For each compound, give the product(s) expected from (1) HgSO4/H2SO4 - catalyzed hydration and (2) hydroboration–oxidation. c. hex-3-yne

Ch.9 - Alkynes

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

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Wade 9th Edition

Ch.9 - Alkynes

Problem 21c

Chapter 9, Problem 21c

For each compound, give the product(s) expected from (1) HgSO₄/H₂SO₄ - catalyzed hydration and (2) hydroboration–oxidation.
c. hex-3-yne

Verified step by step guidance

Step 1: Analyze the structure of hex-3-yne. It is a six-carbon alkyne with a triple bond located between carbons 3 and 4. This is a symmetrical internal alkyne.

Step 2: For HgSO4/H2SO4-catalyzed hydration, the reaction follows Markovnikov's rule. The triple bond undergoes hydration to form an enol intermediate, which tautomerizes to a ketone. The ketone will form at the more substituted carbon of the triple bond.

Step 3: For hydroboration-oxidation, the reaction follows anti-Markovnikov's rule. The triple bond undergoes hydroboration with a bulky borane reagent, followed by oxidation with H2O2/NaOH. This results in the formation of an enol intermediate, which tautomerizes to an aldehyde. The aldehyde will form at the less substituted carbon of the triple bond.

Step 4: Write the expected products for each reaction. For HgSO4/H2SO4-catalyzed hydration, the product will be a ketone. For hydroboration-oxidation, the product will be an aldehyde.

Step 5: Ensure the stereochemistry and regiochemistry of the products are consistent with the reaction mechanisms. Verify that the ketone and aldehyde products are correctly positioned based on Markovnikov and anti-Markovnikov rules.

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Key Concepts

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

Alkyne Hydration

Alkyne hydration involves the addition of water across the triple bond of an alkyne, typically catalyzed by acids like HgSO4 and H2SO4. This reaction leads to the formation of a carbonyl compound, such as a ketone, through a Markovnikov addition mechanism, where the more substituted carbon atom receives the hydroxyl group.

Hydroboration-Oxidation

Hydroboration-oxidation is a two-step reaction that converts alkynes into alcohols. In the first step, borane (BH3) adds to the alkyne in a syn addition, resulting in a trialkylborane intermediate. The second step involves oxidation with hydrogen peroxide and sodium hydroxide, yielding an alcohol with anti-Markovnikov orientation, where the hydroxyl group attaches to the less substituted carbon.

Markovnikov's Rule

Markovnikov's Rule states that in the addition of HX to an alkene or alkyne, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This principle helps predict the outcome of hydration reactions, guiding the formation of more stable carbocation intermediates and influencing the final product distribution in reactions involving unsaturated hydrocarbons.

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Related Practice

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.

1961

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Textbook Question

Predict the product(s) you would expect from treatment of each compound with (1) dilute, neutral KMnO₄ and (2) warm basic KMnO₄, then dilute acid.

(a) hex-1-yne

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Textbook Question

For each compound, give the product(s) expected from (1) HgSO₄/H₂SO₄ - catalyzed hydration and (2) hydroboration–oxidation.

d. cyclodecyne

1424

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Textbook Question

Disiamylborane adds only once to alkynes by virtue of its two bulky secondary isoamyl groups. Disiamylborane is prepared by the reaction of BH₃·THF with an alkene.

a. Draw the structural formulas of the reagents and the products in the preparation of disiamylborane.

b. Explain why the reaction in part (a) goes only as far as the dialkylborane. Why is Sia₃B not formed?

1163

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Textbook Question

For each compound, give the product(s) expected from (1) HgSO₄/H₂SO₄ - catalyzed hydration and (2) hydroboration–oxidation.

b. hex-2-yne

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Textbook Question

For each compound, give the product(s) expected from (1) HgSO₄/H₂SO₄ - catalyzed hydration and (2) hydroboration–oxidation.

a. hex-1-yne

1281

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