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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4:49 minutes

Problem 40h

Textbook Question

Answer Problem 39, parts a–h, using 2-butyne as the starting material instead of propyne.
h. H₂/Lindlar catalyst

Verified step by step guidance

Identify the starting material: The problem specifies 2-butyne as the starting material. This is an alkyne with the structure CH3-C≡C-CH3.

Understand the reagent: H2 with a Lindlar catalyst is used to selectively hydrogenate alkynes to cis-alkenes. The Lindlar catalyst prevents full hydrogenation to an alkane.

Predict the product: When 2-butyne (CH3-C≡C-CH3) reacts with H2/Lindlar catalyst, the triple bond (C≡C) is reduced to a double bond (C=C), and the resulting product is a cis-alkene. The two methyl groups (CH3) on either side of the triple bond will remain in the same relative positions.

Draw the structure of the product: The product will be cis-2-butene, with the structure CH3-CH=CH-CH3, where the two hydrogens added during the reaction are on the same side of the double bond.

Verify stereochemistry: Ensure that the product is the cis-isomer (Z configuration), as the Lindlar catalyst specifically produces the cis-alkene and not the trans-alkene.

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Key Concepts

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

Alkyne Reduction

Alkynes can be reduced to alkenes or alkanes through various catalytic processes. The reduction of 2-butyne specifically involves the addition of hydrogen (H2) across the triple bond, converting it into a double bond (alkene) or a single bond (alkane) depending on the catalyst used.

Lindlar Catalyst

The Lindlar catalyst is a poisoned palladium catalyst that selectively reduces alkynes to cis-alkenes without further reducing them to alkanes. This catalyst is crucial for controlling the degree of hydrogenation, allowing for the formation of specific isomers in organic synthesis.

Stereochemistry of Alkenes

Stereochemistry refers to the spatial arrangement of atoms in molecules and is particularly important in alkenes, which can exist as cis or trans isomers. The use of the Lindlar catalyst in the reduction of 2-butyne will yield cis-2-butene, highlighting the importance of stereochemical considerations in organic reactions.

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