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

Previous problemNext problem

5:45 minutes

Problem 19c,d

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.

Verified step by step guidance

Step 1: To synthesize trans-2-pentene, start with an alkyne that has the same carbon backbone as the desired product. In this case, the alkyne should be 2-pentyne (CH≡C-CH2-CH2-CH3). This ensures the correct positioning of the double bond in the final product.

Step 2: Use a reduction reaction to convert the alkyne into the trans-alkene. The appropriate reagent for this transformation is sodium (Na) in liquid ammonia (NH3). This method selectively produces the trans-alkene due to the anti-addition mechanism.

Step 3: For the synthesis of 1-hexene, start with an alkyne that has the same carbon backbone as the desired product. In this case, the alkyne should be 1-hexyne (CH≡C-CH2-CH2-CH2-CH2-CH3). This ensures the double bond forms at the terminal position.

Step 4: Use a partial hydrogenation reaction to convert the alkyne into the alkene. The appropriate reagent for this transformation is Lindlar's catalyst (Pd/CaCO3 with quinoline). This method selectively produces the cis-alkene, but since 1-hexene is terminal, the stereochemistry is not relevant.

Step 5: Verify the product structures by considering the regioselectivity and stereoselectivity of the reactions. Ensure that the reagents used align with the desired product (trans-2-pentene or 1-hexene) and avoid over-reduction to alkanes.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

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 be represented by the general formula CnH2n-2. Understanding the structure and reactivity of alkynes is crucial for synthesizing alkenes, as they can undergo various reactions, including hydrogenation and elimination, to form alkenes like trans-2-pentene and 1-hexene.

Hydrogenation

Hydrogenation is a chemical reaction that involves the addition of hydrogen (H2) to an unsaturated compound, such as an alkyne or alkene, to convert it into a saturated compound. This process is essential for synthesizing alkenes from alkynes, as it can selectively reduce the triple bond to a double bond, allowing for the formation of specific isomers like trans-2-pentene.

Reagents for Synthesis

The choice of reagents is critical in organic synthesis, as they determine the pathway and outcome of the reaction. For synthesizing trans-2-pentene from an alkyne, reagents such as Lindlar's catalyst (for partial hydrogenation) or sodium in liquid ammonia (for trans-selective reduction) are commonly used. Understanding how these reagents interact with alkynes is key to achieving the desired product.

Watch next

Master The definition of hydrogenation. with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

Identify the product when each of the following reactions is performed on the triglyceride of linoleic acid (linoleate).

(a) H₂ , Pd

513

views

Textbook Question

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

(b)

541

views

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.

827

views

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

608

views

Textbook Question

What reagents would you use for the following syntheses?

c. hexane from 3-hexyne

700

views

Textbook Question

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

604

views

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:

599

views

Textbook Question

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

580

views

Show more practices