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The cyclopentadienyl anion (C5H5⁻) is a five-membered ring with a negative charge. Is it aromatic, antiaromatic, or non-aromatic?

1. Aromatic
2. Antiaromatic
3. Non-aromatic
4. None of these

Correct answer: Aromatic

Solution

Cyclopentadienyl anion is cyclic, planar, and fully conjugated. It possesses 6 pi electrons (4*1+2 for n=1), satisfying Huckel's rule, and is therefore aromatic.

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