JEE Main Chemistry question

Give the order of ease of decarboxylation of the following acids: CH₃COOH (I); CH₂=CH–CH₂COOH (II); CH₂(COOH)₂ (malonic acid, III); 2,4-dinitrobenzoic acid (IV).

(A)I > II > III > IV
(B)III > IV > II > ICorrect
(C)IV > III > II > I
(D)I > III > II > IV

Answer: (B)

Solution

Decarboxylation is facilitated by features that stabilize the developing negative charge/carbanion-like transition state at the carbon losing CO₂: a second carbonyl group adjacent (as in malonic acid, a 1,3-dicarbonyl-type system enabling a cyclic transition state, III) gives by far the easiest decarboxylation;

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Question ID VK-149509