IIT-JEE 2012 · Paper 2 · Chemistry Q26

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ChemistrySingle correct+3 / -1Question 26 of 60

The compound that undergoes decarboxylation most readily under mild condition is

2-(Carboxymethyl)cyclohexane-1-carboxylic acid: a cyclohexane with COOH and, on the adjacent carbon, CH₂COOH.

2-Oxocyclohexane-1-carboxylic acid (a β-keto acid).

2-Oxocyclohexylacetic acid (a γ-keto acid): CH₂COOH on the carbon next to the ring C=O.

Answer and worked solution

Official answer: B

β-Keto acids decarboxylate easily on mild warming, through a six-membered cyclic transition state in which the ketone oxygen takes the carboxyl hydrogen, giving an enol and $\ce{CO2}$ .

(B), 2-oxocyclohexanecarboxylic acid, is a β-keto acid.
(A) and (C) are simple dicarboxylic acids (1,4- and 1,2-related), and (D) is a γ-keto acid: none has the β-carbonyl needed for the cyclic mechanism.

(B)

Topics:Carboxylic acids

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IIT-JEE 2012 · Paper 2, Chemistry question 26