Which of the two: cyclopentadienyl anion or cyclopentadienyl cation is not aromatic?

Explanation

To determine which of the two species, the cyclopentadienyl anion or cyclopentadienyl cation, is not aromatic, we will follow these steps:

### Step 1: Understand Aromaticity Criteria
A compound is considered aromatic if it meets the following criteria:
1. It is cyclic.
2. It is planar.
3. It has a complete conjugation of π (pi) electrons.
4. It follows Huckel's rule, which states that the number of π electrons must be of the form \(4n + 2\) (where \(n\) is a non-negative integer).
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