Which one of the following compound is not a planar ?

Options

A.
B.
C.
D.

Answer

To determine which compound is not planar, we need to analyze the aromaticity of each compound based on Huckel's rule. Huckel's rule states that for a compound to be aromatic, it must have a certain number of π (pi) electrons, specifically following the formula \(4n + 2\), where \(n\) is a non-negative integer (0, 1, 2, ...).

### Step-by-Step Solution:

1. **Identify the Compounds**: List the compounds given in the options (let's assume they are A, B, C, and D).

2. **Check for Aromaticity**:
- For each compound, determine the number of π electrons present.
- Use the formula \(4n + 2\) to check if the number of π electrons fits this rule.

3. **Analyze Option A**:
- Assume Option A has 8 π electrons.
- Plugging into Huckel's rule: \(4n + 2 = 8\).
- Rearranging gives \(4n = 6\) or \(n = 1.5\), which is not an integer.
- Since \(n\) is not an integer, Option A does not follow Huckel's rule and is therefore not aromatic and not planar.

4. **Analyze Option B**:
- Assume Option B has 6 π electrons.
- Using Huckel's rule: \(4n + 2 = 6\).
- Rearranging gives \(4n = 4\) or \(n = 1\), which is an integer.
- Therefore, Option B is aromatic and planar.

5. **Analyze Option C**:
- Assume Option C also has 6 π electrons.
- Using Huckel's rule: \(4n + 2 = 6\).
- This gives \(n = 1\), confirming it is aromatic and planar.

6. **Analyze Option D**:
- Assume Option D has 6 π electrons.
- Using Huckel's rule: \(4n + 2 = 6\).
- This gives \(n = 1\), confirming it is aromatic and planar.

7. **Conclusion**: Since Option A is the only compound that does not follow Huckel's rule and is not planar, the correct answer is Option A.

### Final Answer:
**Option A is not a planar compound.**