ethers. Suggest an alkene and the appropriate reaction conditions to synthesize the following ethers.(b)

Verified video answer for a similar problem:

Key Concepts

Oxymercuration-Reduction

Ether Synthesis

Markovnikov's Rule

Oxymercuration–reduction, like acid-catalyzed hydration, can be modified to synthesize ethers. Suggest an alkene and the appropriate reaction conditions to synthesize the following ethers.
(b)