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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2:18 minutes

Problem 44c(iii)

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (iii) Na⁰ , NH₃ (liquid), ―33°C . If you expect two products, show both.
(c)

Verified step by step guidance

Identify the reaction type: The given reagents (Na⁰, NH₃ (liquid), ―33°C) indicate a dissolving metal reduction. This reaction is used to reduce alkynes to trans-alkenes.

Understand the mechanism: In a dissolving metal reduction, sodium donates an electron to the alkyne, forming a radical anion. This is followed by protonation from ammonia, and the process repeats to form a trans-alkene.

Determine the starting alkyne structure: Analyze the structure of the alkyne provided in part (c) to identify the triple bond and any substituents attached to it.

Predict the product(s): The triple bond in the alkyne will be reduced to a double bond, specifically forming a trans-alkene. If the alkyne is symmetrical, only one product will form. If it is asymmetrical, two possible trans-alkenes may form due to different substituent arrangements.

Draw the product(s): Represent the trans-alkene(s) with the substituents on opposite sides of the double bond. Ensure the stereochemistry is clear and consistent with the reaction mechanism.

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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 (C≡C). They are unsaturated compounds and can undergo various reactions, including addition and reduction. Understanding the structure and reactivity of alkynes is crucial for predicting the products formed during chemical reactions.

Reduction Reactions

Reduction reactions involve the gain of electrons or the decrease in oxidation state by a molecule. In the context of alkynes, treatment with sodium (Na⁰) in liquid ammonia (NH₃) at low temperatures typically leads to the reduction of the triple bond to a double bond, forming alkenes. This process is essential for understanding how alkynes can be transformed into other organic compounds.

Stereochemistry of Alkenes

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. When alkynes are reduced to alkenes, the resulting double bond can exhibit cis/trans (E/Z) isomerism, depending on the substituents attached to the double bond. Recognizing the potential for different stereoisomers is important for predicting the products of the reaction.

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Related Practice

Textbook Question

The following reaction was recently reported to have been performed electrochemically.

(a) Identify the reagent and a solvent that could have been used if this reaction was done traditionally.

(b) What safety and environmental hazards are improved or worsened when doing this reaction electrochemically?

Textbook Question

Show how you would convert

a. oct-3-yne to cis-oct-3-ene.

b. pent-2-yne to trans-pent-2-ene.

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (i) H₂ , Pd/C; If you expect two products, show both.

(c)

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (ii) H₂, Pd/C, Pb(OAc)₂ , CaCO₃ (Lindlar's catalyst). If you expect two products, show both.

(c)

Textbook Question

Predict the product of the following alkyne reductions.

(a)

Textbook Question

Predict the product of the following alkyne reductions.

(b)

Textbook Question

Predict the product of the following alkyne reductions.

(c)

Textbook Question

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