Which of the following compound is Aromatic ?

Options

A.
B.
C.
D.

Answer

To determine which of the given compounds is aromatic, we need to follow a systematic approach based on the criteria for aromaticity. Here’s a step-by-step solution:

### Step 1: Understand the Criteria for Aromaticity
A compound is considered aromatic if it meets the following criteria:
1. It must be cyclic (form a ring).
2. It must be planar (all atoms in the ring must lie in the same plane).
3. It must have a continuous overlap of p-orbitals (conjugation).
4. It must contain \(4n + 2\) π electrons (Hückel's rule), where \(n\) is a non-negative integer.

### Step 2: Analyze Each Compound
Let's analyze each compound based on the criteria mentioned above.

#### Compound 1:
- Structure: Cyclobutane ring with a double bond and a positive charge.
- Analysis:
- The presence of an sp³ carbon indicates that it is not planar.
- There is no continuous conjugation due to the sp³ carbon.
- Conclusion: **Non-aromatic**.

#### Compound 2:
- Structure: Cyclobutane ring with two double bonds.
- Analysis:
- The molecule is planar and has conjugation.
- It has 4 π electrons (2 from each double bond).
- Conclusion: **Anti-aromatic** (since it follows \(4n\) rule, where \(n=1\)).

#### Compound 3:
- Structure: A six-membered ring with nitrogen and oxygen.
- Analysis:
- Contains sp³ carbons which disrupt conjugation.
- Cannot achieve resonance due to the presence of sp³ carbons.
- Conclusion: **Non-aromatic**.

#### Compound 4:
- Structure: A cyclic compound with double bonds and positive charges.
- Analysis:
- The compound is planar, allowing for resonance.
- It has 2 π electrons (from the double bonds).
- Conclusion: **Aromatic** (since it follows \(4n + 2\) rule, where \(n=0\)).

### Step 3: Final Answer
Based on the analysis, the only aromatic compound among the options provided is **Compound 4**.

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