Which of the following is not aromatic

Options

A. Benzene
B. Napthalene
C. Pyridine
D. 1,3,5 heptatriene

Explanation

To determine which of the given compounds is not aromatic, we need to understand the criteria for aromaticity. A compound is considered aromatic if it meets the following criteria:

1. It must be cyclic.
2. It must be planar.
3. It must have a continuous overlap of p-orbitals (conjugation).
4. It must follow Huckel's rule, which states that it should have (4n + 2) π electrons, where n is a non-negative integer.

Now, let’s analyze each of the options provided in the question:

1. **Benzene**:
- Structure: Cyclic, planar, and has 6 π electrons (which fits Huckel's rule with n=1).
- Conclusion: Benzene is aromatic.

2. **Naphthalene**:
- Structure: Cyclic, planar, and has 10 π electrons (which fits Huckel's rule with n=2).
- Conclusion: Naphthalene is aromatic.

3. **Pyridine**:
- Structure: Cyclic, planar, and has 6 π electrons (which fits Huckel's rule with n=1).
- Conclusion: Pyridine is aromatic.

4. **1,3,5-Heptatriene**:
- Structure: This compound is not cyclic; it is a linear hydrocarbon with alternating double bonds.
- Conclusion: Since it does not meet the criteria of being cyclic, it is not aromatic.

Based on the analysis, the compound that is not aromatic is **1,3,5-Heptatriene**.

### Final Answer:
The compound that is not aromatic is **1,3,5-Heptatriene**.