a. Which of the following reactions does not give the carbonyl product shown?
b. Which of the reactions that do not occur can be made to occur if an acid catalyst is added to the reaction mixture?
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Verified step by step guidance

1. Step 1: Analyze the reactions provided in the image. Reaction 1 involves the conversion of an amide to an acyl chloride using Cl⁻. Reaction 2 involves the hydrolysis of an amide to form a carboxylic acid using H₂O. Reaction 3 involves the reaction of an acyl chloride with an enolate to form a β-keto ester.
2. Step 2: Determine which reactions produce the carbonyl product shown. Reaction 1 produces an acyl chloride, Reaction 2 produces a carboxylic acid, and Reaction 3 produces a β-keto ester. Compare these products to the carbonyl product in question.
3. Step 3: Identify the reactions that do not occur under the given conditions. Reaction 2 (amide hydrolysis) typically requires an acid or base catalyst to proceed efficiently. Without a catalyst, this reaction may not occur.
4. Step 4: Consider how the reactions that do not occur can be made to occur. For Reaction 2, adding an acid catalyst (e.g., HCl) would protonate the amide, making it more susceptible to nucleophilic attack by water, thereby facilitating hydrolysis to form the carboxylic acid.
5. Step 5: Summarize the findings. Reaction 2 does not occur without a catalyst but can be made to occur with the addition of an acid catalyst. Reaction 1 and Reaction 3 proceed under the given conditions and produce their respective carbonyl products.

Key Concepts

Nucleophilic Acyl Substitution

Nucleophilic acyl substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks the carbonyl carbon of a carboxylic acid derivative, leading to the substitution of a leaving group. This mechanism is crucial for understanding how different carboxylic acid derivatives, such as esters, amides, and acyl chlorides, react to form carbonyl products. The reaction typically involves the formation of a tetrahedral intermediate, which then collapses to release the leaving group.

Role of Acid Catalysts

Acid catalysts play a significant role in enhancing the reactivity of nucleophilic acyl substitution reactions. They can protonate the carbonyl oxygen, increasing the electrophilicity of the carbonyl carbon, making it more susceptible to nucleophilic attack. This is particularly important in reactions that may not proceed efficiently under neutral conditions, allowing for reactions that would otherwise be unfavorable to occur more readily.

Carboxylic Acid Derivatives

Carboxylic acid derivatives include compounds like acyl chlorides, esters, and amides, which differ in their leaving groups and reactivity. Understanding the structure and reactivity of these derivatives is essential for predicting the outcomes of nucleophilic acyl substitution reactions. Each type of derivative has unique characteristics that influence how they react with nucleophiles and the types of products formed, which is critical for answering questions about specific reaction pathways.