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 48

Chapter 10, Problem 48

Grignard reagents react slowly with oxetane to produce primary alcohols. Propose a mechanism for this reaction, and suggest why oxetane reacts with Grignard reagents even though most ethers do not.

Verified step by step guidance

Step 1: Recognize the reactivity of Grignard reagents. Grignard reagents (R-Mg-X) are highly nucleophilic due to the partial negative charge on the carbon atom bonded to magnesium. This nucleophilicity allows them to attack electrophilic centers in molecules.

Step 2: Analyze the structure of oxetane. Oxetane is a strained four-membered cyclic ether. The ring strain arises due to the small bond angles in the ring, making the oxygen atom more electrophilic and susceptible to nucleophilic attack compared to typical ethers.

Step 3: Propose the mechanism. The Grignard reagent attacks the electrophilic oxygen atom in oxetane, leading to the opening of the strained ring. This results in the formation of a linear alkoxide intermediate.

Step 4: Describe the product formation. After the ring opens, the alkoxide ion (R-CH2CH2CH2-O-) is formed. This is the salt of the primary alcohol, which can be protonated in a subsequent step to yield the primary alcohol.

Step 5: Explain why oxetane reacts with Grignard reagents while most ethers do not. The key difference lies in the ring strain of oxetane. Most ethers lack this strain and are less electrophilic, making them resistant to nucleophilic attack by Grignard reagents.

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Key Concepts

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

Grignard Reagents

Grignard reagents are organomagnesium compounds represented as R-MgX, where R is an organic group and X is a halogen. They are highly reactive nucleophiles that can attack electrophilic centers, such as carbonyl groups, leading to the formation of alcohols. Understanding their reactivity is crucial for predicting the outcomes of reactions involving these reagents.

Oxetane Structure and Reactivity

Oxetane is a four-membered cyclic ether that possesses significant ring strain, making it more reactive than larger ethers. This strain allows oxetane to undergo nucleophilic attack more readily, particularly by Grignard reagents, which can open the ring and lead to the formation of primary alcohols. Recognizing the unique properties of oxetane is essential for understanding its reaction with Grignard reagents.

Mechanism of Nucleophilic Attack

The mechanism of nucleophilic attack involves the donation of an electron pair from the nucleophile (Grignard reagent) to an electrophilic carbon atom, resulting in the formation of a new bond. In the case of oxetane, the ring-opening mechanism leads to the generation of a primary alkoxide intermediate, which can then be protonated to yield the corresponding alcohol. Familiarity with this mechanism is vital for proposing a detailed reaction pathway.

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Related Practice

Textbook Question

Determine the structures of compounds A through G, including stereochemistry where appropriate.

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Textbook Question

Propose structures for intermediates and products (A) through (D)

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Textbook Question

Compound A (C₇H₁₁Br) is treated with magnesium in ether to give B (C₇H₁₁MgBr), which reacts violently with D₂O to give 1-methylcyclohexene with a deuterium atom on the methyl group (C). Reaction of B with acetone (CH₃COCH₃) followed by hydrolysis gives D (C₁₀H₁₈O). Heating D with concentrated H₂SO₄ gives E (C₁₀H₁₆), which decolorizes two equivalents of Br₂ to give F (C₁₀H₁₆Br₄). E undergoes hydrogenation with excess H₂ and a Pt catalyst to give isobutylcyclohexane. Determine the structures of compounds A through F, and show your reasoning throughout.

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Textbook Question

Vinyl alcohols are generally unstable, quickly isomerizing to carbonyl compounds. Propose mechanisms for the following isomerizations.

(c)

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Textbook Question

Vinyl alcohols are generally unstable, quickly isomerizing to carbonyl compounds. Propose mechanisms for the following isomerizations.

(b)

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Many hunting dogs enjoy standing nose-to-nose with a skunk while barking furiously, oblivious to the skunk spray directed toward them. One moderately effective way of lessening the amount of odor is to wash the dog in a bath containing dilute hydrogen peroxide, sodium bicarbonate, and some mild dish detergent. Use chemical reactions to describe how this mixture helps to remove the skunk spray from the dog. The two major components of skunk oil are 3-methylbutane-1-thiol and but-2-ene-1-thiol.

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