Question

Which among the following has highest melting point ?

• A. Phenol
• B. o-Nitrophenol
• C. p-Nitrophenol
• D. p-Cresol

Hint:

Strong intermolecular hydrogen bonding and good packing raise the melting point.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Melting point depends on intermolecular forces and on how well molecules pack in the crystal.

Step 2: o-Nitrophenol:
In o-nitrophenol the \(\text{-OH}\) and \(\text{-NO}_2\) groups are close, so they form intramolecular hydrogen bonds. This leaves little hydrogen bonding between molecules, so its melting point is low (about 45 C).

Step 3: p-Nitrophenol:
In p-nitrophenol the groups are far apart, so only intermolecular hydrogen bonds form, linking many molecules together. It also packs well. Its melting point is about 114 C, the highest here.

Step 4: Others:
Phenol melts at about 41 C and p-cresol at about 35 C, both lower because they lack the strongly polar nitro group.

Final Answer:
p-Nitrophenol has the highest melting point, option (C). \[ \boxed{\text{p-Nitrophenol}} \]