See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Ease of ionization under acidic conditions refers to the ease of carbocation (oxocarbenium/carbenium) formation upon protonation and loss of water — i.e., the stability of the resulting carbocation. Step 1 — Identify the carbocation formed upon ionization of each alcohol: • Compound I (9-fluorenol): loss of OH gives the 9-fluorenyl cation. The five-membered ring carbocation is flanked by two benzene rings; however, the geometry of fluorene forces the empty p-orbital to be perpendicular to both aromatic π-systems, giving poor conjugation. The 9-fluorenyl cation is actually destabilized relative to a simple benzylic cation because the two aryl groups are locked in a geometry where the p-orbital at C9 cannot overlap effectively with both arenes simultaneously (bridged, rigid planar system). The fluorenyl cation is antiaromatic (cyclopentadienyl cation character — 4π electrons in the five-membered ring), making it highly unstable. • Compound II (xanthen-9-ol): loss of OH gives the xanthenyl cation (xanthylium cation). The oxygen atom of the pyran ring is directly conjugated with the empty carbocation center at C9, providing powerful lone-pair donation (oxocarbenium stabilization), plus additional delocalization into both flanking benzene rings. The xanthylium cation is exceptionally stable — it is a well-known, isolable, highly colored cation. This gives compound II the greatest ease of ionization. • Compound III (dibenzosuberol): loss of OH gives the dibenzosuberyl (5-dibenzo[a,d]cycloheptenyl) cation. The seven-membered ring allows the two benzene rings to adopt a geometry where the empty p-orbital at C5 can conjugate with both arenes. The carbocation is stabilized by homoaromatic/bishomoarene overlap and normal bis-benzylic conjugation. It is more stable than the fluorenyl cation (no antiaromaticity) but less stable than the xanthylium cation (no heteroatom lone-pair donation). Step 2 — Rank the carbocation stabilities (= ease of ionization): Xanthylium (II) > Dibenzosuberyl (III) > Fluorenyl (I) • II is most stable due to oxygen lone-pair donation (oxocarbenium) + extended conjugation. • III is intermediate: bis-benzylic stabilization, flexible geometry, no destabilizing antiaromaticity. • I is least stable: the 9-fluorenyl cation is antiaromatic (4n π, n=1, in the five-membered ring), making ionization most difficult. Step 3 — Match to answer choices: Decreasing order of ease of ionization: II > III > I → option (c). Why other options fail: (a) I > III > II — wrong; places the antiaromatic fluorenyl cation as most stable, which is incorrect. (b) I > II > III — same error, also ignores oxocarbenium stabilization of II. (d) II > I > III — wrong order for I and III; fluorenyl cation is less stable than dibenzosuberyl cation. Therefore, the correct answer is C.