Which diccarboxylic acid in presence of a dehydrating agent is least reactive to give anhydride?
(A)(see structure)✓ Correct
(B)(see structure)
(C)(see structure)
(D)(see structure)
Answer: (A)
Solution
Anhydride formation from a dicarboxylic acid is intramolecular: the two carboxyl groups must curl round and close a ring, and that closure is easy only when it makes a five- or six-membered ring. The acid that would have to form a seven-membered anhydride ring is the reluctant one, since the larger ring is strained and costly to assemble. The six-carbon diacid shown is exactly that case, so it is the least reactive toward anhydride formation, while the others close comfortably into five- or six-membered anhydrides.
JEE Main · 2019 · 10 Jan 2019 · Shift 1 · Single correct option
