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

10. Addition Reactions

Alkyne Hydroboration

Organic Chemistry

10. Addition Reactions

Alkyne Hydroboration

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6:04 minutes

Problem 38

Textbook Question

Draw the ketone(s) you would expect to form by treating the following alkynes under the conditions of hydroboration–oxidation: (a) 6-methyloct-1-yne, (b) 1,10-dicyclohexyldec-5-yne, and (c) 5-phenylhex-2-yne.
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Verified step by step guidance

Step 1: Understand the reaction mechanism. Hydroboration–oxidation of alkynes involves the addition of borane (BH₃) to the triple bond, followed by oxidation with hydrogen peroxide (H₂O₂) in the presence of sodium hydroxide (NaOH). This reaction converts the alkyne into a ketone via anti-Markovnikov addition.

Step 2: Analyze the structure of the alkyne. For each alkyne provided, identify the triple bond and determine the regioselectivity of the reaction. Hydroboration–oxidation typically results in the formation of a ketone at the less substituted carbon of the triple bond.

Step 3: For (a) 6-methyloct-1-yne, locate the triple bond between carbons 1 and 2. The hydroboration–oxidation will yield a ketone at the terminal carbon (C1), as it is less substituted. Draw the resulting ketone structure.

Step 4: For (b) 1,10-dicyclohexyldec-5-yne, locate the triple bond between carbons 5 and 6. The hydroboration–oxidation will yield a ketone at carbon 5, as it is less substituted compared to carbon 6. Draw the resulting ketone structure.

Step 5: For (c) 5-phenylhex-2-yne, locate the triple bond between carbons 2 and 3. The hydroboration–oxidation will yield a ketone at carbon 2, as it is less substituted compared to carbon 3. Draw the resulting ketone structure.

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Key Concepts

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

Hydroboration-Oxidation

Hydroboration-oxidation is a two-step reaction process used to convert alkynes into carbonyl compounds, specifically ketones or aldehydes. In the first step, borane (BH₃) adds across the triple bond of the alkyne, forming a trialkylborane intermediate. The second step involves oxidation with hydrogen peroxide (H₂O₂) and a base (NaOH), which converts the boron atom into a hydroxyl group, yielding the corresponding ketone or aldehyde.

Alkyne Reactivity

Alkynes are hydrocarbons containing a carbon-carbon triple bond, which makes them highly reactive. Their reactivity allows them to undergo various addition reactions, including hydroboration. The position of the triple bond and the substituents on the alkyne influence the regioselectivity of the reaction, determining whether a ketone or aldehyde is formed after oxidation.

Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In the context of hydroboration-oxidation of alkynes, the regioselectivity is influenced by the sterics and electronics of the substituents on the alkyne. This concept is crucial for predicting the specific ketone products formed from the given alkynes in the question.

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Textbook Question

The hydroboration–oxidation of internal alkynes produces ketones.

b. When hydroboration–oxidation is applied to pent-2-yne, two products are obtained. Show why a mixture of products should be expected with any unsymmetrical internal alkyne.

Textbook Question

The hydroboration–oxidation of internal alkynes produces ketones.

a. When hydroboration–oxidation is applied to but-2-yne, a single pure product is obtained. Determine the structure of this product, and show the intermediates in its formation.

Textbook Question

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

j. trans-hex-2-ene → cis-hex-2-ene

Textbook Question

Predict the products of reaction of pent-1-yne with the following reagents.

j. NaNH₂

k. H₂SO₄/HgSO₄, H₂O

l. Sia₂BH, then H₂O₂, ^–OH

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (vii) 1. BH₃ 2. H₂O₂, NaOH. If you expect two products, show both.

(c)

Textbook Question

Predict the product of the following aldehyde/ketone syntheses.

(c)

Textbook Question

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

Textbook Question

What are products of the following reactions?

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