Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination

Problem 81b

Chapter 12, Problem 81b

A variety of organometallics, which as strong nucleophiles can react with epoxides, are introduced in Chapter 16. Predict the product of these reactions. [Hint: Assume the carbon–metal bond in each is ionic, with the carbon possessing the negative charge.]
(b)

Verified step by step guidance

Identify the organometallic reagent in the reaction. Organometallic compounds typically have a carbon-metal bond, where the carbon is nucleophilic due to its partial negative charge.

Recognize the epoxide as the electrophile in the reaction. Epoxides are three-membered cyclic ethers with significant ring strain, making them highly reactive toward nucleophiles.

Determine the site of nucleophilic attack. The nucleophile (carbon from the organometallic reagent) will attack the less sterically hindered carbon of the epoxide, leading to ring opening. This is due to the SN2-like mechanism of the reaction.

Add a protonation step. After the nucleophilic attack and ring opening, the negatively charged oxygen (from the epoxide) will be protonated by a suitable proton source (e.g., water or an acid) to form the final alcohol product.

Draw the final product. The product will be an alcohol where the nucleophile has added to the less hindered carbon of the epoxide, and the oxygen from the epoxide is now part of a hydroxyl group.

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Key Concepts

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

Organometallic Compounds

Organometallic compounds are molecules that contain a bond between a carbon atom of an organic group and a metal. These compounds are known for their strong nucleophilic properties, allowing them to react with electrophiles, such as epoxides. The metal can vary, influencing the reactivity and stability of the compound.

Epoxide Reactivity

Epoxides are three-membered cyclic ethers that are highly reactive due to the strain in their ring structure. They can undergo nucleophilic attack at the less hindered carbon atom, leading to ring-opening reactions. Understanding the mechanism of this reaction is crucial for predicting the products formed when epoxides react with nucleophiles.

Ionic Carbon-Metal Bond

In the context of organometallics, assuming an ionic carbon-metal bond means that the carbon atom carries a negative charge, making it a strong nucleophile. This assumption simplifies the analysis of the reaction mechanism, as it allows for straightforward predictions about how the nucleophile will interact with the electrophilic epoxide, leading to the formation of specific products.

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Related Practice

Textbook Question

Predict the product of the following epoxide addition reactions.

(b)

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Textbook Question

A variety of organometallics, which as strong nucleophiles can react with epoxides, are introduced in Chapter 16. Predict the product of these reactions. [Hint: Assume the carbon–metal bond in each is ionic, with the carbon possessing the negative charge.]

(c)

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Textbook Question

Show how a protecting group might be used to make these reactions successful.

(a)

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Textbook Question

Reaction of the acetylide with the epoxide shown will not form the desired product. What side reaction occurs instead? Why?

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