Ch. 17 - Reactions at the Alpha-Carbon

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 17 - Reactions at the Alpha-Carbon

Problem 61

Chapter 18, Problem 61

Show how 4-methyl-3-hexanol can be synthesized from 3-pentanone.

Verified step by step guidance

Step 1: Begin with the starting material, 3-pentanone. Recognize that the target molecule, 4-methyl-3-hexanol, is an alcohol with a methyl group added to the carbon adjacent to the ketone group in 3-pentanone. This suggests a Grignard reaction as a key step.

Step 2: Prepare the Grignard reagent. React methyl bromide (CH₃Br) with magnesium (Mg) in an ether solvent to form the Grignard reagent, CH₃MgBr. This reagent will act as a nucleophile in the next step.

Step 3: Perform the nucleophilic addition reaction. Add the Grignard reagent (CH₃MgBr) to 3-pentanone. The carbonyl group (C=O) in 3-pentanone will undergo nucleophilic attack by the methyl group from the Grignard reagent, forming a tertiary alkoxide intermediate.

Step 4: Protonate the alkoxide intermediate. Treat the reaction mixture with a dilute acid, such as H₃O⁺, to protonate the alkoxide and form the desired alcohol, 4-methyl-3-hexanol.

Step 5: Verify the structure of the product. Confirm that the product has the correct connectivity and stereochemistry (if applicable) to ensure it matches the target molecule, 4-methyl-3-hexanol.

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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 in organic chemistry where a nucleophile attacks an electrophilic carbon atom, typically in a carbonyl group. In the synthesis of 4-methyl-3-hexanol from 3-pentanone, this reaction is crucial as it allows the introduction of new carbon chains through the addition of nucleophiles, leading to the formation of alcohols.

Grignard Reagents

Grignard reagents are organomagnesium compounds that act as strong nucleophiles in organic synthesis. They can react with carbonyl compounds like ketones to form alcohols. In this synthesis, a Grignard reagent derived from an appropriate alkyl halide can be used to add a methyl group to 3-pentanone, ultimately yielding 4-methyl-3-hexanol.

Reduction Reactions

Reduction reactions involve the gain of electrons or hydrogen, or the loss of oxygen, resulting in the conversion of carbonyl compounds to alcohols. In the context of synthesizing 4-methyl-3-hexanol, the reduction of the intermediate formed after nucleophilic addition is essential to convert the ketone functional group into the desired alcohol, completing the synthesis.

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Related Practice

Textbook Question

Identify A–C. (Hint: A shows three singlets in its 1H NMR spectrum with integral ratios 3 : 2 : 3 and gives a positive iodoform test; see Problem 58.)

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Textbook Question

Using cyclopentanone as the reactant, show the product of

b. an aldol addition.

c. an aldol condensation.

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Textbook Question

There are other condensation reactions similar to the aldol and Claisen condensations:

a. The Perkin condensation is the condensation of an aromatic aldehyde and acetic anhydride. Draw the product obtained from the following Perkin condensation:

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Textbook Question

A β-ɣ-unsaturated carbonyl compound rearranges to a more stable conjugated ⍺,β-unsaturated compound in the presence of either acid or base. b. Propose a mechanism for the acid-catalyzed rearrangement.

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Textbook Question

Show how the following compound can be synthesized from the given starting material. (Hint: Start with an acetoacetic ester.)

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Textbook Question

Using cyclopentanone as the reactant, show the product of a. acid-catalyzed keto–enol interconversion.

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