Organic Chemistry 51C. Lecture 03. Reactions of Organometallic Reagents. (Nowick)
UCI Open・42 minutes read
Engaging discussion on the reactions of carboxylic acids with hydride nucleophiles and organometallic reagents, including the creation and properties of Grignard reagents. Exploration of various strong nucleophiles like lithium aluminum hydride and organolithium reagents in organic chemistry synthesis, with a focus on retrosynthetic analysis for planning complex molecule synthesis.
Insights
- Grignard reagents, like those developed by Victor Grignard, are essential in forming carbon-carbon bonds through reactions with carbonyl compounds, employing a synthetic process involving alkyl halides and magnesium in ether solvents.
- Organolithium reagents, such as RLi compounds, are reactive nucleophiles that can form new carbon-carbon bonds by reacting with organic compounds, showcasing similar reactivity to Grignard reagents but being generated by reacting alkyl or aryl halides with lithium metal.
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Recent questions
What are Grignard reagents?
Grignard reagents are compounds formed by reacting alkyl halides with magnesium in ether solvents, developed by Victor Grignard. They are essential in organic synthesis, creating carbon-carbon bonds with carbonyl compounds through strong nucleophilic and basic properties.
How are organolithium reagents formed?
Organolithium reagents are generated by reacting alkyl or aryl halides with lithium metal in solvents like ethers. These compounds, represented as RLi, are highly reactive and useful in forming new carbon-carbon bonds with organic compounds, similar to Grignard reagents.
What is the significance of acetylide anions?
Acetylide anions are formed by treating alkynes with strong bases like sodamide, resulting in reactive species with a pKa of about 25. They can react strongly with carbonyl compounds, adding to both front and back faces to form racemic products, contributing to diverse organic synthesis pathways.
How do lithium aluminum hydride reactions proceed?
Lithium aluminum hydride is a potent nucleophile that effectively reduces compounds through addition-elimination reactions. This process leads to the formation of products like benzyl alcohol and methanol, involving the addition of two methyl groups to an alcohol product, showcasing its utility in organic transformations.
What is retrosynthetic analysis in organic chemistry?
Retrosynthetic analysis is a powerful tool for planning organic synthesis, allowing chemists to break down complex molecules into simpler components using retrosynthetic arrows. By strategically selecting appropriate reagents and reaction pathways, complex molecules like 4-ethyl-4-octanol can be synthesized from simpler starting materials like propanal, propyl magnesium chloride, and butyl lithium.
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Summary
00:00
"Grignard Reagents: Formation and Properties"
- First time using electronic homework in class, pleased with engagement
- Continuing discussion on Chapter 20, focusing on organometallic reagents
- Exploring reactions of carboxylic acids with hydride nucleophiles and organometallic reagents
- Formation of carbon-carbon bonds through reactions with hydride nucleophiles and organometallic reagents
- Introduction to Grignard reagents, developed by Victor Grignard, Nobel Prize winner in 1912
- Process of creating Grignard reagents using alkyl halides and magnesium in ether solvents
- Synthetic process involving Grignard reagents, carbonyl compounds, and aqueous workup to form carbon-carbon bonds
- Properties of Grignard reagents and organometallic reagents, acting as strong bases due to large electronegativity differences
- Basicity of Grignard reagents based on pKa values of conjugate anions, with alkynes being more acidic than alkanes
- Explanation of acidic properties of alkynes and alkanes as very weak acids, despite not showing typical acidic behavior
18:12
Reactivity of Alkynes and Organolithium Reagents
- Alkynes with 50% s character in the CH bond are weak acids with a pKa of 25.
- Grignard reagents react with water, acting as a base, forming butane and bromomagnesium hydroxide.
- Water, with a pKa of 15.7, reacts with butane, with a pKa of about 50, in a Bronsted acid-Bronsted base reaction.
- Organolithium reagents, like Grignard reagents, are reactive and can be written generically as RLi.
- Organolithium reagents are formed by reacting alkyl or aryl halides with lithium metal, resulting in compounds like phenyl lithium.
- Organolithium reagents can be generated in ethers and other solvents, reacting with organic compounds like pivaldehyde to form new carbon-carbon bonds.
- Acetylide anions are formed by treating alkynes with strong bases like sodamide, resulting in sodium acetylide anions.
- Acetylide anions, with a pKa of about 25, react strongly with bases like sodamide, forming acetylide anions in high yield.
- Acetylide anions can react with carbonyl compounds like 2-butanone, adding from both the front and back faces to form racemic products.
- Butyl lithium, a strong base and nucleophile, can react with alkynes to form alkynal lithium reagents, useful for making carbon-carbon bonds.
35:57
Strong nucleophiles in organic chemistry reactions
- Tert-butyl lithium is a stronger base compared to N-butyl lithium.
- Treating phenyl acetylene with N-butyl lithium results in lithiated phenyl acetylene, an organolithium compound.
- Reacting lithiated phenyl acetylene with an epoxide followed by an aqueous workup produces an alcohol.
- The alcohol is connected one carbon away from the nucleophile-attacked carbon.
- Various reagents like lithium aluminum hydride and organometallic reagents are strong nucleophiles.
- Carboxylic acids, esters, acid chlorides, and amides are part of the carboxylic acid family.
- Butyl lithium is derived from butene, a fragment of petroleum, making it commonly used.
- Organic chemistry heavily relies on petroleum for various compounds.
- Lithium aluminum hydride is a potent nucleophile that reduces compounds effectively.
- Addition-elimination reactions occur with lithium aluminum hydride, leading to benzyl alcohol and methanol as products.
54:39
"Organic reactions and synthesis strategies explained"
- The reaction involves adding two methyl groups to an alcohol product, similar to a previous reaction via benzaldehyde.
- In this reaction, acetophenone is formed through a ketone reaction with a nucleophile, methyl lithium.
- The ketone is more reactive than the ester, leading to immediate further reactions.
- The reaction involves strong nucleophiles with carboxylic acid family members, with exceptions and variations.
- A general abstraction of strongly basic nucleophiles like lithium aluminum hydride and organolithium reagents is discussed.
- Excess nucleophiles result in the addition of two equivalents, leading to a specific reaction pattern.
- The addition-elimination reaction process is explained, highlighting the breakdown of tetrahedral intermediates.
- Differences between SN2 displacement reactions and addition-elimination reactions are clarified, emphasizing leaving group requirements.
- The importance of leaving group pKa values in different reactions is discussed, with examples provided.
- Retrosynthetic analysis is introduced as a powerful tool for planning organic synthesis, illustrated through a compound synthesis example.
01:14:37
"Retrosynthetic arrow simplifies organic molecule synthesis"
- The use of a retrosynthetic arrow in organic chemistry allows for thinking backward to break down molecules into simpler components for synthesis.
- To synthesize 4-ethyl-4-octanol, starting with propanal, propyl magnesium chloride can be used, followed by oxidation with potassium dichromate to obtain 2-hexanone.
- Further synthesis involves the addition of butyl lithium and an aqueous workup to yield the target molecule.
- The process involves strategic thinking to break down complex molecules into simpler components and then selecting appropriate reagents for synthesis.
