Which one of the following is the heterocyclic aromatic compounds?

Options

A. Pyrene
B. Thiophene
C. Phenol
D. Aniline

Answer

To determine which of the given compounds is a heterocyclic aromatic compound, we need to follow a systematic approach. Here’s a step-by-step solution:

### Step 1: Understand the Definitions
- **Heterocyclic Compound**: A compound that contains a ring structure with at least one atom that is not carbon (heteroatom), such as nitrogen, oxygen, or sulfur.
- **Aromatic Compound**: A compound that follows Huckel's rule, which states that a planar cyclic molecule must have (4n + 2) π electrons to be considered aromatic.

### Step 2: Analyze the Given Options
We need to evaluate the options provided to identify which one is a heterocyclic aromatic compound. The options are:
1. Pyridine
2. Phenol
3. Aniline
4. Thiophene

### Step 3: Evaluate Each Option
1. **Pyridine**:
- Structure: A six-membered ring with one nitrogen atom.
- π Electrons: It has 6 π electrons (from 5 carbons and 1 nitrogen).
- Conclusion: It is aromatic and heterocyclic.

2. **Phenol**:
- Structure: A six-membered carbon ring with a hydroxyl (OH) group.
- π Electrons: It has 6 π electrons but contains only carbon and hydrogen.
- Conclusion: It is not heterocyclic.

3. **Aniline**:
- Structure: A six-membered carbon ring with an amino (NH2) group.
- π Electrons: It has 6 π electrons but contains only carbon and hydrogen.
- Conclusion: It is not heterocyclic.

4. **Thiophene**:
- Structure: A five-membered ring with four carbon atoms and one sulfur atom.
- π Electrons: It has 6 π electrons (4 from the carbon atoms and 2 from the sulfur atom).
- Conclusion: It is aromatic and heterocyclic.

### Step 4: Identify the Correct Answer
From the analysis, both pyridine and thiophene are heterocyclic aromatic compounds. However, if we are to choose one based on the context of the question, **Thiophene** is the most commonly recognized heterocyclic aromatic compound among the options provided.

### Final Answer:
**Thiophene** is the heterocyclic aromatic compound.

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