Which one of the following has aromatic character ?

Options

A. cyclopentadienyl catin
B. cyclopendienyl radical
C. cyclopendienyl anion
D. cyclopentadiene

Answer

To determine which of the given options has aromatic character, we need to apply Huckel's rule and check the conditions for aromaticity. Here’s a step-by-step solution:

### Step 1: Understand the Conditions for Aromaticity
A compound must satisfy the following conditions to be considered aromatic:
1. It must be cyclic.
2. It must be planar.
3. It must have a complete delocalization of π electrons.
4. It must contain \(4n + 2\) π electrons, where \(n\) is a non-negative integer (0, 1, 2, ...).

### Step 2: Analyze Each Option
Let’s analyze the options provided:

**Option 1: Cyclopentadienyl cation**
- Structure: It has 5 carbon atoms arranged in a cyclic manner.
- Hybridization: All carbons are sp² hybridized.
- π Electrons: The cation has 4 π electrons.
- Check Huckel's rule: \(4n + 2 = 4(0) + 2 = 2\) π electrons. Since it has 4 π electrons, it does not satisfy Huckel's rule.

**Conclusion for Option 1:** Not aromatic.

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**Option 2: Cyclopentadiene**
- Structure: It has 5 carbon atoms arranged in a cyclic manner.
- Hybridization: One carbon is sp³ hybridized (due to the double bond).
- π Electrons: It has 4 π electrons.
- Check Huckel's rule: It does not satisfy the planar condition due to the sp³ hybridization.

**Conclusion for Option 2:** Not aromatic.

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**Option 3: Cyclopentadienyl radical**
- Structure: It has 5 carbon atoms arranged in a cyclic manner.
- Hybridization: All carbons are sp² hybridized.
- π Electrons: The radical has 6 π electrons (4 from double bonds and 2 from the radical).
- Check Huckel's rule: \(4n + 2 = 4(1) + 2 = 6\) π electrons. It satisfies Huckel's rule.

**Conclusion for Option 3:** Aromatic.

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**Option 4: Cyclopentadiene anion**
- Structure: It has 5 carbon atoms arranged in a cyclic manner.
- Hybridization: One carbon is sp³ hybridized.
- π Electrons: It has 6 π electrons.
- Check Huckel's rule: It does not satisfy the planar condition due to the sp³ hybridization.

**Conclusion for Option 4:** Not aromatic.

### Final Answer
The compound with aromatic character is **Option 3: Cyclopentadienyl radical**.

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