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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3:31 minutes

Problem 40g

Textbook Question

Answer Problem 39, parts a–h, using 2-butyne as the starting material instead of propyne.
g. excess H₂, Pd/C

Verified step by step guidance

Identify the starting material: The starting material is 2-butyne, which is an alkyne with the structure CH3-C≡C-CH3. It contains a triple bond between the second and third carbons.

Understand the reaction conditions: The reaction involves excess H2 (hydrogen gas) and Pd/C (palladium on carbon), which is a catalyst used for hydrogenation reactions. Excess H2 ensures complete hydrogenation of the alkyne.

Determine the reaction type: This is a catalytic hydrogenation reaction. In the presence of Pd/C and excess H2, the alkyne will undergo complete hydrogenation, converting the triple bond into a single bond by adding hydrogen atoms.

Write the reaction mechanism: The triple bond in 2-butyne will first be reduced to a double bond (alkene) by the addition of two hydrogen atoms. Then, the double bond will be further reduced to a single bond (alkane) by the addition of two more hydrogen atoms. The final product will be an alkane.

Predict the product: The complete hydrogenation of 2-butyne will result in butane (CH3-CH2-CH2-CH3), as all π bonds in the alkyne are replaced with σ bonds by the addition of hydrogen atoms.

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Key Concepts

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

Alkyne Hydrogenation

Hydrogenation of alkynes involves the addition of hydrogen (H2) across the triple bond, converting it into an alkene or alkane. In the presence of a catalyst like palladium on carbon (Pd/C), this reaction can proceed efficiently. For 2-butyne, excess H2 will fully saturate the triple bond, resulting in the formation of butane.

Catalytic Hydrogenation

Catalytic hydrogenation is a process where hydrogen gas is added to unsaturated organic compounds in the presence of a catalyst. The catalyst lowers the activation energy required for the reaction, allowing for faster conversion. In this case, Pd/C serves as an effective catalyst for the hydrogenation of 2-butyne to butane.

Reaction Mechanism

Understanding the reaction mechanism is crucial for predicting the outcome of chemical reactions. In the case of hydrogenation, the mechanism involves the adsorption of the alkyne onto the catalyst surface, followed by the addition of hydrogen atoms to the carbon atoms of the triple bond. This stepwise process leads to the formation of the saturated product, butane, from 2-butyne.

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