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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1:01 minutes

Problem 25b

Textbook Question

Predict the product of the following alkyne reductions.
(b)

Verified step by step guidance

Step 1: Identify the type of reduction being performed on the alkyne. Common reduction methods include catalytic hydrogenation, Lindlar's catalyst (partial reduction to cis-alkene), and dissolving metal reduction (partial reduction to trans-alkene). Determine which method is specified in the problem.

Step 2: Recall the mechanism of the chosen reduction method. For example, catalytic hydrogenation with H₂ and a metal catalyst (e.g., Pd, Pt, or Ni) reduces the alkyne completely to an alkane. Lindlar's catalyst reduces the alkyne to a cis-alkene, while dissolving metal reduction (e.g., Na in liquid NH₃) reduces the alkyne to a trans-alkene.

Step 3: Analyze the structure of the starting alkyne. Determine whether it is terminal (one end has a hydrogen) or internal (both ends are substituted). This can influence the stereochemistry and regioselectivity of the product.

Step 4: Apply the reduction method to the alkyne. For example, if Lindlar's catalyst is used, add H₂ to the triple bond in a syn addition manner, resulting in a cis-alkene. If dissolving metal reduction is used, add H atoms in an anti addition manner, resulting in a trans-alkene.

Step 5: Draw the structure of the predicted product based on the stereochemistry and regiochemistry of the reduction method. Ensure that the product matches the expected outcome of the specified reduction process.

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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 can undergo various reactions, including reductions. Understanding the structure and reactivity of alkynes is crucial for predicting the products of their chemical transformations.

Reduction Reactions

Reduction reactions involve the gain of electrons or the decrease in oxidation state of a molecule. In organic chemistry, this often refers to the addition of hydrogen or the removal of oxygen. For alkynes, reduction can lead to the formation of alkenes or alkanes, depending on the extent of the reduction.

Catalysts in Reduction

Catalysts are substances that increase the rate of a chemical reaction without being consumed in the process. In the context of alkyne reductions, common catalysts include palladium, platinum, or nickel, which facilitate the addition of hydrogen to the triple bond. The choice of catalyst can influence the selectivity and type of product formed.

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Related Practice

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

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)

Textbook Question

Predict the product of the following alkyne reductions.

(a)

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.

(a)

Textbook Question

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