The order of relative stability of the contributing structure is:
Choose the correct answer from the options given below:
(A)I > II > III✓ Correct
(B)II > I > III
(C)I = II = III
(D)III > II > I
Answer: (A)
Solution
These are resonance contributors of an α,β-unsaturated carbonyl system. Structure I is a neutral resonance form with no formal charges. Structures II and III separate charge — a hallmark of higher-energy, less-favourable contributors, so both are less stable than I.
Between the two charge-separated forms, the one that places the negative charge on the more electronegative atom is favoured: a form with negative charge on oxygen is more stable than one with negative charge on carbon (with the compensating positive charge then sitting on oxygen). Applying this, structure II carries the negative charge on the more electronegative oxygen and is therefore more stable than structure III, which places the positive charge on oxygen instead.
The overall stability order is I > II > III.
JEE Main · 2024 · 27 Jan 2024 · Shift 2 · Single correct option
