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TReference 1. Hg(OAc)2, H2O 2. NABH, CH3 CH3 H2C H3C Acid-catalyzed addition of water to an alkene yields an alcohol with Markovnikov regiochemistry. The electrophilic H" adds to the sp carbon with the most hydrogens to yield the most stable carbocation intermediate, which then adds water to give the product alcohol. Because a carbocation intermediate is formed, rearrangements can occur prior to the addition of water. To avoid the possibility of rearrangement and still give a Markovnikov alcohol, alkenes can instead be treated with mercury(II) acetate in aqueous THF and then subsequently reduced with sodium borohydride. This reaction proceeds through a cyclic mercurinium ion intermediate which cannot rearrange. Water adds to the cyclic intermediate at the most substituted carbon to give an organomercury alcohol. The reduction step with sodium borohydride is complex and involves radicals. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions OAc ACOH9 :OH2 Hg H20 H2C H2C CH3 CH3

TReference 1. Hg(OAc)2, H2O 2. NABH, CH3 CH3 H2C H3C Acid-catalyzed addition of water to an alkene yields an alcohol with Markovnikov regiochemistry. The electrophilic H" adds to the sp carbon with the most hydrogens to yield the most stable carbocation intermediate, which then adds water to give the product alcohol. Because a carbocation intermediate is formed, rearrangements can occur prior to the addition of water. To avoid the possibility of rearrangement and still give a Markovnikov alcohol, alkenes can instead be treated with mercury(II) acetate in aqueous THF and then subsequently reduced with sodium borohydride. This reaction proceeds through a cyclic mercurinium ion intermediate which cannot rearrange. Water adds to the cyclic intermediate at the most substituted carbon to give an organomercury alcohol. The reduction step with sodium borohydride is complex and involves radicals. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions OAc ACOH9 :OH2 Hg H20 H2C H2C CH3 CH3

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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### Alkene to Alcohol Reaction Using Oxymercuration-Demercuration **Reaction Overview:** An alkene reacts with mercury(II) acetate in the presence of water to form an alcohol with Markovnikov regiochemistry. The reaction follows these steps: 1. **Oxymercuration:** - The alkene is treated with mercury(II) acetate \[(\text{Hg(OAc)}_2)\] and water \[(\text{H}_2\text{O})\]. - This leads to the formation of a mercurinium ion intermediate. - Water molecules then attack the more substituted carbon, yielding an organomercury alcohol. 2. **Demercuration:** - Sodium borohydride \[(\text{NaBH}_4)\] reduces the organomercury compound to an alcohol. **Key Points:** - The addition of water to the alkene happens in a Markovnikov fashion, meaning that the hydroxyl group (\[\text{-OH}\]) attaches to the more substituted carbon. - This method prevents carbocation rearrangement, common in simple acid-catalyzed hydration. **Reaction Mechanism:** - **Initial Stage:** - The \(H^+\) from an acid would typically add to the less substituted carbon; however, in this method, the cyclic mercurinium ion is formed. - **Intermediate Stage:** - Water opens the mercurinium ring, adding to the more substituted carbon. - **Final Reduction:** - Sodium borohydride reduces the intermediate to the final alcohol product. **Arrow-Pushing Guide:** In the diagram, curved arrows indicate electron movement during the reaction steps. Each arrow demonstrates nucleophilic attack or bond formation/cleavage. **Diagram Explanation:** - The initial drawing depicts a mercurinium ion bridging the two carbons of the former double bond. - Water attacks the more substituted carbon, leading to an organomercury intermediate. - This intermediate is represented with mercury bound to one of the carbons, while water adds to the other. Understanding this mechanism highlights efficient ways to synthesize alcohols from alkenes while avoiding carbocation rearrangements.
Transcribed Image Text:### Alkene to Alcohol Reaction Using Oxymercuration-Demercuration **Reaction Overview:** An alkene reacts with mercury(II) acetate in the presence of water to form an alcohol with Markovnikov regiochemistry. The reaction follows these steps: 1. **Oxymercuration:** - The alkene is treated with mercury(II) acetate \[(\text{Hg(OAc)}_2)\] and water \[(\text{H}_2\text{O})\]. - This leads to the formation of a mercurinium ion intermediate. - Water molecules then attack the more substituted carbon, yielding an organomercury alcohol. 2. **Demercuration:** - Sodium borohydride \[(\text{NaBH}_4)\] reduces the organomercury compound to an alcohol. **Key Points:** - The addition of water to the alkene happens in a Markovnikov fashion, meaning that the hydroxyl group (\[\text{-OH}\]) attaches to the more substituted carbon. - This method prevents carbocation rearrangement, common in simple acid-catalyzed hydration. **Reaction Mechanism:** - **Initial Stage:** - The \(H^+\) from an acid would typically add to the less substituted carbon; however, in this method, the cyclic mercurinium ion is formed. - **Intermediate Stage:** - Water opens the mercurinium ring, adding to the more substituted carbon. - **Final Reduction:** - Sodium borohydride reduces the intermediate to the final alcohol product. **Arrow-Pushing Guide:** In the diagram, curved arrows indicate electron movement during the reaction steps. Each arrow demonstrates nucleophilic attack or bond formation/cleavage. **Diagram Explanation:** - The initial drawing depicts a mercurinium ion bridging the two carbons of the former double bond. - Water attacks the more substituted carbon, leading to an organomercury intermediate. - This intermediate is represented with mercury bound to one of the carbons, while water adds to the other. Understanding this mechanism highlights efficient ways to synthesize alcohols from alkenes while avoiding carbocation rearrangements.
**Educational Content on Oxymercuration-Demercuration Mechanism** **Concept Overview:** Acid-catalyzed addition of water to an alkene yields an alcohol with Markovnikov regiochemistry. The electrophilic H⁺ ion adds to the sp² carbon with more hydrogens to form the most stable carbocation intermediate. This intermediate then adds water to yield the alcohol product. Since a carbocation intermediate is formed, rearrangements can occur before water addition. **Alternative Approach to Avoid Rearrangements:** To prevent rearrangements while retaining Markovnikov selectivity, alkenes can be treated with mercury(II) acetate in aqueous THF, followed by reduction with sodium borohydride. This reaction proceeds via a cyclic mercurinium ion intermediate, which is not prone to rearrangement. Water adds to the cyclic intermediate at the more substituted carbon, forming an organomercury alcohol. The sodium borohydride reduction step is complex and involves radical species. **Mechanism Explanation:** - **Arrow-Pushing Instructions:** Use curved arrows to illustrate electron movement during this step of the mechanism. **Chemical Structures:** 1. **Initial Reactants:** Alkene with Hg(OAc)₂, H₂O 2. **Transition State:** Formation of a cyclic mercurinium ion is shown with Hg bridged across the two carbons, one marked with a positive charge, and acetate groups (OAc). 3. **Formation of Organomercury Alcohol:** The water molecule attacks, leading to an intermediate with AcOHg and OH attached to adjacent carbons. This detailed explanation ensures a clear understanding of oxymercuration-demercuration, a vital reaction in organic synthesis, emphasizing mechanism and electron flow.
Transcribed Image Text:**Educational Content on Oxymercuration-Demercuration Mechanism** **Concept Overview:** Acid-catalyzed addition of water to an alkene yields an alcohol with Markovnikov regiochemistry. The electrophilic H⁺ ion adds to the sp² carbon with more hydrogens to form the most stable carbocation intermediate. This intermediate then adds water to yield the alcohol product. Since a carbocation intermediate is formed, rearrangements can occur before water addition. **Alternative Approach to Avoid Rearrangements:** To prevent rearrangements while retaining Markovnikov selectivity, alkenes can be treated with mercury(II) acetate in aqueous THF, followed by reduction with sodium borohydride. This reaction proceeds via a cyclic mercurinium ion intermediate, which is not prone to rearrangement. Water adds to the cyclic intermediate at the more substituted carbon, forming an organomercury alcohol. The sodium borohydride reduction step is complex and involves radical species. **Mechanism Explanation:** - **Arrow-Pushing Instructions:** Use curved arrows to illustrate electron movement during this step of the mechanism. **Chemical Structures:** 1. **Initial Reactants:** Alkene with Hg(OAc)₂, H₂O 2. **Transition State:** Formation of a cyclic mercurinium ion is shown with Hg bridged across the two carbons, one marked with a positive charge, and acetate groups (OAc). 3. **Formation of Organomercury Alcohol:** The water molecule attacks, leading to an intermediate with AcOHg and OH attached to adjacent carbons. This detailed explanation ensures a clear understanding of oxymercuration-demercuration, a vital reaction in organic synthesis, emphasizing mechanism and electron flow.
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