Which of the following is non `-` aromatic in nature ?

Explanation

To determine which of the given structures is non-aromatic, we need to analyze the aromaticity of each compound based on the criteria of aromaticity. Aromatic compounds must be cyclic, planar, fully conjugated (p-orbitals overlapping), and follow Hückel's rule (4n + 2 π electrons, where n is a non-negative integer). Non-aromatic compounds do not meet these criteria.

### Step-by-Step Solution:

1. **Identify the Structures**: List the structures provided in the question. For this example, let's assume we have four structures: Azulene, a substituted benzene, pyrrole, and another cyclic compound.

2. **Analyze Azulene**:
- Azulene is a bicyclic compound with a total of 10 π electrons.
- It has delocalized electrons and is planar.
- Therefore, Azulene is aromatic.

3. **Analyze the Substituted Benzene**:
- A substituted benzene is typically planar and has 6 π electrons.
- It satisfies Hückel's rule (4n + 2) and is aromatic.

4. **Analyze Pyrrole**:
- Pyrrole is a five-membered ring with a lone pair on nitrogen contributing to the π system.
- It has 6 π electrons (4 from the double bonds and 2 from the nitrogen's lone pair).
- Pyrrole is planar and satisfies Hückel's rule, making it aromatic.

5. **Analyze the Fourth Structure (Assuming it is Non-Planar)**:
- If the fourth structure is not planar (for example, a non-planar cyclic compound), it cannot be aromatic.
- If it does not have a fully conjugated π system or does not meet the electron count criteria, it is non-aromatic.

6. **Conclusion**:
- Based on the analysis, the fourth structure is non-aromatic because it is not planar and does not have a fully conjugated π system.

### Final Answer:
The non-aromatic compound among the options is the fourth structure (assumed to be non-planar).

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