Textbook Question
A student provided the product of the following reactions, but made a mistake. Identify the mistake, correct the mistake, and suggest a way for the student to avoid that mistake in the future.
(a)
9. Alkenes and Alkynes
Acetylide
1:53 minutesProblem 20a
Textbook Question
Suggest an acetylide ion and a carbonyl that might be used to make the following products.
(a) oct-4-yn-3-ol
Verified step by step guidance1
Step 1: Recognize the structure of the target molecule, oct-4-yn-3-ol. It contains an alkyne group (triple bond) at position 4 and a hydroxyl group (-OH) at position 3. This suggests that the molecule can be synthesized via the reaction of an acetylide ion with a carbonyl compound, followed by protonation.
Step 2: Identify the acetylide ion. The alkyne group in the product indicates that the acetylide ion should have a terminal alkyne. To form the carbon chain leading to oct-4-yn-3-ol, the acetylide ion should be derived from 1-butyne (CH≡C-CH2CH3). The acetylide ion is formed by deprotonating 1-butyne with a strong base, such as sodium amide (NaNH2), resulting in CH≡C⁻CH2CH3.
Step 3: Determine the carbonyl compound. The hydroxyl group at position 3 in the product suggests that the carbonyl compound should be a ketone. The reaction of the acetylide ion with the carbonyl compound will form a new carbon-carbon bond. To achieve the correct structure, the carbonyl compound should be propanone (CH3COCH3).
Step 4: Outline the reaction mechanism. The acetylide ion (CH≡C⁻CH2CH3) acts as a nucleophile and attacks the electrophilic carbon of the carbonyl group in propanone (CH3COCH3). This forms an alkoxide intermediate.
Step 5: Protonate the alkoxide intermediate. The alkoxide ion formed in the previous step is protonated using a proton source, such as water (H2O) or a dilute acid, to yield the final product, oct-4-yn-3-ol.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acetylide Ion
An acetylide ion is a negatively charged species formed by deprotonating a terminal alkyne. It is a strong nucleophile, capable of attacking electrophiles such as carbonyl compounds. In organic synthesis, acetylide ions are often used to form carbon-carbon bonds, making them essential for constructing complex molecules.
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Carbonyl Compounds
Carbonyl compounds contain a carbon atom double-bonded to an oxygen atom, and they include aldehydes, ketones, and carboxylic acids. They are key intermediates in organic reactions, particularly in nucleophilic addition reactions where nucleophiles, like acetylide ions, can attack the electrophilic carbon of the carbonyl. Understanding the reactivity of carbonyls is crucial for predicting the outcomes of synthetic pathways.
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Nucleophilic Addition
Nucleophilic addition is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks an electrophilic carbon atom, typically in carbonyl compounds. This reaction leads to the formation of a new carbon-carbon or carbon-heteroatom bond. In the context of synthesizing oct-4-yn-3-ol, the nucleophilic addition of an acetylide ion to a carbonyl compound is a critical step in constructing the desired product.
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