Which of the following species is aromatic?

Options

A.
B.
C.
D.

Answer

To determine which of the given species is aromatic, we need to apply the criteria for aromaticity. Aromatic compounds must satisfy the following conditions:

1. **Cyclic structure**: The molecule must be cyclic.
2. **Planarity**: The molecule must be planar, allowing for overlap of p-orbitals.
3. **Complete conjugation**: There must be a continuous overlap of p-orbitals, allowing for delocalization of electrons.
4. **Hückel's rule**: The molecule must have (4n + 2) π electrons, where n is a non-negative integer.

Now, let's analyze each option step by step:

### Step 1: Analyze the first option
- **Hybridization**: The atom in the first option is sp³ hybridized.
- **Planarity**: Since sp³ hybridized atoms are tetrahedral, this structure is not planar.
- **Conclusion**: This species does not meet the criteria for aromaticity.

### Step 2: Analyze the second option
- **Hybridization**: The atoms in the second option are sp² hybridized.
- **Cyclic structure**: It is a closed ring.
- **Conjugation**: The structure allows for delocalization of π electrons.
- **Electron count**: It has 6 π electrons, which fits Hückel's rule (4n + 2, where n = 1).
- **Conclusion**: This species is aromatic.

### Step 3: Analyze the third option
- **Electron count**: This species has 4 + 4 π electrons.
- **Hückel's rule**: It does not satisfy Hückel's rule as it has 8 π electrons, which does not fit the (4n + 2) rule.
- **Conclusion**: This species is not aromatic.

### Step 4: Analyze the fourth option
- **Electron count**: This species has 8 π electrons.
- **Hückel's rule**: Similar to the third option, it does not satisfy Hückel's rule.
- **Conclusion**: This species is not aromatic.

### Final Conclusion
The only species that meets all the criteria for aromaticity is the second option. Therefore, the correct answer is:

**Option 2 is aromatic.**

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