Oxymercuration-Demercuration

Professor Dave Explains
11 Jul 201808:02
EducationalLearning
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TLDRIn this educational video, Professor Dave explains the oxymercuration-demercuration reaction, an addition reaction involving mercury and acetate groups. The process is broken down into two steps: the initial formation of a mercurinium ion intermediate, similar to dihalogenation or halohydrin formation, followed by a reduction step. The reaction results in a Markovnikov hydration, where the hydroxyl group is added to the more substituted carbon of the alkene. The video also touches on the regiochemistry, the variation known as alkoxymercuration-demercuration, and the importance of this technique for synthesizing ethers without carbocation rearrangement.

Takeaways
  • 🌟 Oxymercuration-demercuration is an addition reaction involving mercury and acetate groups, similar to dihalogenation or halohydrin formation.
  • 🔍 The reaction occurs in two steps: the first step forms a mercurinium ion intermediate, and the second step is a reduction to yield the final product.
  • 💧 The reaction results in a Markovnikov hydration, where the hydroxyl group (OH) is added to the more substituted carbon of the double bond.
  • 📚 The mechanism involves the alkene's pi bond acting nucleophilically towards the electron-deficient mercury atom, forming a mercurinium ion intermediate.
  • ⚗️ Water is used to open the mercurinium ion intermediate, leading to the addition of an OH group to the molecule.
  • 🔑 Sodium borohydride is used in the reduction step to complete the hydration process, adding an H atom to the molecule.
  • 📉 The regiochemistry of oxymercuration-demercuration is similar to halohydrin formation, favoring the more substituted carbon for the OH group attachment.
  • 🍸 A variation called alkoxymercuration-demercuration occurs when the reaction is run in alcohol (ROH) instead of water, resulting in an alkoxy group (OR) addition.
  • 🔄 The reaction does not have stereospecificity, leading to the formation of a racemic mixture at the newly formed chiral center.
  • 🛠️ Oxymercuration-demercuration is a useful technique for achieving Markovnikov hydration without carbocation rearrangement, which can be an issue in acid-catalyzed hydrations.
  • 📝 Memorizing the reagent conditions can help predict the Markovnikov hydration outcome, which is a key aspect of the oxymercuration-demercuration process.
Q & A

  • What is oxymercuration-demercuration?

    -Oxymercuration-demercuration is an organic reaction involving the addition of a mercury(II) acetate compound to an alkene, followed by a reduction step to introduce an OH group at the more substituted carbon of the original double bond, resulting in a Markovnikov hydration.

  • What is the role of mercury in the oxymercuration-demercuration process?

    -Mercury acts as an electrophile in the oxymercuration step, forming a mercurinium ion intermediate with the alkene, which is crucial for the subsequent hydration and Markovnikov addition.

  • Why is the oxymercuration-demercuration reaction considered to be a Markovnikov hydration?

    -The oxymercuration-demercuration reaction is a Markovnikov hydration because it follows the Markovnikov's rule, placing the hydroxyl group (OH) on the more substituted carbon of the double bond.

  • What is the solvent system used in the oxymercuration-demercuration reaction?

    -The solvent system is not explicitly mentioned in the script, but typically water is used, which is important for the hydration step of the reaction.

  • How does the mechanism of oxymercuration-demercuration compare to dihalogenation or halohydrin formation?

    -The mechanism of oxymercuration-demercuration is similar to dihalogenation or halohydrin formation in that it involves the formation of an electrophilic intermediate (mercurinium ion) that reacts with a nucleophile (water in this case) to form a new bond.

  • What is the purpose of the reduction step in the oxymercuration-demercuration process?

    -The reduction step, typically using sodium borohydride, serves to remove the mercury atom and introduce a proton (H) to the molecule, completing the hydration process.

  • What is the significance of the regiochemistry in the oxymercuration-demercuration reaction?

    -The regiochemistry is significant because it determines the position of the hydroxyl group addition, ensuring that it follows the Markovnikov's rule and adds to the more substituted carbon.

  • What is alkoxymercuration-demercuration, and how does it differ from oxymercuration-demercuration?

    -Alkoxymercuration-demercuration is a variation of the oxymercuration-demercuration reaction where the reaction is carried out in the presence of an alcohol (ROH) instead of water, resulting in the introduction of an alkoxy group (OR) instead of a hydroxyl group (OH).

  • Why might one choose oxymercuration-demercuration over acid-catalyzed hydration?

    -One might choose oxymercuration-demercuration over acid-catalyzed hydration to avoid carbocation rearrangement, which can occur in acid-catalyzed reactions and lead to undesired products.

  • What is the stereochemical outcome of the oxymercuration-demercuration reaction at the newly formed chiral center?

    -The oxymercuration-demercuration reaction results in a racemic mixture at the newly formed chiral center, meaning both R and S enantiomers are produced.

Outlines
00:00
🔬 Introduction to Oxymercuration-Demercuration

Professor Dave introduces oxymercuration-demercuration, a type of addition reaction similar to dihalogenation and halohydrin formation. The key reagent is a mercury compound with two acetate groups. The reaction proceeds in two steps: the first involves forming a mercurinium ion intermediate, and the second is a reduction using sodium borohydride. This reaction results in Markovnikov hydration, adding an OH group to the more substituted carbon of a double bond without carbocation rearrangement.

05:03
🧪 Mechanism and Regiochemistry of Oxymercuration-Demercuration

The mechanism starts with the alkene's pi bond interacting with an electron-deficient mercury atom, forming a mercurinium ion intermediate. Water then opens this intermediate, adding an OH group. Sodium borohydride reduces the intermediate, completing the hydration. The reaction's regiochemistry places the OH group on the more substituted carbon. This method avoids carbocation rearrangement, providing a reliable Markovnikov hydration. The reaction can be modified to alkoxymercuration-demercuration by using alcohol instead of water, resulting in ether synthesis.

Mindmap
Keywords
💡Oxymercuration-Demercuration
Oxymercuration-demercuration is a two-step organic reaction involving the addition of a mercury(II) compound to an alkene, followed by a reduction to remove the mercury. In the video, this process is discussed as a method to achieve Markovnikov hydration without carbocation rearrangement, which is crucial for maintaining the desired regiochemistry in the product.
💡Markovnikov Hydration
Markovnikov hydration refers to the addition of water across a double bond where the hydroxyl (OH) group attaches to the more substituted carbon atom, following Markovnikov's rule. In the script, this concept is central as it explains the regiochemistry observed in the oxymercuration-demercuration reaction.
💡Acetate Groups
Acetate groups are part of the mercury compound used in the oxymercuration step. They are depicted as 'Ac' in the script and are organic groups consisting of a carbonyl and a methyl group, which are important for the initial formation of the mercurinium ion intermediate.
💡Mercurinium Ion Intermediate
The mercurinium ion intermediate is a key species formed during the oxymercuration step, where the alkene's pi bond interacts with the mercury atom, resulting in a positively charged intermediate similar to a bromonium ion in dihalogenation. The script describes this intermediate as crucial for the subsequent hydration step.
💡Hydration
In the context of the video, hydration refers to the addition of an H and an OH group across the double bond of an alkene. The script uses the term to describe the reaction where water opens the mercurinium ion intermediate, leading to the formation of the alcohol group.
💡Reduction
Reduction in this script refers to the second step of the oxymercuration-demercuration process, where the mercury-containing intermediate is reduced to yield the final product with hydrogen and hydroxyl groups. Sodium borohydride is mentioned as the reducing agent in this step.
💡Regiochemistry
Regiochemistry is the branch of chemistry that deals with the orientation of certain atoms or groups in a molecule. The script emphasizes regiochemistry in the context of the Markovnikov hydration achieved through oxymercuration-demercuration, ensuring the hydroxyl group is added to the more substituted carbon.
💡Alkoxymercuration Demercuration
Alkoxymercuration-demercuration is a variation of the oxymercuration-demercuration process where the reaction is carried out in the presence of an alcohol (ROH) instead of water. The script explains that this variation results in the formation of an ether linkage (OR group) instead of a hydroxyl group.
💡Stereospecificity
Stereospecificity refers to reactions that produce a single stereoisomer from a single reactant. The script mentions the lack of stereospecificity in the oxymercuration-demercuration reaction, leading to the formation of a racemic mixture at the newly formed chiral center.
💡Carbocation Rearrangement
Carbocation rearrangement is a process where a carbocation can shift its charge to a more stable position, often involving the migration of an alkyl group. The script contrasts oxymercuration-demercuration with acid-catalyzed hydration, noting that the former avoids such rearrangements, which can lead to undesired products.
Highlights

Introduction to oxymercuration-demercuration as an addition reaction similar to dihalogenation and halohydrin formation.

Explanation of the oxymercuration-demercuration process involving mercury with two acetate groups.

Description of the solvent system used in the reaction.

Mechanism of the first step in the reaction, leading to the formation of a mercurinium ion intermediate.

Role of water in the hydration step of the reaction, similar to halohydrin formation.

The second step of the reaction involving reduction with sodium borohydride.

Outcome of the reaction as a Markovnikov hydration with regiospecificity.

Placement of the hydroxyl group on the more substituted carbon in the double bond.

General overview of the oxymercuration-demercuration reaction and its comparison to other addition reactions.

Key points on regiochemistry and the formation of the mercurinium ion intermediate.

Discussion on the variation of the reaction known as alkoxymercuration-demercuration.

Difference between oxymercuration-demercuration in water versus alcohol.

Ether synthesis through alkoxymercuration-demercuration.

Practical applications of the reaction for Markovnikov hydration without carbocation rearrangement.

Potential product mixture due to the lack of stereospecificity in the reaction.

Advantages of oxymercuration-demercuration over acid-catalyzed hydration to avoid carbocation rearrangement.

Summary of the oxymercuration-demercuration and alkoxymercuration-demercuration techniques.

Transcripts

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Related Tags
Organic ChemistryMarkovnikov RuleHydration ReactionMercurinium IonAcetate GroupsReduction StepChemical MechanismAlkoxymercurationStereochemistryEther Synthesis