See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

**Analyzing Water Solubility of Nitrophenols:** The solubility of phenolic compounds in water depends on hydrogen bonding capacity between the $-OH$ group and water molecules. **Step 1:** All three isomers ($o$-, $m$-, $p$-nitrophenol) have both $-OH$ and $-NO_2$ groups that can form hydrogen bonds with water. **Step 2:** The key difference is **intramolecular hydrogen bonding** in $o$- and $m$-nitrophenols: - **o-nitrophenol:** The $-NO_2$ group (ortho position) forms a strong intramolecular H-bond with the phenolic $-OH$, reducing its availability for intermolecular H-bonding with water - **m-nitrophenol:** Similarly experiences some intramolecular H-bonding (though weaker geometrically) **Step 3:** In **p-nitrophenol**, the $-NO_2$ group is far from the $-OH$ group, so **no intramolecular H-bonding occurs**. The phenolic $-OH$ remains "free" and readily forms intermolecular H-bonds with water molecules. **Step 4:** However, p-nitrophenol has higher symmetry and stronger crystal lattice energy, making it harder to dissolve despite having a "free" $-OH$ group. The electrostatic attractions in the solid state dominate. **Conclusion:** $p$-nitrophenol is **least soluble in water** due to its high lattice enthalpy and symmetric molecular packing in the solid state. **Answer: (D) p-nitrophenol**