Which of the following effects are possible in ortho nitrophenol

Options

A. `-l` effect
B. `-R` (mesoeric) effect
C. Intermolecular H - bonding
D. All of these

Answer

To solve the question regarding the effects possible in ortho-nitrophenol, we will analyze the structure and the electronic effects of the nitro group and the hydroxyl group on the benzene ring.

### Step-by-Step Solution:

1. **Identify the Structure of Ortho-Nitrophenol**:
- Ortho-nitrophenol consists of a phenolic hydroxyl group (-OH) and a nitro group (-NO2) located on adjacent carbon atoms of the benzene ring. The structure can be represented as follows:
```
HO
|
C6H4
|
NO2
```

2. **Intramolecular Hydrogen Bonding**:
- In ortho-nitrophenol, the hydroxyl group can form a hydrogen bond with the nitro group due to their proximity. This is known as intramolecular hydrogen bonding. The hydrogen atom of the hydroxyl group can interact with the oxygen atom of the nitro group, stabilizing the molecule.
- **Conclusion**: Intramolecular hydrogen bonding occurs in ortho-nitrophenol.

3. **Negative Inductive Effect (−I Effect)**:
- The nitro group (-NO2) is a strong electron-withdrawing group due to its electronegative nitrogen and oxygen atoms. This group pulls electron density away from the benzene ring through the inductive effect.
- **Conclusion**: The −I effect is exhibited by the nitro group in ortho-nitrophenol.

4. **Negative Resonance Effect (−R Effect)**:
- The nitro group can also participate in resonance. It can withdraw electron density from the aromatic ring through resonance, where the lone pairs on the oxygen can delocalize into the ring, leading to a decrease in electron density.
- **Conclusion**: The −R effect is also exhibited by the nitro group in ortho-nitrophenol.

5. **Final Conclusion**:
- Since ortho-nitrophenol exhibits intramolecular hydrogen bonding, a negative inductive effect (−I), and a negative resonance effect (−R), all these effects are possible in ortho-nitrophenol.
- Therefore, the correct answer is **Option 4**, indicating that all effects are present.