See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: Resonance energy (delocalization energy) increases with (1) greater extent of conjugation (more overlapping p orbitals) and (2) lone-pair donors (like -OCH3) conjugated into the pi system. Step 1 – Analyze Compound (III): vinyl methyl ether (CH2=CH-OCH3). This has one C=C double bond conjugated with the lone pair on oxygen. There is only one pi bond involved in conjugation. Resonance structures: CH2=CH-OCH3 <-> -CH2-CH=O+CH3. Resonance energy is small because there is only one double bond interacting with oxygen. Step 2 – Analyze Compound (II): The structure shows a 1,3-diene unit (CH2=CH-CH=C-) with an exo-methylene and an OCH3 directly on the sp2 carbon of the cross-conjugated or cumulated system. Looking carefully at the image, compound (II) is CH2=CH-CH=C(OCH3)-CH=CH2 or more precisely a system where OCH3 is on a carbon that is part of a diene. The OCH3 lone pair can conjugate into the diene pi system. This gives more resonance contributors than III, but the conjugation pathway is interrupted or branched (cross-conjugated at the sp2 carbon bearing OCH3 and the exo-methylene), limiting full delocalization. Resonance energy is intermediate. Step 3 – Analyze Compound (I): CH2=CH-CH=CH-CH=CH-OCH3, a fully conjugated triene (three alternating double bonds) terminating in an enol ether (-CH=CH-OCH3). All three double bonds are in conjugation with each other AND with the lone pair on oxygen. This linear, fully conjugated system allows maximum delocalization across all pi bonds and the oxygen lone pair, giving the highest resonance energy of the three. Step 4 – Ordering: - (I) has 3 conjugated double bonds + O lone pair -> highest resonance energy - (II) has 2 double bonds + O lone pair but cross/branched conjugation -> intermediate - (III) has 1 double bond + O lone pair -> lowest resonance energy Order: I > II > III Why other options fail: - (a) III > I > II: Incorrect; III has fewest conjugated bonds so cannot be highest. - (b) II > I > III: Incorrect; I has more extended conjugation than II. - (d) III > II > I: Incorrect for same reason as (a). Therefore, the correct answer is C.