Introduction:
O-nitrophenol and P-nitrophenol are structural isomers of nitrophenol. The difference between these isomers lies in the position of the nitro group (-NO2) on the phenol ring. Despite having similar chemical properties, there is a significant difference in their volatility. O-nitrophenol is steam volatile, meaning it can be easily vaporized by steam, while P-nitrophenol is not.

Key Points:
Here are the reasons why O-nitrophenol is steam volatile while P-nitrophenol is not:

1. Difference in Molecular Structure:
- O-nitrophenol has the nitro group (-NO2) attached to the ortho position of the phenol ring, meaning it is adjacent to the hydroxyl group (-OH).
- P-nitrophenol has the nitro group attached to the para position of the phenol ring, meaning it is opposite to the hydroxyl group.
- The difference in the position of the nitro group affects the intermolecular forces between the molecules.

2. Intermolecular Hydrogen Bonding:
- O-nitrophenol can form intermolecular hydrogen bonding due to the presence of the hydroxyl group adjacent to the nitro group.
- The hydrogen bonding interactions increase the attractive forces between O-nitrophenol molecules, making it more volatile.
- These hydrogen bonds can be broken by steam, allowing O-nitrophenol to vaporize easily.

3. Absence of Intermolecular Hydrogen Bonding in P-nitrophenol:
- In P-nitrophenol, the nitro group is positioned opposite to the hydroxyl group, making it unable to form intermolecular hydrogen bonds.
- The absence of hydrogen bonding weakens the attractive forces between P-nitrophenol molecules.
- Consequently, P-nitrophenol has higher boiling point and lower volatility.

4. Impact of Intermolecular Forces:
- The presence of intermolecular hydrogen bonding in O-nitrophenol allows it to interact more strongly with steam molecules during vaporization.
- The stronger intermolecular forces between O-nitrophenol and steam facilitate its vaporization, making it steam volatile.
- On the other hand, P-nitrophenol lacks these strong intermolecular interactions, resulting in lower volatility and limited ability to vaporize with steam.

Conclusion:
In summary, the difference in the position of the nitro group affects the intermolecular forces and hydrogen bonding capabilities of O-nitrophenol and P-nitrophenol. O-nitrophenol can form intermolecular hydrogen bonds, making it steam volatile. In contrast, P-nitrophenol lacks these hydrogen bonding interactions, leading to lower volatility.