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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3:29 minutes

Problem 19b

Textbook Question

Describe the alkyne you should start with and the reagents you should use if you want to synthesize
b. cis-2-butene.

Verified step by step guidance

Step 1: Recognize that cis-2-butene is an alkene with a cis configuration, meaning the two substituents on the double bond are on the same side. To synthesize this, you need to start with an alkyne and perform a partial reduction.

Step 2: Identify the alkyne that can lead to cis-2-butene. The alkyne should have the same carbon skeleton as the desired product. In this case, the starting alkyne is 2-butyne (CH≡C-CH₂-CH₃).

Step 3: Choose the appropriate reagents for partial reduction to achieve the cis configuration. Use Lindlar's catalyst, which is a palladium catalyst poisoned with lead or quinoline, to selectively reduce the alkyne to a cis alkene.

Step 4: Understand the mechanism of the reaction. Lindlar's catalyst facilitates the addition of hydrogen (H₂) to the triple bond in a syn fashion, meaning both hydrogens add to the same side of the molecule, resulting in the cis configuration.

Step 5: Ensure the reaction conditions are mild and avoid over-reduction. Using Lindlar's catalyst prevents the alkyne from being fully reduced to an alkane, stopping at the alkene stage.

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Key Concepts

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

Alkynes

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. They are unsaturated compounds and can participate in various chemical reactions, including addition reactions. Understanding the structure and reactivity of alkynes is crucial for determining the appropriate starting material for synthesizing other compounds, such as alkenes.

Hydroboration-Oxidation

Hydroboration-oxidation is a two-step reaction process used to convert alkynes into alkenes with specific stereochemistry. In the first step, an alkyl borane is formed, which adds across the triple bond. The subsequent oxidation step replaces the boron with a hydroxyl group, leading to the formation of an alcohol that can be dehydrated to yield the desired alkene, such as cis-2-butene.

Stereochemistry

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical properties and reactions. In the case of cis-2-butene, the specific arrangement of substituents around the double bond is crucial for its identification. Understanding stereochemistry is essential for predicting the outcome of reactions and ensuring the correct isomer is synthesized.

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Related Practice

Textbook Question

Show how you would convert

c. cis-cyclodecene to trans-cyclodecene.

Textbook Question

What reaction would acetylene likely undergo if it were kept at 1500°C for too long?

Textbook Question

Hydration of alkynes (via oxymercuration) gives good yields of single compounds only with symmetrical or terminal alkynes. Show what the products would be from hydration of each compound.

d. cyclodecyne

Textbook Question

Predict the product of the following reactions.

(b)

Textbook Question

Describe the alkyne you should start with and the reagents you should use if you want to synthesize

a. pentane.

Textbook Question

We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.

(a)

Textbook Question

What alkene would you start with if you wanted to synthesize

b. ethylcyclopentane?

Textbook Question

a. How many alkenes could you treat with H₂, Pd/C to prepare methylcyclopentane?

b. Which of the alkenes is the most stable?

c. Which of the alkenes has the smallest heat of hydrogenation?

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