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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4:31 minutes

Problem 55b

Textbook Question

What stereoisomers are obtained from the following reactions?
b.

Verified step by step guidance

Step 1: Analyze the starting material, which is a terminal alkyne (CH3CH2C≡CCH2CH3). The triple bond is the reactive site in this molecule.

Step 2: The first reaction involves H2 with a Lindlar catalyst. This selectively reduces the alkyne to a cis-alkene. The Lindlar catalyst prevents further reduction to an alkane, ensuring the formation of a cis-alkene stereoisomer.

Step 3: The second reaction involves D2 with Pd/C. This is a catalytic hydrogenation reaction, but instead of H2, D2 is used. The alkene formed in the previous step undergoes syn-addition of deuterium atoms across the double bond, resulting in a fully saturated alkane with deuterium atoms added.

Step 4: Consider stereochemistry. The Lindlar catalyst ensures the cis configuration of the alkene intermediate. The syn-addition of D2 maintains the stereochemical integrity during the second step.

Step 5: The final product is a saturated alkane with deuterium atoms added. The stereoisomers obtained depend on the spatial arrangement of substituents around the original triple bond and the cis-alkene intermediate.

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Key Concepts

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

Stereoisomerism

Stereoisomerism refers to the phenomenon where compounds have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of their atoms. This can lead to different physical and chemical properties. In organic chemistry, stereoisomers can be classified into two main types: geometric isomers (cis/trans) and optical isomers (enantiomers), which are crucial for understanding the outcomes of reactions involving chiral centers.

Hydrogenation of Alkynes

Hydrogenation is a chemical reaction that involves the addition of hydrogen (H2) to an unsaturated compound, such as an alkyne. The use of a Lindlar catalyst allows for the selective partial hydrogenation of alkynes to cis-alkenes, while the use of Pd/C can lead to complete hydrogenation to alkanes. Understanding the conditions and catalysts used in hydrogenation is essential for predicting the stereochemical outcomes of the reaction.

Lindlar Catalyst

The Lindlar catalyst is a palladium-based catalyst that is poisoned to selectively hydrogenate alkynes to cis-alkenes without further reducing them to alkanes. It is crucial in organic synthesis for controlling the degree of hydrogenation and achieving specific stereochemical configurations. Recognizing the role of the Lindlar catalyst helps in predicting the stereoisomers formed during the reaction process.

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Related Practice

Textbook Question

Answer Problem 39, parts a–h, using 2-butyne as the starting material instead of propyne.

h. H₂/Lindlar catalyst

Textbook Question

Answer Problem 39, parts a–h, using 2-butyne as the starting material instead of propyne.

g. excess H₂, Pd/C

Textbook Question

What are products of the following reactions?

Textbook Question

What are products of the following reactions?

Textbook Question

What stereoisomers are obtained from the following reactions?

Textbook Question

The following reaction was recently reported to have been performed electrochemically.

(a) Identify the reagent and a solvent that could have been used if this reaction was done traditionally.

(b) What safety and environmental hazards are improved or worsened when doing this reaction electrochemically?

Textbook Question

Show how you would convert

a. oct-3-yne to cis-oct-3-ene.

b. pent-2-yne to trans-pent-2-ene.

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (i) H₂ , Pd/C; If you expect two products, show both.

(c)

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What stereoisomers are obtained from the following reactions? b.

Key Concepts

Stereoisomerism

Hydrogenation of Alkynes

Lindlar Catalyst

Watch next

What stereoisomers are obtained from the following reactions?
b.