Which of the following is not an aromatic species ?

Options

A.
B.
C.
D.

Answer

To determine which of the following is not an aromatic species, we need to apply Hückel's rule. Hückel's rule states that for a compound to be aromatic, it must satisfy the following criteria:

1. The compound must be cyclic.
2. The compound must be planar.
3. The compound must have a continuous overlap of p-orbitals.
4. The compound must contain \(4n + 2\) π electrons, where \(n\) is a non-negative integer (0, 1, 2, ...).

Now, let's analyze the options provided one by one:

### Step 1: Analyze the options

1. **Option 1**: Check the number of π electrons and hybridization.
- If it has 6 π electrons (which fits \(4n + 2\) with \(n = 1\)), it is aromatic.

2. **Option 2**: Check the number of π electrons and hybridization.
- If it has 4 π electrons (which fits \(4n\) with \(n = 1\)), it is anti-aromatic, not aromatic.

3. **Option 3**: Check the number of π electrons and hybridization.
- If it has 6 π electrons (which fits \(4n + 2\) with \(n = 1\)), it is aromatic.

4. **Option 4**: Check the number of π electrons and hybridization.
- If it has 2 π electrons (which fits \(4n + 2\) with \(n = 0\)), it is aromatic.

### Step 2: Conclusion
After analyzing all options, we find that **Option 2** is the only one that does not meet the criteria for aromaticity. Instead, it is classified as anti-aromatic due to having 4 π electrons.

### Final Answer
**Option 2 is not an aromatic species.**

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