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

Alkynide Synthesis

Organic Chemistry

9. Alkenes and Alkynes

Alkynide Synthesis

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4:06 minutes

Problem 50b

Textbook Question

Show how the following compounds can be synthesized starting with ethyne:
b. trans-3-heptene

Verified step by step guidance

Step 1: Begin with ethyne (C₂H₂) as the starting material. Ethyne is a simple alkyne with a triple bond between two carbon atoms.

Step 2: Perform a hydroboration-oxidation reaction to convert ethyne into an aldehyde. Use reagents such as disiamylborane (R₂BH) followed by hydrogen peroxide (H₂O₂) and sodium hydroxide (NaOH). This will yield acetaldehyde (CH₃CHO).

Step 3: Perform an aldol condensation reaction. React acetaldehyde with another equivalent of acetaldehyde in the presence of a base (e.g., NaOH) to form crotonaldehyde (CH₃CH=CHCHO), which contains a trans double bond.

Step 4: Extend the carbon chain by performing a Wittig reaction. React crotonaldehyde with a Wittig reagent (e.g., a phosphonium ylide derived from propyl bromide) to form trans-3-heptene. This reaction allows for the selective formation of the trans isomer.

Step 5: Purify the product to isolate trans-3-heptene. Use techniques such as distillation or chromatography to ensure the desired compound is obtained in high purity.

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Key Concepts

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

Ethyne as a Building Block

Ethyne, also known as acetylene, is a simple alkyne that serves as a versatile building block in organic synthesis. Its triple bond allows for various reactions, including addition reactions with electrophiles, which can lead to the formation of longer carbon chains. Understanding how to manipulate ethyne is crucial for synthesizing more complex molecules like trans-3-heptene.

Alkene Synthesis

Alkenes, such as trans-3-heptene, can be synthesized through various methods, including elimination reactions and hydroboration-oxidation. The formation of alkenes from alkynes typically involves partial hydrogenation or elimination of a dihalide. Recognizing the appropriate reaction pathways is essential for constructing the desired alkene from ethyne.

Stereochemistry of Alkenes

Stereochemistry refers to the spatial arrangement of atoms in molecules and is particularly important in alkenes, which can exhibit geometric isomerism. trans-3-heptene has a specific configuration where substituents are on opposite sides of the double bond. Understanding stereochemistry is vital for ensuring the correct isomer is synthesized, as different isomers can have distinct physical and chemical properties.

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Related Practice

Textbook Question

Show how you would synthesize the following compounds, starting with acetylene and any compounds containing no more than four carbon atoms.

a. hex-1-yne

b. hex-2-yne

c. cis-hex-2-ene

Textbook Question

Solved Problem 9-1 showed the synthesis of dec-3-yne by adding the hexyl group first, then the ethyl group. Show the reagents and intermediates involved in the other order of synthesis of dec-3-yne, by adding the ethyl group first and the hexyl group last.

Textbook Question

Acetylide alkylation, from Assessment 12.61, fails to give the desired product with 2° haloalkanes. Why? What is the actual product of this reaction?

Textbook Question

The intended S_N2 displacement of the 1° chloride by acetylide is unsuccessful for the molecule below. Why?

Textbook Question

Show how each of the following compounds can be synthesized from the given starting materials:

a. CH₃CH₂CH₂Br→CH₃CH₂CH₂CH₂CH₃

Textbook Question

How can the following compounds be prepared using ethyne as the starting material?

Textbook Question

How could the following compounds be synthesized from acetylene?

c. CH₃CH═CH₂

Textbook Question

How could the following compounds be synthesized from acetylene?

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Show how the following compounds can be synthesized starting with ethyne:b. trans-3-heptene

Key Concepts

Ethyne as a Building Block

Alkene Synthesis

Stereochemistry of Alkenes

Watch next

Show how the following compounds can be synthesized starting with ethyne:
b. trans-3-heptene