Textbook Question
Starting with acetyl chloride, what neutral nucleophile would you use to synthesize each of the following compounds?
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22. Carboxylic Acid Derivatives: NAS
Nucleophilic Acyl Substitution
8:05 minutesProblem 45
Textbook Question
We saw that acid anhydrides react with alcohols, water, and amines. In which of these reactions can the tetrahedral intermediate eliminate the carboxylate ion even if it does not lose a proton before the elimination step? Explain.
Verified step by step guidance1
Step 1: Understand the reaction mechanism of acid anhydrides with alcohols, water, and amines. Acid anhydrides are reactive compounds that undergo nucleophilic acyl substitution reactions. The key intermediate in these reactions is a tetrahedral intermediate formed when the nucleophile attacks the carbonyl carbon.
Step 2: Analyze the elimination step in the reaction mechanism. The tetrahedral intermediate can eliminate a leaving group, such as a carboxylate ion, without losing a proton if the leaving group is already negatively charged. This is because the carboxylate ion is a stable leaving group due to resonance stabilization.
Step 3: Examine the nucleophiles provided in the image: ethanol (CH₃CH₂OH), ethylamine (CH₃CH₂NH₂), and water (H₂O). Ethanol and water are neutral nucleophiles, meaning they will likely lose a proton before elimination occurs. Ethylamine, however, is a basic nucleophile and can form a tetrahedral intermediate where the carboxylate ion is eliminated directly without proton loss.
Step 4: Consider the role of the nucleophile's basicity and the stability of the leaving group. Amines, such as ethylamine, are stronger nucleophiles and can facilitate direct elimination of the carboxylate ion due to their ability to stabilize the intermediate without requiring proton transfer.
Step 5: Conclude that the reaction of acid anhydrides with amines (e.g., CH₃CH₂NH₂) allows the tetrahedral intermediate to eliminate the carboxylate ion directly, even without losing a proton before the elimination step. This is due to the inherent properties of the amine nucleophile and the stability of the carboxylate ion.
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Video duration:
8mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Tetrahedral Intermediate
A tetrahedral intermediate is a transient species formed during nucleophilic acyl substitution reactions, where a nucleophile attacks the carbonyl carbon of a carboxylic acid derivative. This intermediate has a tetrahedral geometry due to the addition of the nucleophile, which temporarily disrupts the carbonyl's planar structure. Understanding this concept is crucial for analyzing how the intermediate can lead to the elimination of leaving groups, such as carboxylate ions.
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04:31
Stability of Conjugated Intermediates
Carboxylate Ion
A carboxylate ion is the conjugate base of a carboxylic acid, formed when the acid loses a proton from its carboxyl group. In the context of acid anhydrides, the carboxylate ion can act as a leaving group during nucleophilic substitution reactions. Recognizing the role of the carboxylate ion is essential for understanding the conditions under which it can be eliminated from the tetrahedral intermediate without prior proton loss.
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Nucleophilic Acyl Substitution
Nucleophilic acyl substitution is a fundamental reaction in organic chemistry where a nucleophile attacks the electrophilic carbon of a carbonyl compound, leading to the substitution of a leaving group. This reaction is characteristic of carboxylic acid derivatives, including acid anhydrides, esters, and amides. Grasping this concept helps in predicting the outcomes of reactions involving acid anhydrides with alcohols, amines, and water, particularly in the context of tetrahedral intermediates.
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01:47Nucleophiles and Electrophiles can react in Substitution Reactions.
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