Which among the following is not an aromatic species?

Options

A.
B.
C.
D.

Answer

To determine which among the given options is not an aromatic species, we can follow these steps:

### Step 1: 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 follow Huckel's rule, which states that it should have \(4N + 2\) π electrons, where \(N\) is a non-negative integer.

### Step 2: Analyze Each Option
Let's analyze each of the given options based on the criteria for aromaticity.

#### Option 1: Benzene
- Benzene is a cyclic compound with 6 π electrons (which fits \(N=1\) in Huckel's rule).
- It is planar and consists entirely of sp² hybridized carbons.
- **Conclusion**: Benzene is aromatic.

#### Option 2: Furan
- Furan is a five-membered ring containing one oxygen atom.
- It has 2 π electrons from the double bonds and 2 π electrons from the lone pair on oxygen, totaling 6 π electrons (fits \(N=1\)).
- It is planar due to sp² hybridization of the carbons.
- **Conclusion**: Furan is aromatic.

#### Option 3: Thiophene
- Thiophene is similar to furan but contains sulfur instead of oxygen.
- It also has 2 π electrons from the double bonds and 2 π electrons from the lone pair on sulfur, totaling 6 π electrons (fits \(N=1\)).
- It is planar due to sp² hybridization of the carbons.
- **Conclusion**: Thiophene is aromatic.

#### Option 4: A compound with an sp³ carbon
- This compound contains a carbon that is sp³ hybridized, which means it is tetrahedral and non-planar.
- The presence of an sp³ carbon breaks the cyclic and planar nature required for aromaticity.
- **Conclusion**: This compound is not aromatic.

### Final Answer
The option that is not an aromatic species is **Option 4**.

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