Among the following, the aromatic compound is

Options

A.
B.
C.
D.

Explanation

To determine which of the given compounds is aromatic, we will apply Huckel's rule, which states that a compound must satisfy three criteria to be classified as aromatic:

1. The structure must be planar.
2. There must be delocalization of π electrons.
3. The compound must have \(4n + 2\) π electrons, where \(n\) is a non-negative integer.

Now, let's analyze each compound step by step.

### Step 1: Analyze the First Compound (Cyclopropene)
- **Structure**: Cyclopropene is a three-membered ring with a double bond.
- **Planarity**: The structure is planar.
- **Delocalization**: There is delocalization of π electrons due to the double bond.
- **Count π Electrons**: Cyclopropene has 2 π electrons (from the double bond).
- **Check Huckel's Rule**: For \(n = 0\), \(4n + 2 = 2\). This condition is satisfied.

**Conclusion**: Cyclopropene is aromatic.

### Step 2: Analyze the Second Compound (Cyclopentene)
- **Structure**: Cyclopentene is a five-membered ring with one double bond.
- **Planarity**: The structure is planar.
- **Delocalization**: There is delocalization of π electrons.
- **Count π Electrons**: Cyclopentene has 4 π electrons (2 from the double bond and 2 from the carbocation).
- **Check Huckel's Rule**: For \(n = 1\), \(4n + 2 = 6\). For \(n = 0\), \(4n + 2 = 2\). This condition is not satisfied as it has 4 π electrons.

**Conclusion**: Cyclopentene is anti-aromatic.

### Step 3: Analyze the Third Compound (Cyclobutene)
- **Structure**: Cyclobutene is a four-membered ring with one double bond.
- **Planarity**: The structure is planar.
- **Delocalization**: There is delocalization of π electrons.
- **Count π Electrons**: Cyclobutene has 4 π electrons (2 from the double bond).
- **Check Huckel's Rule**: For \(n = 1\), \(4n + 2 = 6\). For \(n = 0\), \(4n + 2 = 2\). This condition is not satisfied as it has 4 π electrons.

**Conclusion**: Cyclobutene is anti-aromatic.

### Step 4: Analyze the Fourth Compound (Cyclopropene with a Lone Pair)
- **Structure**: This compound has a lone pair and is a three-membered ring.
- **Planarity**: The structure is planar.
- **Delocalization**: There is delocalization of π electrons.
- **Count π Electrons**: This compound has 4 π electrons (2 from the double bonds and 2 from the lone pair).
- **Check Huckel's Rule**: For \(n = 1\), \(4n + 2 = 6\). For \(n = 0\), \(4n + 2 = 2\). This condition is not satisfied as it has 4 π electrons.

**Conclusion**: This compound is also anti-aromatic.

### Final Conclusion
Among the given compounds, the only aromatic compound is **Cyclopropene**.

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