Compound 1, a carboxylic acid derivative, cannot undergo decarboxylation because the carboxylic acid derivative:

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11ecba2d_12b4_4015_a3bf_7985c82c5ab4_MD0008_00 Decarboxylation is a reaction that removes a carboxyl group from a carboxylic acid with a β-carbonyl, releasing the carboxyl group as CO₂ gas. An ester with a β-carbonyl can also undergo decarboxylation if the ester is first hydrolyzed to a carboxylic acid. Once the carboxylic acid is formed, decarboxylation occurs through a cyclic transition state that incorporates both carbonyls, releases CO₂, and forms an enol. The enol tautomerizes to the keto form, or the α-carbon can be alkylated and form a ketone. Compound 1, a carboxylic acid derivative, is the ester ethyl hexanoate, which does not contain a β-carbonyl. Therefore, the ester cannot undergo decarboxylation. (Choice B) The carboxylic acid derivative is an ester, but it is not conjugated. In addition, conjugation is not required for decarboxylation. (Choice C) A β-carbonyl is required for decarboxylation, but a carboxyl group is also necessary. A β-diketone, a functional group made up of two carbonyls separated by a CH₂, cannot undergo decarboxylation because it does not contain a carboxyl group. (Choice D) Esters do contain an acidic proton (α-hydrogen), but acidic protons do not take part in the decarboxylation mechanism. Educational objective: Decarboxylation is a reaction that removes a carboxyl group from a carboxylic acid with a β-carbonyl, releasing the carboxyl group as CO₂ gas. A β-carbonyl is necessary for decarboxylation because a cyclic transition state incorporating both carbonyls is formed. Esters with a β-carbonyl can also undergo decarboxylation if they are hydrolyzed to a carboxylic acid first.

Compound 1, a Carboxylic Acid Derivative, Cannot Undergo Decarboxylation Because