Ch.8 - Reactions of Alkenes

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

Wade 9th Edition

Ch.8 - Reactions of Alkenes

Problem 55b,c,d

Chapter 8, Problem 55b,c,d

Complete each synthesis by providing the structure of the major product at each step, including any important stereochemistry.
b.
c.
d.

Verified step by step guidance

Step 1: Analyze the reaction sequence for part b. The first step involves oxymercuration-demercuration using Hg(OAc)₂, H₂O, and NaBH₄. This reaction adds water across the double bond in a Markovnikov fashion, forming an alcohol as the major product.

Step 2: The second step in part b involves acid-catalyzed dehydration using H₂SO₄. This converts the alcohol into an alkene via elimination, forming the more substituted alkene as the major product.

Step 3: The third step in part b involves dihydroxylation using OsO₄ and H₂O₂. This reaction adds two hydroxyl groups to the alkene in a syn fashion, forming a vicinal diol.

Step 4: For part c, the first step involves radical addition of HBr in the presence of ROOR. This reaction adds HBr to the double bond in an anti-Markovnikov fashion, forming a brominated product.

Step 5: The second step in part c involves elimination using KO-t-Bu and heat. This reaction removes HBr, forming an alkyne. Subsequent ozonolysis with O₃ and (CH₃)₂S cleaves the triple bond, forming carboxylic acids or ketones depending on the structure.

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Key Concepts

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

Hydration of Alkenes

The hydration of alkenes involves the addition of water across a double bond, typically catalyzed by acids. In this reaction, the alkene is converted into an alcohol. The mechanism often follows Markovnikov's rule, where the more substituted carbon atom receives the hydroxyl group, leading to the formation of a more stable carbocation intermediate.

Reduction Reactions

Reduction reactions in organic chemistry refer to the gain of electrons or hydrogen, or the loss of oxygen. In the context of the provided synthesis, sodium borohydride (NaBH4) is used to reduce the carbonyl compound formed during hydration to an alcohol. This step is crucial for converting the intermediate product into a more stable and functionalized alcohol.

Dihydroxylation

Dihydroxylation is the addition of two hydroxyl groups (-OH) to a double bond, resulting in a vicinal diol. The reaction can be achieved using osmium tetroxide (OsO4) in the presence of hydrogen peroxide (H2O2), which provides a syn addition mechanism. This step is important for introducing stereochemistry into the product, as it can lead to specific configurations in the final compound.

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General properties of syn vicinal dihydroxylation.

Related Practice

Textbook Question

Professor Patrick Dussault (University of Nebraska at Lincoln) has developed an alternative to the standard two-step ozonolysis procedure requiring reduction of the ozonide in a second step. He uses 2 to 3 equivalents of pyridine, a mildly basic organic solvent, in a one-step process (Organic Letters, 2012, 14, 2242). Show the products you expect from the following examples.

(c)

(d)

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Textbook Question

Complete each synthesis by providing the structure of the major product at each step, including any important stereochemistry.

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Textbook Question

Propose mechanisms consistent with the following reactions.

(c)

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Textbook Question

Following the instructions for drawing the energy levels of the molecular orbitals for the compounds shown in [Figure 8.17], draw the energy levels of the molecular orbitals for the cycloheptatrienyl cation. For each compound, show the distribution of the $\pi$ electrons. Which of the compounds are aromatic?

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Textbook Question

Propose mechanisms consistent with the following reactions.

(b)

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Textbook Question

Propose mechanisms consistent with the following reactions.

(a)

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