Which of the following is not a heterocyclic aromatic compound?

Options

A. (1) Pyridine
B. (2) Pyrrolidine
C. (3) Pyrrole
D. (4) Furan

Explanation

To determine which of the given compounds is not a heterocyclic aromatic compound, we will analyze each option step by step.

### Step 1: Understand the Definitions
- **Heterocyclic Compound**: A compound that contains a ring structure with at least one atom in the ring that is not carbon (e.g., nitrogen, oxygen).
- **Aromatic Compound**: A compound that follows Huckel's rule (4n + 2 π electrons) and has a cyclic structure with resonance.

### Step 2: Analyze Each Compound

1. **Pyridine**
- Structure: A six-membered ring with five carbon atoms and one nitrogen atom.
- Analysis: It is cyclic, contains nitrogen (heteroatom), and has resonance (aromatic).
- Conclusion: Pyridine is a heterocyclic aromatic compound.

2. **Cyclohexane**
- Structure: A six-membered ring composed entirely of carbon atoms.
- Analysis: It is cyclic but does not contain any heteroatoms (only carbon). It is not aromatic because it does not have resonance.
- Conclusion: Cyclohexane is not a heterocyclic aromatic compound; it is an alicyclic compound.

3. **Pyrrole**
- Structure: A five-membered ring with four carbon atoms and one nitrogen atom.
- Analysis: It is cyclic, contains nitrogen (heteroatom), and has resonance (aromatic).
- Conclusion: Pyrrole is a heterocyclic aromatic compound.

4. **Furan**
- Structure: A five-membered ring with four carbon atoms and one oxygen atom.
- Analysis: It is cyclic, contains oxygen (heteroatom), and has resonance (aromatic).
- Conclusion: Furan is a heterocyclic aromatic compound.

### Step 3: Identify the Answer
From the analysis:
- Pyridine: Heterocyclic aromatic
- Cyclohexane: Not heterocyclic aromatic (alicyclic)
- Pyrrole: Heterocyclic aromatic
- Furan: Heterocyclic aromatic

Thus, the compound that is **not a heterocyclic aromatic compound** is **Cyclohexane**.

### Final Answer
**Cyclohexane** is not a heterocyclic aromatic compound.

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