See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Determining the Most Acidic Phenol **Key Principle:** Acidity of phenols increases when electron-withdrawing groups (EWGs) are attached to the benzene ring, as they stabilize the negatively charged phenoxide ion ($PhO^-$). **Analysis of each compound:** **(A) 2,4-dinitrophenol:** Two $NO_2$ groups (para and ortho to $OH$) - EWG effect present but less optimal positioning **(B) 2,4,6-trinitrophenol:** Three $NO_2$ groups but all in meta/ortho positions relative to $OH$ - More $NO_2$ groups BUT meta position is weakly electron-withdrawing via inductive effect only **(C) 2,4,5-trinitrophenol:** Three $NO_2$ groups with **two at ortho and one at para position** - $NO_2$ at para (4-position): **Strongest electron-withdrawal** (resonance + inductive) - $NO_2$ at ortho positions (2,5): **Direct inductive withdrawal** - Maximum cumulative EWG effect → Maximum stabilization of $PhO^-$ **(D) 2,3,5-trinitrophenol:** Three $NO_2$ groups but none at para position - Lacks the most powerful para-directing electron withdrawal **Conclusion:** Option **(C)** has the optimal arrangement with $NO_2$ groups maximally positioned to withdraw electron density from the $OH$ group, making the hydrogen most acidic ($pK_a \approx 0.4$).