The cyclopentadienyl cation is _________ while cyclopentadienyl anion is ________

Answer

To answer the question, "The cyclopentadienyl cation is _________ while cyclopentadienyl anion is ________," we will analyze the characteristics of both the cyclopentadienyl cation and anion based on their structures and electron counts.

### Step-by-Step Solution:

1. **Identify the Structures**:
- The cyclopentadienyl cation (C5H5^+) is derived from cyclopentadiene by removing one hydrogen atom, resulting in a positive charge.
- The cyclopentadienyl anion (C5H5^-) is formed by adding an extra electron to cyclopentadiene, resulting in a negative charge.

2. **Determine the Electron Count**:
- The cyclopentadienyl cation has 4 π electrons. This is because, in its structure, there are 2 double bonds contributing 2 π electrons each, and one of the π electrons is removed due to the positive charge.
- The cyclopentadienyl anion has 6 π electrons. This is because it retains the original 4 π electrons from the double bonds and gains an additional electron due to the negative charge.

3. **Apply Hückel's Rule**:
- According to Hückel's rule, for a compound to be aromatic, it must have (4n + 2) π electrons, where n is a non-negative integer.
- For the cyclopentadienyl cation (4 π electrons), it does not satisfy Hückel's rule (since 4 does not equal 4n + 2 for any integer n), thus it is classified as **anti-aromatic**.
- For the cyclopentadienyl anion (6 π electrons), it satisfies Hückel's rule (since 6 = 4(1) + 2), thus it is classified as **aromatic**.

4. **Conclusion**:
- Therefore, we can conclude that the cyclopentadienyl cation is **anti-aromatic** while the cyclopentadienyl anion is **aromatic**.

### Final Answer:
The cyclopentadienyl cation is **anti-aromatic** while cyclopentadienyl anion is **aromatic**.