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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3:07 minutes

Problem 12a,b

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.

Verified step by step guidance

Step 1: Recognize that the conversion of an alkyne to an alkene involves a reduction reaction. The type of reduction (cis or trans) depends on the reagents used.

Step 2: For part (a), to convert oct-3-yne to cis-oct-3-ene, use Lindlar's catalyst. Lindlar's catalyst is a poisoned palladium catalyst that selectively reduces alkynes to cis-alkenes by adding hydrogen (H₂) in a syn-addition manner.

Step 3: Write the reaction for part (a):

CH_3CH_2C 	ext{≡} CCH_2CH_2CH_2CH_3 + H_2 
ightarrow CH_3CH_2CH=CHCH_2CH_2CH_2CH_3

(cis configuration).

Step 4: For part (b), to convert pent-2-yne to trans-pent-2-ene, use sodium (Na) in liquid ammonia (NH₃). This is a dissolving metal reduction that selectively reduces alkynes to trans-alkenes by adding hydrogen (H₂) in an anti-addition manner.

Step 5: Write the reaction for part (b):

CH_3C 	ext{≡} CCH_2CH_3 + H_2 
ightarrow CH_3CH=CHCH_2CH_3

(trans configuration).

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Key Concepts

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

Alkyne to Alkene Conversion

The conversion of alkynes to alkenes typically involves a process called hydrogenation, where hydrogen gas is added to the alkyne in the presence of a catalyst. This reaction reduces the triple bond of the alkyne to a double bond, forming an alkene. The stereochemistry of the resulting alkene can be controlled by the choice of catalyst and reaction conditions.

Stereochemistry of Alkenes

Stereochemistry refers to the spatial arrangement of atoms in molecules and is crucial for understanding the properties of alkenes. In the case of cis and trans isomers, the terms describe the relative positioning of substituents around the double bond. Cis isomers have substituents on the same side, while trans isomers have them on opposite sides, affecting the physical properties and reactivity of the compounds.

Reagents for Selective Hydrogenation

Selective hydrogenation is a technique used to convert alkynes to specific alkenes while controlling the stereochemistry. Common reagents include Lindlar's catalyst, which allows for the formation of cis alkenes, and sodium in liquid ammonia, which can yield trans alkenes. Understanding the choice of reagents is essential for achieving the desired product in organic synthesis.

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Related Practice

Textbook Question

What are products of the following reactions?

Textbook Question

What stereoisomers are obtained from 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

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)

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (ii) H₂, Pd/C, Pb(OAc)₂ , CaCO₃ (Lindlar's catalyst). If you expect two products, show both.

(c)

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (iii) Na⁰ , NH₃ (liquid), ―33°C . If you expect two products, show both.

(c)

Textbook Question

Predict the product of the following alkyne reductions.

(a)

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