Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

9. Alkenes and Alkynes

Hydrogenation of Alkynes

Organic Chemistry

9. Alkenes and Alkynes

Hydrogenation of Alkynes

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4:20 minutes

Problem 26b

Textbook Question

Suggest alkynes that might be used to make the following trans-alkenes.
(b)

Verified step by step guidance

Identify the trans-alkene product structure. A trans-alkene has two substituents on opposite sides of the double bond. Analyze the given trans-alkene to determine the carbon chain and substituents.

Recall that alkynes can be reduced to trans-alkenes using a dissolving metal reduction, such as sodium (Na) in liquid ammonia (NH₃). This reaction selectively produces trans-alkenes from alkynes.

Determine the alkyne precursor by replacing the double bond in the trans-alkene with a triple bond. This involves identifying the corresponding alkyne structure that would yield the given trans-alkene upon reduction.

Ensure that the alkyne precursor is a terminal or internal alkyne, depending on the structure of the trans-alkene. For example, if the trans-alkene has substituents on both sides of the double bond, the alkyne should be an internal alkyne.

Verify the proposed alkyne by mentally performing the dissolving metal reduction and confirming that the product matches the given trans-alkene. This ensures the correctness of the suggested alkyne precursor.

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Key Concepts

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

Alkynes

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. They are unsaturated compounds and are represented by the general formula CnH2n-2. Alkynes can undergo various reactions, including addition reactions, which are crucial for synthesizing other organic compounds, such as alkenes and alcohols.

Trans-Alkenes

Trans-alkenes are a type of alkene where the substituents on the double bond are on opposite sides, leading to a more stable configuration due to reduced steric strain. The geometric isomerism in alkenes is significant in determining their physical and chemical properties, making it essential to understand how to synthesize them from alkynes.

Hydroboration-Oxidation

Hydroboration-oxidation is a two-step reaction process used to convert alkynes into alkenes. In the first step, an alkyl borane is formed, which adds across the triple bond, followed by oxidation with hydrogen peroxide to yield the corresponding alcohol. This method is particularly useful for synthesizing trans-alkenes due to its regioselectivity and stereochemistry.

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