See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Concept: Aromaticity after deprotonation. When a compound is deprotonated at an sp3 carbon, if the resulting anion (or in one case a neutral species) satisfies Hückel's rule (4n+2 pi electrons in a planar, fully conjugated cyclic system), the deprotonated species is stabilized by aromaticity. Step 1 - Analyze each compound upon deprotonation: (a) The compound is a cyclopentadiene derivative with a -CH=C≡N (or =CHCN) exocyclic group at the sp3 carbon of the cyclopentadiene ring. Deprotonation at the sp3 carbon of the 5-membered ring gives a cyclopentadienyl anion. The resulting carbanion has 6 pi electrons in the 5-membered ring (4n+2, n=1), making it aromatic. Additionally, the CN group further stabilizes the negative charge by resonance/induction. This species IS stabilized → YES. (b) Cyclopropene upon deprotonation at the sp3 CH2 gives the cyclopropenyl anion with 4 pi electrons (4n, n=1), which is antiaromatic. This species is DESTABILIZED → NO. (c) Cyclopentadiene (C5H6) has an sp3 CH2 at C5. Deprotonation gives the cyclopentadienyl anion with 6 pi electrons (4n+2, n=1) in a planar 5-membered ring — classically aromatic and very stable. → YES. (d) Cycloheptadiene upon deprotonation at the sp3 carbon gives the cycloheptadienyl anion with 8 pi electrons (4n, n=2), which is antiaromatic. → NO. (e) 2H-pyran upon deprotonation at the sp3 carbon (C2) gives a delocalized anion. The resulting system would have 6 pi electrons over the ring, but the oxygen lone pairs complicate full aromaticity; the pyranyl anion is not classically aromatic in the Hückel sense for a stable aromatic system — it does not achieve the stable aromatic configuration cleanly. → NO. (f) The cyclohexadienyl cation (arenium-like) has a positive charge at an sp3 carbon. Deprotonation removes H from that sp3 carbon, giving benzene (6 pi electrons, 4n+2, n=1), which is the archetypal aromatic compound. This is extremely stabilized. → YES. Step 2 - Count stable species: (a), (c), and (f) → 3 compounds. Step 3 - Why others fail: (b) gives antiaromatic cyclopropenyl anion (4 pi e-); (d) gives antiaromatic cycloheptadienyl anion (8 pi e-); (e) does not yield a classically stable aromatic anion. Therefore, the correct answer is {"count": 3, "items": ["a", "c", "f"]}.