9.3 Synthesis of Alkynes | Organic Chemistry

Chad's Prep
4 Dec 202008:07
EducationalLearning
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TLDRThe video transcript focuses on the synthesis of alkynes, a topic within the broader study of organic chemistry. It explains that creating alkynes shares similarities with alkene synthesis but involves a unique twist, specifically utilizing E2 elimination reactions. The process requires a strong base, such as sodium amide, to facilitate two successive E2 eliminations, leading to the formation of a terminal alkyne. The video also touches on the concept of kinetic versus thermodynamic products, noting that terminal alkynes are kinetic products, while internal alkynes are more stable thermodynamically. However, the formation of internal alkynes is not commonly covered in many courses. The transcript concludes with a mention of the 'zipper reaction,' which is not typically part of standard organic chemistry curriculum. The lesson is part of a series that will be released weekly throughout the 2020-21 school year, encouraging viewers to subscribe for updates.

Takeaways
  • πŸ§ͺ The lesson focuses on synthesizing alkynes, a topic that builds upon earlier discussions of alkyne naming and properties.
  • πŸ“š This lesson is part of an ongoing Organic Chemistry playlist aimed at students throughout the 2020-21 school year, with weekly releases.
  • πŸ” Similar to alkenes, alkynes can be formed using E2 elimination reactions, but unlike alkenes, E2 is exclusively used for alkynes.
  • πŸ’‘ The process requires a strong base, such as sodium amide, to effectively perform double dehydrohalogenation.
  • πŸ”¬ A key distinction in the formation of alkynes involves needing either geminal or vicinal dihalides, facilitating two necessary eliminations.
  • ✏️ The lesson primarily focuses on forming terminal alkynes, as internal alkynes are less commonly covered in textbooks and courses.
  • 🧐 Sodium amide is crucial not only for the double elimination steps but also for deprotonating the terminal alkyne, forming an acetylide ion.
  • 🌐 The acetylide ion formation is critical as it completes the reaction with nearly 100% efficiency, ensuring high yield.
  • πŸ’§ The final step of the reaction involves adding water to reprotonate the alkyne, stabilizing the final product.
  • πŸ‘€ For those interested in further study, the script hints at additional complex reactions like forming internal alkynes and the zipper reaction, though these may not be universally taught.
Q & A
  • What is the main topic of this lesson?

    -The main topic of this lesson is the synthesis of alkynes.

  • What is the process used to make alkynes similar to?

    -The process used to make alkynes is similar to making alkenes, specifically using E2 elimination reactions.

  • What type of dihalide is commonly used for forming terminal alkynes?

    -For forming terminal alkynes, a geminal dihalide (two leaving groups on the same carbon) or a vicinal dihalide (two adjacent carbons each with one leaving group) is commonly used.

  • What is the role of sodium amide in the alkyne synthesis process?

    -Sodium amide acts as a strong base that facilitates two successive E2 elimination steps to form the alkyne and also deprotonates the terminal alkyne to form an acetylide ion.

  • Why is sodium amide used in excess during the synthesis of alkynes?

    -Excess sodium amide is used to ensure that the reaction goes to completion, effectively pulling the equilibrium through and providing a good yield.

  • What is the final step in obtaining the alkyne product?

    -The final step is the addition of water to protonate the acetylide ion, yielding the final alkyne product.

  • Why is the formation of an internal alkyne not commonly presented in many textbooks or courses?

    -The formation of an internal alkyne is not commonly presented because the process often leads to the formation of a terminal alkyne as a kinetic product, which is favored due to the strong base used and the subsequent formation of the acetylide ion.

  • What is the thermodynamic product of alkyne formation?

    -The thermodynamic product of alkyne formation is the internal alkyne, which is more stable than the terminal alkyne.

  • What is the 'zipper reaction' and how does it relate to alkyne formation?

    -The 'zipper reaction' is a process where an alkyne formed in the middle of a chain can migrate to the end of the chain in a solution of sodium amide. It is not commonly covered in most organic chemistry courses.

  • What is the importance of the E2 reaction in alkyne synthesis?

    -The E2 reaction is crucial in alkyne synthesis as it is the mechanism by which the alkene intermediate is formed and subsequently transformed into an alkyne through deprotonation and formation of a triple bond.

  • How does the strength of the base used in the second elimination step affect the reaction?

    -The strength of the base used in the second elimination step is critical as it requires an even stronger base than normal to form the alkyne. Sodium amide is used for this purpose due to its high basicity.

  • What is dehydrohalogenation and how does it relate to alkyne synthesis?

    -Dehydrohalogenation is the process of removing a hydrogen and a halogen from a molecule, which is a key step in both alkene and alkyne synthesis. In the context of alkyne synthesis, dehydrohalogenation occurs twice to form the triple bond.

Outlines
00:00
πŸ§ͺ Synthesis of Terminal Alkynes Using E2 Elimination

This paragraph introduces the topic of alkyne synthesis, highlighting the similarities with alkene synthesis but with a specific focus on E2 elimination reactions. It explains the need for a strong base like sodium amide for two successive dehydrohalogenation steps, which are essential for forming a triple bond. The process involves the formation of an alkene intermediate before the final alkyne product is achieved. The paragraph also touches on the concept of terminal alkynes and the use of sodium amide to ensure a high yield through a complete reaction.

05:02
πŸ”¬ Formation of Acetylide Ion and Reaction Equilibrium

The second paragraph delves into the formation of the acetylide ion, a key intermediate in the synthesis of alkynes. It discusses how this step effectively goes to completion, influencing the equilibrium of the reaction and ensuring a favorable outcome. The paragraph explains the necessity of adding water in a subsequent step to protonate and obtain the final product. It also mentions the possibility of forming internal alkynes, which are thermodynamically more stable, but are not commonly covered in most courses. The paragraph concludes with an invitation for feedback and an offer of further resources for those interested in advanced topics.

Mindmap
Keywords
πŸ’‘Alkynes
Alkynes are unsaturated hydrocarbons with at least one carbon-carbon triple bond. They are the focus of the lesson, which discusses their synthesis and reactions. In the script, alkynes are mentioned as the target molecules to be synthesized through a series of chemical reactions.
πŸ’‘E2 Elimination
E2 Elimination is a type of reaction in organic chemistry where a base removes a hydrogen atom from a molecule, leading to the formation of a double or triple bond. The script specifically discusses using E2 elimination to create alkynes, highlighting its importance in the synthesis process.
πŸ’‘Dehydrohalogenation
Dehydrohalogenation is the process of removing a hydrogen and a halogen atom from a molecule, often resulting in the formation of an unsaturated compound. In the context of the video, dehydrohalogenation is a key step in the formation of alkynes from dihalogenated hydrocarbons.
πŸ’‘Geminal Dihalide
A geminal dihalide is a type of organic compound where two halogen atoms are attached to the same carbon atom. In the script, it is mentioned as one of the starting materials for alkyne synthesis, where the two halogens can be removed to form a triple bond.
πŸ’‘Vicinal Dihalide
Vicinal dihalides have two halogen atoms, each attached to adjacent carbon atoms. The script discusses this as another possible starting material for alkyne synthesis, where each carbon can lose a halogen to form a triple bond.
πŸ’‘Terminal Alkynes
Terminal alkynes are a type of alkyne where the triple bond is located at the end of a carbon chain. The video emphasizes the formation of terminal alkynes over internal alkynes, which are less commonly presented in educational materials.
πŸ’‘Sodium Amide
Sodium amide is a strong base used in organic chemistry for deprotonating acids. In the script, it is identified as the super strong base necessary for the second elimination step in forming alkynes, and also for the subsequent deprotonating step to form an acetylide ion.
πŸ’‘Acetylide Ion
The acetylide ion is a negatively charged ion that contains a carbon-carbon triple bond. In the video, it is formed as an intermediate in the synthesis of alkynes and is crucial for driving the reaction to completion due to its stability.
πŸ’‘Thermodynamic Product
The thermodynamic product is the more stable form of a compound that is formed under equilibrium conditions. The script contrasts the kinetic product (formed first) with the thermodynamic product (more stable but not initially formed), noting that the reaction favors the formation of terminal alkynes.
πŸ’‘Kinetic Product
The kinetic product is the compound that is formed preferentially in a reaction under kinetic control, often because it forms more rapidly. The video discusses how the terminal alkyne is the kinetic product of the alkyne synthesis reaction.
πŸ’‘Zipper Reaction
The zipper reaction is a term used to describe a process where an internal alkyne migrates to the end of a carbon chain in the presence of a strong base like sodium amide. The script briefly mentions this reaction as an advanced topic that is not commonly covered in standard organic chemistry courses.
Highlights

The synthesis of alkynes is the topic of this lesson, which is part of an organic chemistry playlist.

Making an alkyne shares similarities with making an alkene, specifically through E2 elimination reactions.

A strong base is required for E2 elimination, with sodium amide being the strongest base used in the process.

Dehydrohalogenation is the process of losing a halogen and a hydrogen from adjacent carbons.

To form an alkyne, dehydrohalogenation must occur twice, requiring two halogens and two hydrogens.

Terminal alkynes are the focus, with leaving groups on the end or second in from the end of the carbon chain.

Internal alkynes are possible but not commonly presented in textbooks or courses.

Sodium amide is used for two successive elimination steps to form a triple bond.

The formation of an alkene is the first step, followed by the formation of an alkyne.

Excess sodium amide present in the solution leads to the formation of an acetylide ion.

The acetylide ion formation is key, as it effectively goes to completion, aiding in achieving a good yield.

Water is added in a final step to protonate and obtain the final alkyne product.

The process can occur with a geminal dihalide or a vicinal dihalide on the terminal carbons.

Internal alkynes are more stable than terminal alkynes, but the formation of terminal alkynes is favored due to the acetylide ion formation.

An alcoholic solution of KOH can be used to form internal alkynes, but this is not commonly taught in organic chemistry courses.

The 'zipper reaction' is a term for when an alkyne migrates to the end of the chain in a solution of sodium amide.

The lesson provides a comprehensive understanding of alkyne synthesis, including the use of strong bases and the formation of acetylide ions.

The channel offers a premium course with study guides, practice problems, and a rapid review for organic chemistry exams.

Transcripts
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