See image — Aromatic Hydrocarbons Chemistry Question

💡 Solution & Explanation

Step 1: Identify each structure in Column I. (a) Cyclobutadiene: a 4-membered ring with 2 double bonds (4 pi electrons, 4n where n=1). It is planar and cyclic with a continuous pi system. (b) Cyclooctatetraene (COT): an 8-membered ring with 4 double bonds (8 pi electrons, 4n where n=2). It is tub-shaped (non-planar), so it does NOT have a continuous pi system. (c) Cyclobutadiene dianion (charge -2): adds 2 electrons to cyclobutadiene's 4 pi electrons = 6 pi electrons (4n+2, n=1). Planar, fully conjugated. (d) Cyclobutadiene dication (charge +2): removes 2 electrons from cyclobutadiene's 4 pi electrons = 2 pi electrons (4n+2, n=0). Planar, fully conjugated. Step 2: Classify each. (a) Cyclobutadiene: 4 pi electrons = 4n (n=1) -> anti-aromatic. Anti-aromatic compounds are highly reactive: they readily react with active metals (p) and readily dimerize at room temperature (q) to escape anti-aromaticity. They have 4n pi electrons (s). Classification: anti-aromatic (x). Matches: p, q, s, x. (b) COT: 8 pi electrons but non-planar (tub shape), so not aromatic or anti-aromatic -> non-aromatic (y). It can react with active metals to form the planar aromatic COT dianion (p). It has 4n pi electrons in count (s) but since it is non-planar, it is non-aromatic. Matches: p, s, y. (c) Cyclobutadiene dianion: 6 pi electrons = 4n+2 (n=1), planar, cyclic, fully conjugated -> aromatic (w). Aromatic compounds have (4n+2) pi electrons (r). The dianion has a high charge density giving it a high dipole moment (z). Matches: r, w, z. (d) Cyclobutadiene dication: 2 pi electrons = 4n+2 (n=0), planar, cyclic, fully conjugated -> aromatic (w). It also satisfies (4n+2) pi electron rule (r). The dication also has high charge giving high dipole (z). Matches: r, w, z. Step 3: Verify against given answer. a -> p, q, s, x: cyclobutadiene is anti-aromatic (x), has 4n pi electrons (s), readily reacts with active metals (p), readily dimerizes (q). Correct. b -> p, s, y: COT is non-aromatic (y), has 8 (=4n) pi electrons (s), reacts with active metals to form dianion (p). Correct. c -> r, w, z: dianion is aromatic (w), 6 pi electrons = 4n+2 (r), high dipole due to -2 charge (z). Correct. d -> r, w, z: dication is aromatic (w), 2 pi electrons = 4n+2 (r), high dipole due to +2 charge (z). Correct. Therefore, the correct answer is a-p,q,s-x; b-p-s-y; c-r-w,z; d-r-w,z.