JEE Main Chemistry question

Which halo acid gives a cyclic ester on treatment with aq. NaOH?

(A)An α-halo acid (halogen on C adjacent to COOH, forming only a strained 3-membered ring on cyclization — unfavourable)
(B)A β-halo acid (giving a favourable 4-membered β-lactone)
(C)A γ-halo acid (giving a favourable 5-membered γ-lactone)Correct
(D)All of these

Answer: (C)

Solution

Intramolecular SN2 displacement of the halide by the carboxylate oxygen (or via its conjugate base) to form a cyclic ester (lactone) is most favourable when the resulting ring is five- or six-membered. A γ-halo acid, with the halogen three carbons from –COOH, cyclizes readily to a

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Question ID VK-149467