Ch. 14 - Ethers, Epoxides, and Thioethers

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

Wade 9th Edition

Ch. 14 - Ethers, Epoxides, and Thioethers

Problem 24a

Chapter 14, Problem 24a

Show the rest of the mechanism for formation of the cyclized intermediate in Figure 14-6.

Verified step by step guidance

Step 1: Identify the functional groups involved in the cyclization reaction. Look for nucleophilic and electrophilic centers in the molecule depicted in Figure 14-6. Typically, a nucleophile (such as an alcohol or amine group) will attack an electrophilic center (such as a carbonyl carbon or an alkene).

Step 2: Determine the type of reaction mechanism that leads to cyclization. Common mechanisms include nucleophilic addition, nucleophilic substitution, or electrophilic addition. For example, if a carbonyl group is involved, the mechanism might proceed through nucleophilic attack on the carbonyl carbon.

Step 3: Draw the first step of the mechanism, showing the movement of electrons. Use curved arrows to indicate how the nucleophile attacks the electrophile, forming a new bond. Ensure that you account for any proton transfers or intermediate species that may form during this step.

Step 4: Continue the mechanism by showing subsequent steps that lead to the formation of the cyclized intermediate. This may involve additional bond formation, proton transfers, or rearrangements. Be sure to check for stereochemistry if applicable.

Step 5: Verify the structure of the cyclized intermediate. Ensure that all atoms have the correct valency, and confirm that the intermediate is consistent with the reaction conditions and the overall mechanism described in Figure 14-6.

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Key Concepts

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

Cyclization Mechanism

Cyclization refers to the process where a linear or branched chain molecule forms a cyclic structure. This often involves the formation of new bonds, typically through nucleophilic attack or electrophilic addition, leading to the closure of a ring. Understanding the specific steps and intermediates involved in cyclization is crucial for predicting the outcome of reactions in organic chemistry.

Reaction Intermediates

Reaction intermediates are transient species that form during the conversion of reactants to products. They are often unstable and exist only for a short duration. Identifying these intermediates is essential for understanding the mechanism of a reaction, as they can provide insight into the pathway and energy changes involved in the cyclization process.

Mechanistic Pathways

Mechanistic pathways describe the step-by-step sequence of elementary reactions that occur during a chemical transformation. Each step involves specific bond-breaking and bond-forming events, which can be influenced by factors such as sterics and electronics. A clear understanding of these pathways is necessary to elucidate how the cyclized intermediate is formed and to predict the behavior of similar reactions.

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Related Practice

Textbook Question

Predict the major products of the following reactions, including stereochemistry where appropriate.

a. 2,2-dimethylxirane + H⁺/H₂¹⁸O (oxygen labeled water)

b. 2,2-dimethylxirane + H¹⁸O^–/H₂¹⁸O (oxygen labeled water)

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Textbook Question

Propose mechanisms for the epoxidation and ring-opening steps of the epoxidation and hydrolysis of trans-but-2-ene shown above. Predict the product of the same reaction with cis-but-2-ene.

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Textbook Question

The 2001 Nobel Prize in Chemistry was awarded to three organic chemists who have developed methods for catalytic asymmetric syntheses. An asymmetric (or enantioselective) synthesis is one that converts an achiral starting material into mostly one enantiomer of a chiral product. K. Barry Sharpless (The Scripps Research Institute) developed an asymmetric epoxidation of allylic alcohols that gives excellent chemical yields and greater than 90% enantiomeric excess.

The Sharpless epoxidation uses tert-butyl hydroperoxide, titanium(IV) isopropoxide, and a dialkyl tartrate ester as the reagents. The following epoxidation of geraniol is typical.

(a) Which of these reagents is most likely to be the actual oxidizing agent? That is, which reagent is reduced in the reaction? What is the likely function of the other reagents?

(b) When achiral reagents react to give a chiral product, that product is normally formed as a racemic mixture of enantiomers. How can the Sharpless epoxidation give just one nearly pure enantiomer of the product?

(c) Draw the other enantiomer of the product. What reagents would you use if you wanted to epoxidize geraniol to give this other enantiomer?

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Textbook Question

Predict the major product when each reagent reacts with ethylene oxide.

(a) NaOCH₂CH₃ (sodium ethoxide)

(b) NaNH₂ (sodium amide)

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Textbook Question

Cellosolve® is the trade name for 2-ethoxyethanol, a common industrial solvent. This compound is produced in chemical plants that use ethylene as their only organic feedstock. Show how you would accomplish this industrial process.

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Textbook Question

Predict the major product when each reagent reacts with ethylene oxide.

(d) PhNH₂ (aniline)

(e) KCN (potassium cyanide)

(f) NaN₃ (sodium azide)

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