o-nitrophenol is

Options

A. more volatile than p-nitrophenol
B. less volatile than p-nitrophenol
C. Equally volatile as p-nitrophenol
D. Non-volatile

Answer

To determine the volatility of ortho-nitrophenol compared to para-nitrophenol, we need to analyze the molecular structures and the type of hydrogen bonding present in each compound.

### Step-by-Step Solution:

1. **Identify the Structures**:
- **Ortho-nitrophenol**: The structure consists of a hydroxyl group (-OH) and a nitro group (-NO2) attached to the benzene ring at adjacent positions (ortho position).
- **Para-nitrophenol**: The structure consists of a hydroxyl group (-OH) and a nitro group (-NO2) attached to the benzene ring at opposite positions (para position).

2. **Analyze Hydrogen Bonding**:
- **Ortho-nitrophenol**: In this compound, the -OH group can form an intramolecular hydrogen bond with the nitro group. This means that the hydrogen bonding occurs within the same molecule, which stabilizes the molecule but does not lead to strong intermolecular interactions.
- **Para-nitrophenol**: In this compound, the -OH group can form intermolecular hydrogen bonds with other para-nitrophenol molecules. This leads to stronger interactions between different molecules.

3. **Determine the Effect on Boiling Point**:
- **Boiling Point and Volatility Relationship**: The boiling point of a substance is inversely related to its volatility. A higher boiling point indicates lower volatility.
- **Ortho-nitrophenol** has intramolecular hydrogen bonding, which does not significantly increase its boiling point.
- **Para-nitrophenol** has intermolecular hydrogen bonding, which increases its boiling point due to stronger molecular association.

4. **Conclusion**:
- Since ortho-nitrophenol has a lower boiling point due to the lack of significant intermolecular hydrogen bonding, it is more volatile than para-nitrophenol.

### Final Answer:
Ortho-nitrophenol is **more volatile than para-nitrophenol**.

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