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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5:12 minutes

Problem 6

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.

Verified step by step guidance

Step 1: Begin by identifying the target molecule, dec-3-yne, which is an alkyne with a triple bond at the third carbon and a hexyl group and ethyl group attached. The goal is to synthesize this molecule by adding the ethyl group first and the hexyl group last.

Step 2: Start with ethyne (C≡CH) as the base molecule. Deprotonate ethyne using a strong base such as sodium amide (NaNH₂) to generate the acetylide ion (C≡C⁻). This ion is highly nucleophilic and will be used for the first substitution reaction.

Step 3: React the acetylide ion with ethyl bromide (CH₃CH₂Br) in an SN2 reaction. The nucleophilic acetylide ion attacks the electrophilic carbon in ethyl bromide, displacing the bromide ion and forming but-1-yne (CH₃CH₂C≡CH). This is the intermediate after the first step.

Step 4: Deprotonate but-1-yne using sodium amide (NaNH₂) again to generate the corresponding acetylide ion (CH₃CH₂C≡C⁻). This prepares the molecule for the second substitution reaction.

Step 5: React the new acetylide ion with hexyl bromide (CH₃(CH₂)₅Br) in another SN2 reaction. The nucleophilic acetylide ion attacks the electrophilic carbon in hexyl bromide, displacing the bromide ion and forming dec-3-yne (CH₃CH₂C≡C(CH₂)₅CH₃). This completes the synthesis with the hexyl group added last.

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Key Concepts

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

Alkyne Synthesis

Alkyne synthesis involves the formation of carbon-carbon triple bonds through various reactions. Common methods include the elimination of hydrogen halides from vicinal or geminal dihalides, or through the coupling of terminal alkynes with alkyl halides using strong bases. Understanding these pathways is crucial for manipulating the order of substituent addition in alkyne synthesis.

Reagents and Intermediates

In organic synthesis, reagents are the substances used to bring about a chemical reaction, while intermediates are transient species formed during the reaction process. Identifying the correct reagents and intermediates is essential for predicting the outcome of a synthesis pathway, especially when altering the order of addition, as it can significantly affect the reaction mechanism and product formation.

Reaction Mechanism

A reaction mechanism describes the step-by-step process by which reactants are converted into products. It includes details about bond breaking and forming, the role of catalysts, and the energy changes involved. Understanding the mechanism is vital for predicting how changing the order of reagent addition will influence the formation of intermediates and the final product in the synthesis of dec-3-yne.

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Related Practice

Textbook Question

Show how you would accomplish the following synthetic transformations. Show all intermediates.

e. 2,2-dibromohexane → hex-1-yne

Textbook Question

How much more stable is the most stable staggered conformer than the most stable eclipsed conformer?

Textbook Question

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

d. trans-hex-2-ene

e. 1,1-dibromohexane

f. 2,2-dibromohexane

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

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 the following compounds can be synthesized starting with ethyne:

b. trans-3-heptene

Textbook Question

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

a. CH₃CH₂CH₂Br→CH₃CH₂CH₂CH₂CH₃

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