Which of these compounds are aromatic in character?

Options

A. Benzene
B. Pyrole
C. Pyridine
D. All of these

Answer

To determine which of the given compounds are aromatic in character, we need to evaluate each compound based on the criteria for aromaticity. A compound is considered aromatic if it meets the following three conditions:

1. **Planarity**: The compound must be planar.
2. **Conjugation**: The compound must have a continuous overlap of p-orbitals (conjugated system).
3. **Hückel's Rule**: The compound must have \(4n + 2\) π electrons, where \(n\) is a non-negative integer (0, 1, 2, ...).

Now, let's analyze each compound:

### Step 1: Analyze Benzene
- **Structure**: Benzene (C₆H₆) is a cyclic compound with alternating double bonds.
- **Planarity**: Benzene is planar.
- **Conjugation**: It has a continuous overlap of p-orbitals due to its alternating double bonds.
- **π Electrons**: Benzene has 6 π electrons (from the 3 double bonds).
- **Hückel's Rule**: \(n = 1\) gives \(4(1) + 2 = 6\). This satisfies Hückel's rule.

**Conclusion**: Benzene is aromatic.

### Step 2: Analyze Pyrrole
- **Structure**: Pyrrole (C₄H₄NH) has a five-membered ring with one nitrogen atom.
- **Planarity**: Pyrrole is planar.
- **Conjugation**: The nitrogen atom has a lone pair that can participate in the conjugated system.
- **π Electrons**: Pyrrole has 4 π electrons from the double bonds and 2 from the lone pair on nitrogen, totaling 6 π electrons.
- **Hückel's Rule**: \(n = 1\) gives \(4(1) + 2 = 6\). This satisfies Hückel's rule.

**Conclusion**: Pyrrole is aromatic.

### Step 3: Analyze Pyridine
- **Structure**: Pyridine (C₅H₅N) is a six-membered ring with one nitrogen atom.
- **Planarity**: Pyridine is planar.
- **Conjugation**: It has alternating double bonds, and the nitrogen does not contribute its lone pair to the π system.
- **π Electrons**: Pyridine has 6 π electrons from the 3 double bonds.
- **Hückel's Rule**: \(n = 1\) gives \(4(1) + 2 = 6\). This satisfies Hückel's rule.

**Conclusion**: Pyridine is aromatic.

### Final Conclusion
Since all three compounds (benzene, pyrrole, and pyridine) satisfy the criteria for aromaticity, we conclude that:

**All of these compounds are aromatic in character.**