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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3:00 minutes

Problem 26c

Textbook Question

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

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 adding a triple bond in place of the double bond in the trans-alkene. This involves identifying the two carbons involved in the double bond and converting it into a triple bond.

Ensure that the alkyne precursor has the correct number of carbons and substituents to match the trans-alkene product after reduction. Verify that the structure of the alkyne aligns with the desired trans-alkene.

Propose the alkyne(s) that could be used as starting materials. For example, if the trans-alkene has substituents on opposite sides, the corresponding alkyne should have the same substituents attached to the triple bond carbons.

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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 either side of the double bond are positioned on opposite sides, leading to a more stable configuration due to reduced steric strain. The geometric isomerism in alkenes is significant in organic chemistry, as it affects the physical and chemical properties of the compounds.

Elimination Reactions

Elimination reactions involve the removal of atoms or groups from a molecule, resulting in the formation of a double or triple bond. In the context of synthesizing trans-alkenes from alkynes, a common method is the partial hydrogenation of alkynes or the elimination of a leaving group from a precursor compound, which can yield the desired trans configuration.

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