Which of the following compouds is not aromatic

Options

A.
B.
C.
D.

Answer

To determine which of the given compounds is not aromatic, we need to follow 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. **Cyclic Structure**: The compound must be cyclic.
2. **Planarity**: The compound must be planar, allowing for overlap of p-orbitals.
3. **Conjugation**: There must be a system of conjugated pi electrons.
4. **Hückel's Rule**: The compound must have \(4n + 2\) pi electrons, where \(n\) is a non-negative integer (0, 1, 2, ...).

### Step 2: Analyze Each Compound
We will analyze each compound based on the criteria mentioned above.

#### Compound 1:
- Structure: Contains a cyclic structure with sp² hybridized carbons.
- Pi Electrons: 6 pi electrons (2 from double bonds and 4 from lone pairs).
- Conclusion: Fulfills Hückel's rule (n=1), hence it is aromatic.

#### Compound 2:
- Structure: Similar to Compound 1, also cyclic and planar.
- Pi Electrons: 6 pi electrons (similar reasoning as Compound 1).
- Conclusion: Fulfills Hückel's rule (n=1), hence it is aromatic.

#### Compound 3:
- Structure: Contains a cyclic structure and resonance.
- Pi Electrons: 6 pi electrons (2 from double bonds and 4 from lone pairs).
- Conclusion: Fulfills Hückel's rule (n=1), hence it is aromatic.

#### Compound 4:
- Structure: Contains a cyclic structure but has 8 pi electrons.
- Pi Electrons: 8 pi electrons (2 from double bonds and 6 from lone pairs).
- Conclusion: Does not fulfill Hückel's rule (n=2), hence it is anti-aromatic and not aromatic.

### Step 3: Identify the Non-Aromatic Compound
From the analysis, we find that **Compound 4** is the one that does not meet the criteria for aromaticity.

### Final Answer:
**Option 4 is the compound that is not aromatic.**

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