Ch.10 - Structure and Synthesis of Alcohols

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

Wade 9th Edition

Ch.10 - Structure and Synthesis of Alcohols

Problem 16

Chapter 10, Problem 16

Propose a mechanism for the reaction of acetyl chloride with phenylmagnesium bromide to give 1,1-diphenylethanol.

Verified step by step guidance

Step 1: Identify the reactants and the product. Acetyl chloride (CH₃COCl) reacts with phenylmagnesium bromide (C₆H₅MgBr) in an ether solvent, followed by hydrolysis with H₃O⁺, to form 1,1-diphenylethanol.

Step 2: Recognize the role of phenylmagnesium bromide as a Grignard reagent. Grignard reagents are nucleophiles that attack electrophilic carbon atoms, such as the carbonyl carbon in acetyl chloride.

Step 3: The first phenylmagnesium bromide molecule attacks the carbonyl carbon of acetyl chloride, breaking the π bond of the C=O group. This forms a tetrahedral intermediate with a negatively charged oxygen atom and a phenyl group attached to the carbon.

Step 4: The chloride ion (Cl⁻) leaves as a good leaving group, resulting in the formation of a ketone intermediate, acetophenone (C₆H₅COCH₃).

Step 5: The second phenylmagnesium bromide molecule attacks the carbonyl carbon of the ketone intermediate, forming another tetrahedral intermediate. Upon hydrolysis with H₃O⁺, the negatively charged oxygen is protonated, yielding the final product, 1,1-diphenylethanol.

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Key Concepts

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

Nucleophilic Addition

Nucleophilic addition is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks an electrophilic carbon atom, leading to the formation of a new bond. In this case, phenylmagnesium bromide acts as a nucleophile, attacking the carbonyl carbon of acetyl chloride, which is an electrophile due to the polarization of the carbon-oxygen double bond.

Grignard Reagents

Grignard reagents, such as phenylmagnesium bromide, are organomagnesium compounds that are highly reactive and serve as strong nucleophiles. They can react with various electrophiles, including carbonyl compounds, to form alcohols. Understanding their reactivity is crucial for predicting the outcome of reactions involving these reagents.

Protonation of Alkoxide

After the nucleophilic addition of phenylmagnesium bromide to acetyl chloride, an alkoxide intermediate is formed. This intermediate is then protonated, typically by adding water or an acid, to yield the final alcohol product, 1,1-diphenylethanol. This step is essential for converting the alkoxide into a stable alcohol.

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Related Practice

Textbook Question

Show how you would add Grignard reagent to acid chloride or ester to synthesize the following alcohols.

a. Ph₃C–OH

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Textbook Question

Show how you would synthesize following tertiary alcohol by adding an appropriate Grignard reagent to a ketone.

c. 1-ethylcyclopentanol

530

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Textbook Question

Show how you would synthesize following tertiary alcohol by adding an appropriate Grignard reagent to a ketone.

b. Ph₃COH

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Textbook Question

A formate ester, such as ethyl formate, reacts with an excess of a Grignard reagent to give (after protonation) secondary alcohols with two identical alkyl groups.

(a) Propose a mechanism to show how the reaction of ethyl formate with an excess of allylmagnesium bromide gives, after protonation, hepta-1,6-dien-4-ol.

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Textbook Question

Show how you would add Grignard reagent to acid chloride or ester to synthesize the following alcohols.

c. dicyclohexylphenylmethanol

612

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Textbook Question

Show how you would synthesize following tertiary alcohol by adding an appropriate Grignard reagent to a ketone.

d. 2-cyclopentylpentan-2-ol

594

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