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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4:56 minutes

Problem 12d

Textbook Question

Show how you would convert
d. but-1-yne to cis-hex-3-ene.

Verified step by step guidance

Step 1: Begin by identifying the functional group in but-1-yne. It contains a terminal alkyne group (-C≡C-H). The goal is to extend the carbon chain and convert the alkyne into a cis-alkene.

Step 2: Perform a hydroboration reaction to add a boron atom to the terminal alkyne. Use a reagent like disiamylborane (R2BH) to selectively add boron to the terminal carbon. This step prepares the molecule for further functionalization.

Step 3: Oxidize the boron intermediate using hydrogen peroxide (H2O2) in a basic solution (NaOH). This converts the boron group into an alcohol (-OH) at the terminal carbon, resulting in an aldehyde (butanal).

Step 4: Perform a Wittig reaction to extend the carbon chain. React the aldehyde with a phosphonium ylide (Ph3P=CHCH2CH3) to form hex-3-yne. This reaction adds three carbons to the molecule and introduces a triple bond at the desired position.

Step 5: Hydrogenate hex-3-yne using a Lindlar catalyst (Pd/CaCO3, poisoned with quinoline) to selectively reduce the triple bond to a cis-double bond, yielding cis-hex-3-ene as the final product.

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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 reaction known as hydrogenation, where hydrogen gas is added across the triple bond of the alkyne. This process can be facilitated by catalysts such as palladium or platinum, which help to break the triple bond and form a double bond, resulting in an alkene. In this case, but-1-yne will be transformed into an alkene intermediate before further reactions can yield the desired product.

Stereochemistry and Cis-Trans Isomerism

Cis-trans isomerism is a form of stereoisomerism where the spatial arrangement of groups around a double bond affects the properties of the molecule. In cis isomers, similar groups are on the same side of the double bond, while in trans isomers, they are on opposite sides. Understanding this concept is crucial for converting the alkene intermediate into cis-hex-3-ene, as the reaction conditions must favor the formation of the cis isomer.

Reagents for Stereoselective Reactions

To achieve the specific stereochemistry required for cis-hex-3-ene, certain reagents and conditions must be employed. For example, the use of specific catalysts or reagents that promote syn-addition during the hydrogenation process can lead to the formation of the cis isomer. Familiarity with these reagents and their mechanisms is essential for successfully directing the reaction towards the desired stereochemical outcome.

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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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