Question

Explain why ortho-nitrophenol is more steam volatile than para-nitrophenol.

• A. Ortho-nitrophenol forms stronger intermolecular hydrogen bonds.
• B. Para-nitrophenol exhibits intramolecular hydrogen bonding.
• C. Ortho-nitrophenol forms intramolecular hydrogen bonds, reducing intermolecular attraction.
• D. Para-nitrophenol has a lower molecular weight than ortho-nitrophenol.

Hint:

Intramolecular hydrogen bonding leads to reduced intermolecular attraction and increased volatility. Intermolecular hydrogen bonding leads to increased intermolecular attraction and decreased volatility.

Answer 1

The Correct Option is C

Step 1: Understand steam volatility and its relation to intermolecular forces.
Steam volatility refers to the ability of a substance to vaporize with steam. A substance is more steam volatile if it has a lower boiling point and relatively weaker intermolecular forces, allowing it to easily escape into the gas phase along with water vapor. Step 2: Analyze hydrogen bonding in ortho-nitrophenol.
In ortho-nitrophenol, the hydroxyl (-OH) group and the nitro (-NO\(_2\)) group are adjacent to each other on the benzene ring.
This close proximity allows the hydrogen atom of the -OH group to form a hydrogen bond with an oxygen atom of the -NO\(_2\) group within the same molecule. This is known as intramolecular hydrogen bonding.
This internal hydrogen bonding effectively "ties up" the polar -OH group, making it less available to form hydrogen bonds with other ortho-nitrophenol molecules. Consequently, the overall intermolecular forces between ortho-nitrophenol molecules are weaker. Step 3: Analyze hydrogen bonding in para-nitrophenol.
In para-nitrophenol, the -OH and -NO\(_2\) groups are positioned opposite to each other. Their distance prevents the formation of intramolecular hydrogen bonds.
Instead, para-nitrophenol molecules form strong intermolecular hydrogen bonds with \textit{other} para-nitrophenol molecules. This leads to the association of molecules into larger aggregates.
These strong intermolecular forces require significantly more energy to overcome, resulting in a higher boiling point and lower volatility. Step 4: Conclude based on the comparison.
Because ortho-nitrophenol forms intramolecular hydrogen bonds, its molecules are less associated with each other through intermolecular forces. This makes them easier to separate and vaporize, leading to higher steam volatility compared to para-nitrophenol, which forms strong intermolecular hydrogen bonds causing greater molecular association.