Identify the Aromatic compound in the following

Options

A. Tetra hydro furan
B. Pyridine
C. Cyclopenta dienyl anion
D. both 2 & 3

Explanation

To identify the aromatic compound among the given options, we will follow these steps:

### Step 1: Understand the Criteria for Aromaticity
A compound is considered aromatic if it meets the following criteria:
1. It is cyclic.
2. It is planar.
3. It follows Huckel's rule, which states that the compound must have \(4n + 2\) π electrons, where \(n\) is a whole number (0, 1, 2,...).

### Step 2: Analyze Each Compound

#### Option A: Tetrahydrofuran
- **Structure**: Tetrahydrofuran is a saturated compound derived from furan by hydrogenation.
- **Hybridization**: All carbons are sp³ hybridized, meaning there are no π bonds.
- **π Electrons**: Since there are no π bonds, there are no π electrons to delocalize.
- **Conclusion**: Tetrahydrofuran is **not aromatic**.

#### Option B: Pyridine
- **Structure**: Pyridine is a six-membered ring with one nitrogen atom.
- **Hybridization**: The carbon atoms are sp² hybridized, and there are three π bonds.
- **π Electrons**: Each π bond contributes 2 π electrons, giving a total of \(3 \times 2 = 6\) π electrons.
- **Huckel's Rule**: For \(n = 1\), \(4n + 2 = 6\). Thus, pyridine follows Huckel's rule.
- **Conclusion**: Pyridine is **aromatic**.

#### Option C: Cyclopentadienyl Anion
- **Structure**: Cyclopentadienyl anion consists of a five-membered ring with two double bonds and a negative charge.
- **Hybridization**: The carbons are sp² hybridized, and the negative charge contributes to the π system.
- **π Electrons**: There are 4 π electrons from the two double bonds and 2 additional π electrons from the negative charge, totaling \(4 + 2 = 6\) π electrons.
- **Huckel's Rule**: For \(n = 1\), \(4n + 2 = 6\). Thus, cyclopentadienyl anion follows Huckel's rule.
- **Conclusion**: Cyclopentadienyl anion is **aromatic**.

### Step 3: Final Conclusion
- **Option D**: The correct answer is that both **pyridine (Option B)** and **cyclopentadienyl anion (Option C)** are aromatic compounds.

### Summary
The aromatic compounds among the given options are:
- Pyridine (Option B)
- Cyclopentadienyl anion (Option C)