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Which of the following reactions or products is correctly paired with its aromaticity or non-aromaticity?

1. Benzene reacted with excess Cl2 under UV light at 500 K gives hexachlorocyclohexane, which is non-aromatic.
2. 2-Bromobutane treated first with alcoholic KOH then NaNH2 gives propyne (CH3-C≡CH), which on passing over red-hot iron at 873 K gives mesitylene — an aromatic compound.
3. Bromocyclobutene reacted with NaOEt gives a substitution product (non-aromatic) and an elimination product that dimerizes to a non-aromatic compound.
4. Cyclopentadiene reacted with NaOMe gives sodium cyclopentadienide (aromatic anion) and methanol.

Correct answer: Cyclopentadiene reacted with NaOMe gives sodium cyclopentadienide (aromatic anion) and methanol.

Solution

Option D is correct: cyclopentadiene is deprotonated by NaOMe to give the cyclopentadienyl anion (6 pi electrons, aromatic). Option B is also correct in its chemistry and aromaticity claim. Option A is correct (hexachlorocyclohexane is non-aromatic). Option C is questionable regarding the dimer being non-aromatic. D is the most clearly correct and unambiguous.

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