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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4:16 minutes

Problem 35a,b

Textbook Question

Show how you would synthesize the following compounds from acetylene and any other needed reagents:
(a) 6-phenylhex-1-en-4-yne
(b) cis-1-phenylpent-2-ene

Verified step by step guidance

Step 1: Begin with acetylene (C₂H₂) as the starting material. To elongate the carbon chain, perform an alkylation reaction. First, deprotonate acetylene using a strong base like sodium amide (NaNH₂) to generate the acetylide ion. Then, react the acetylide ion with an appropriate alkyl halide (e.g., 1-bromobutane for part (a) and 1-bromopropane for part (b)) to add the desired carbon chain.

Step 2: For part (a), introduce the phenyl group. Use a second alkylation step by deprotonating the terminal alkyne again with NaNH₂ and reacting it with benzyl bromide (C₆H₅CH₂Br). This will attach the phenyl group to the chain. For part (b), the phenyl group can be introduced similarly, but ensure the chain length matches the target compound.

Step 3: To create the double bond in part (b), perform a partial hydrogenation of the alkyne using a Lindlar catalyst (Pd/CaCO₃, poisoned with quinoline). This will selectively reduce the alkyne to a cis-alkene. For part (a), retain the triple bond in the structure as required.

Step 4: For part (a), adjust the position of the triple bond and double bond as needed. Use hydroboration-oxidation (BH₃ followed by H₂O₂/NaOH) to convert the terminal alkyne into an alkene. Ensure the double bond is positioned correctly in the hex-1-en-4-yne structure.

Step 5: Verify the stereochemistry and connectivity of the final products. For part (b), ensure the cis configuration of the alkene is preserved. For part (a), confirm the phenyl group and the triple bond are correctly positioned in the 6-phenylhex-1-en-4-yne structure.

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Key Concepts

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

Alkyne Synthesis

Alkynes are hydrocarbons containing at least one carbon-carbon triple bond. They can be synthesized from simpler compounds like acetylene through various reactions, including elimination and coupling reactions. Understanding the mechanisms of these reactions is crucial for constructing more complex alkynes from simpler starting materials.

Electrophilic Addition Reactions

Electrophilic addition reactions involve the addition of electrophiles to nucleophilic sites in alkenes and alkynes. This concept is essential for synthesizing compounds like cis-1-phenylpent-2-ene, where the orientation of the addition can lead to different stereoisomers. Recognizing how to control regioselectivity and stereochemistry is vital in organic synthesis.

Reagents and Reaction Conditions

The choice of reagents and reaction conditions significantly influences the outcome of organic reactions. For synthesizing the specified compounds, reagents such as bromine, lithium diisopropylamide (LDA), or Grignard reagents may be required. Understanding how these reagents interact with acetylene and other substrates is key to achieving the desired products.

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For each of the following target molecules, design a multistep synthesis to show how it can be prepared from the given starting material:

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Beginning with acetylene and benzyl bromide and using any other inorganic reagents, propose a synthesis of the alkene shown here.

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Show how you would synthesize the following compounds from acetylene and any other needed reagents:(a) 6-phenylhex-1-en-4-yne(b) cis-1-phenylpent-2-ene

Key Concepts

Alkyne Synthesis

Electrophilic Addition Reactions

Reagents and Reaction Conditions

Watch next

Show how you would synthesize the following compounds from acetylene and any other needed reagents:
(a) 6-phenylhex-1-en-4-yne
(b) cis-1-phenylpent-2-ene