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

2:18 minutes

Problem 23b

Textbook Question

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

Verified step by step guidance

Identify the type of reaction: Hydrogenation with a poisoned catalyst typically refers to a partial hydrogenation reaction. A common example is the use of Lindlar's catalyst, which selectively hydrogenates alkynes to cis-alkenes without further reducing the alkene to an alkane.

Examine the starting material: Determine if the compound is an alkyne, as this is the typical substrate for partial hydrogenation with a poisoned catalyst. If it is an alkyne, note whether it is terminal or internal.

Understand the stereochemistry: Hydrogenation with a poisoned catalyst like Lindlar's catalyst adds hydrogen atoms to the alkyne in a syn-addition manner, resulting in a cis-alkene as the product.

Write the reaction mechanism: Show the addition of hydrogen atoms to the triple bond of the alkyne, breaking one π-bond to form a double bond. Ensure that the hydrogens are added to the same side of the molecule to produce the cis-alkene.

Predict the product: Based on the mechanism and stereochemistry, draw the structure of the resulting cis-alkene. Ensure that the product reflects the selective partial hydrogenation and does not proceed to a fully saturated alkane.

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.

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 increase the reaction rate 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 can selectively inhibit certain pathways, leading to specific products rather than a complete saturation of all double or triple bonds. This is particularly useful in organic synthesis, where controlling the degree of hydrogenation is crucial for obtaining desired compounds.

Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to occur at one location over another in a molecule, resulting in the formation of a specific isomer. In the context of hydrogenation reactions, the regioselectivity can be influenced by the type of catalyst used, including poisoned catalysts, which can favor the addition of hydrogen to certain positions on a double bond. Understanding regioselectivity is essential for predicting the outcome of reactions and designing synthetic pathways.

Watch next

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

Start learning