See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: 4-Pyrone is a cyclic compound with an oxygen in the ring and a carbonyl group at the 4-position. When it reacts with a proton (acid), the most stable cationic product arises from protonation at the site that gives maximum resonance stabilization. Step 1 - Identify the basic sites in 4-pyrone: 4-Pyrone has two oxygen atoms - the ring oxygen (position 1) and the carbonyl oxygen (position 4). Protonation can occur at either oxygen. Step 2 - Consider protonation at the carbonyl oxygen (position 4): If the carbonyl oxygen is protonated (C=O becomes C-OH with positive charge on oxygen), the resulting cation can delocalize the positive charge. The resonance structure would show the ring oxygen donating electrons into the ring, generating a fully conjugated 6π-electron aromatic system. The structure becomes: O+ (ring oxygen with H... wait, let me reconsider. Step 3 - Reconsidering: Protonation at the ring oxygen gives O+-H in the ring. But protonation at the carbonyl oxygen gives C=O+H, which via resonance becomes C+-OH, and then the ring oxygen lone pair can donate to give a fully aromatic pyrylium-like cation with 6 π electrons (the 4H-pyran-4-one protonated at carbonyl oxygen gives a hydroxypyrylium cation). Step 4 - The hydroxypyrylium cation: When the carbonyl oxygen of 4-pyrone is protonated, the resulting species [4-hydroxypyrylium] has the structure: ring oxygen at position 1, C=C double bonds at 2,3 and 5,6 positions, and C-OH+ at position 4. The ring oxygen lone pair contributes to make a 6π aromatic system analogous to pyrylium. This gives exceptional stability. Step 5 - Matching to option (c): Option (c) shows a six-membered ring with oxygen at position 1 (ring O, neutral), a fully conjugated diene system (double bonds at C2-C3 and C5-C6), and the exocyclic oxygen at position 4 bearing a positive charge with an H attached (O+-H). This corresponds to protonation at the carbonyl oxygen, giving the hydroxypyrylium cation - a stable 6π aromatic species. Step 6 - Why other options fail: - Option (a): Shows protonation at the ring oxygen and disruption of conjugation (sp3 carbon present), losing aromaticity - not the most stable product. - Option (b): Shows protonation at a ring carbon, breaking conjugation - highly unstable, not preferred. - Option (d): Shows protonation at the ring oxygen (O+-H in ring) with full conjugation. While this would give a pyrylium-type cation, the positive charge on the ring oxygen is less stable than the hydroxypyrylium where protonation is at carbonyl oxygen giving delocalized charge through the ring with the ring O donating electrons. The most stable cationic product is the hydroxypyrylium cation formed by protonation at the carbonyl oxygen, which is shown in option (c). Therefore, the correct answer is C.