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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2:26 minutes

Problem 38c

Textbook Question

What reagents would you use for the following syntheses?
c. hexane from 3-hexyne

Verified step by step guidance

Step 1: Recognize that the goal is to convert 3-hexyne (an alkyne) into hexane (an alkane). This requires a complete reduction of the triple bond to a single bond.

Step 2: Understand that the reduction of an alkyne to an alkane can be achieved using hydrogen gas (H₂) in the presence of a metal catalyst, such as palladium (Pd) or platinum (Pt). This process is known as catalytic hydrogenation.

Step 3: Note that the reaction typically proceeds in two stages: first, the alkyne is reduced to an alkene, and then the alkene is further reduced to an alkane. Using excess hydrogen gas ensures the reaction goes all the way to the alkane stage.

Step 4: Write the chemical equation for the reaction:

C_{6} H_{10} + 4 H_{2} \to C_{6} H_{14}

. This shows the addition of hydrogen molecules to the alkyne to form hexane.

Step 5: Summarize the reagents needed: Use hydrogen gas (H₂) and a metal catalyst such as palladium (Pd) or platinum (Pt) under appropriate conditions (e.g., room temperature and pressure or slightly elevated conditions).

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Key Concepts

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

Alkyne Reduction

Alkynes can be reduced to alkanes through various methods, typically involving hydrogenation. In this process, the triple bond of the alkyne is converted into a single bond, resulting in the formation of an alkane. Common reagents for this transformation include hydrogen gas (H2) in the presence of a catalyst such as palladium, platinum, or nickel.

Reagents for Synthesis

Choosing the correct reagents is crucial for successful organic synthesis. In the case of synthesizing hexane from 3-hexyne, one would typically use hydrogenation reagents. Understanding the reactivity and selectivity of these reagents helps in determining the most efficient pathway for the desired product.

Mechanism of Hydrogenation

The mechanism of hydrogenation involves the adsorption of the alkyne onto the surface of the metal catalyst, followed by the addition of hydrogen atoms across the triple bond. This process is stereospecific and can lead to the formation of different isomers depending on the conditions used. Familiarity with this mechanism is essential for predicting the outcome of the reaction.

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Related Practice

Textbook Question

Hydrogenation of which alkynes would produce the following cis-alkenes?

(b)

Textbook Question

Long, polarized bonds are also reducible in the same way that the C―C π bond of an alkyne is. Show a mechanism by which a C―Br bond might be reduced by sodium metal.

Textbook Question

What is the major product of the reaction of 1 mol of propyne with each of the following reagents?

g. excess H₂, Pd/C

h. H₂/Lindlar catalyst

Textbook Question

Describe the alkyne you should start with and the reagents you should use if you want to synthesize

c. trans-2-pentene.

d. 1-hexene.

Textbook Question

How can the following compounds be prepared using ethyne as the starting material?

Textbook Question

Show how each of the following compounds can be prepared using the given starting material, any needed inorganic reagents, and any organic compound that has no more than four carbons:

Textbook Question

How can the following compounds be prepared using ethyne as the starting material?

Textbook Question

What are products of the following reactions?

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