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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2:25 minutes

Problem 23a

Textbook Question

Predict the product of the following hydrogenation reactions run with a poisoned catalyst.
(a)

Verified step by step guidance

Step 1: Understand the concept of hydrogenation with a poisoned catalyst. A poisoned catalyst, such as Lindlar's catalyst, is used to selectively hydrogenate alkynes to alkenes without further reducing the alkene to an alkane.

Step 2: Identify the starting material in the reaction. Determine whether the compound is an alkyne, alkene, or another functional group that can undergo hydrogenation.

Step 3: Recognize the stereochemistry of the reaction. Hydrogenation with a poisoned catalyst typically results in a cis-alkene (Z-configuration) due to the syn addition of hydrogen atoms.

Step 4: Write the reaction mechanism. Show how the alkyne interacts with the poisoned catalyst and hydrogen gas to form the cis-alkene. Use MathML to represent the chemical structures and transformations.

Step 5: Predict the product based on the reaction conditions. Ensure the product is a cis-alkene and verify that no further reduction occurs due to the presence of the poisoned catalyst.

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Key Concepts

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

Hydrogenation

Hydrogenation is a chemical reaction that involves the addition of hydrogen (H2) to unsaturated organic compounds, typically alkenes or alkynes, converting them into saturated hydrocarbons. This process is commonly facilitated by catalysts, which speed up the reaction without being consumed. The reaction can lead to the formation of alkanes, and the conditions under which it occurs can significantly influence the product distribution.

Poisoned Catalyst

A poisoned catalyst is a catalyst that has been intentionally modified or contaminated to reduce its activity. In hydrogenation reactions, a poisoned catalyst selectively inhibits the reaction, allowing for the formation of specific products rather than complete saturation. This is particularly useful in organic synthesis, where controlling the degree of hydrogenation is essential for obtaining desired compounds.

Selectivity in Reactions

Selectivity refers to the preference of a chemical reaction to produce one product over others. In the context of hydrogenation with a poisoned catalyst, selectivity is crucial as it determines which unsaturated bonds are hydrogenated and to what extent. Understanding selectivity helps chemists predict the outcome of reactions and design pathways to synthesize specific molecules efficiently.

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