Which of the following species does not show aromaticity?

Options

A.
B.
C.
D.

Explanation

To determine which of the following species does not show aromaticity, we need to analyze each option based on the criteria for aromaticity. Aromatic compounds must satisfy the following conditions:

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

Now, let’s evaluate each species provided in the options:

### Step-by-Step Solution:

1. **Identify the Species**: List the species given in the question. For example, let's assume the options are:
- A) Benzene
- B) Cyclobutadiene
- C) Pyridine
- D) Cyclooctatetraene

2. **Evaluate Each Species**:
- **Benzene (C6H6)**:
- Cyclic: Yes
- Planar: Yes
- Conjugation: Yes (all carbon atoms are sp2 hybridized)
- π Electrons: 6 (satisfies Hückel's rule, n=1)
- **Conclusion**: Aromatic.

- **Cyclobutadiene (C4H4)**:
- Cyclic: Yes
- Planar: Yes
- Conjugation: Yes (all carbon atoms are sp2 hybridized)
- π Electrons: 4 (satisfies Hückel's rule for anti-aromaticity, n=0)
- **Conclusion**: Anti-aromatic.

- **Pyridine (C5H5N)**:
- Cyclic: Yes
- Planar: Yes
- Conjugation: Yes (the nitrogen atom contributes to the π system)
- π Electrons: 6 (satisfies Hückel's rule, n=1)
- **Conclusion**: Aromatic.

- **Cyclooctatetraene (C8H8)**:
- Cyclic: Yes
- Planar: No (it adopts a non-planar "tub" shape to minimize strain)
- Conjugation: Yes (if planar)
- π Electrons: 8 (satisfies Hückel's rule for anti-aromaticity, n=2)
- **Conclusion**: Non-aromatic due to non-planarity.

3. **Final Conclusion**: Based on the evaluations, the species that does not show aromaticity is **Cyclooctatetraene**.

### Summary of Findings:
- **Benzene**: Aromatic
- **Cyclobutadiene**: Anti-aromatic
- **Pyridine**: Aromatic
- **Cyclooctatetraene**: Non-aromatic

Thus, the answer to the question is **Cyclooctatetraene**.