Q86 · CSIR NET Chemistry, December 2015
Paper: CSIR NET December 2015 · Subject: Organic Chemistry · Chapter: Organic Spectroscopy · Topic: IR · Marks: 2 · Difficulty: Hard
Correctly matched structure and carbonyl stretching frequency set is COLUMN - A 
(P) 
(Q) (R) COLUMN - B (X) $1750$ $\,\mathrm{cm^{-1}}$ (Y) $1770$ $\,\mathrm{cm^{-1}}$ (Z) $1800$ $\,\mathrm{cm^{-1}}$
(P) (Q) (R) COLUMN - B (X) $1750$ $\,\mathrm{cm^{-1}}$ (Y) $1770$ $\,\mathrm{cm^{-1}}$ (Z) $1800$ $\,\mathrm{cm^{-1}}$(a)P-Y, Q-Z, R-X
(b)P-Y, Q-X, R-Z
(c)P-Z, Q-Y, R-X
(d)P-X, Q-Z, R-Y
Answer
Answer: A ✓ checked by 4AB · confidence low
Explanation
The saturated γ-lactone P absorbs at 1770 cm⁻¹. The β,γ-unsaturated enol lactone, with C=C next to the ring O, absorbs highest (≈1800). The conjugated butenolide absorbs lowest (≈1750). Reading Q as the enol lactone gives P-Y, Q-Z, R-X (a).
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