Orthonitrophenol is steam volatile but paranitrophenol is not because .

Answer

To understand why ortho-nitrophenol is steam volatile while para-nitrophenol is not, we can analyze the structures and the types of hydrogen bonding present in each compound.

### Step 1: Draw the Structures
1. **Ortho-nitrophenol**: In this compound, the nitro group (-NO2) is attached to the benzene ring at the ortho position (adjacent to the hydroxyl group -OH).
- Structure:
```
OH
|
C6H4-NO2
```

2. **Para-nitrophenol**: In this compound, the nitro group is attached at the para position (opposite to the hydroxyl group).
- Structure:
```
OH
|
C6H4-NO2
```

### Step 2: Analyze Hydrogen Bonding
3. **Ortho-nitrophenol**: The proximity of the -OH group and the -NO2 group allows for intramolecular hydrogen bonding. This means that the hydrogen atom of the hydroxyl group can form a bond with the oxygen atom of the nitro group within the same molecule.
- This intramolecular hydrogen bonding stabilizes the molecule and lowers its boiling point, making it steam volatile.

4. **Para-nitrophenol**: In this case, the -OH and -NO2 groups are further apart, which leads to intermolecular hydrogen bonding. This means that the hydrogen bonding occurs between different molecules of para-nitrophenol.
- The presence of strong intermolecular hydrogen bonds increases the boiling point of para-nitrophenol, making it less volatile and not steam volatile.

### Step 3: Conclusion
5. **Final Statement**: Therefore, the reason ortho-nitrophenol is steam volatile while para-nitrophenol is not is due to the presence of intramolecular hydrogen bonding in ortho-nitrophenol, which lowers its boiling point, compared to the intermolecular hydrogen bonding in para-nitrophenol, which raises its boiling point.

### Summary
- **Ortho-nitrophenol**: Intramolecular hydrogen bonding → Lower boiling point → Steam volatile.
- **Para-nitrophenol**: Intermolecular hydrogen bonding → Higher boiling point → Not steam volatile.