See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Analysis of Acid Strength **Step 1: Identify the acidic proton** All compounds contain $-NH_2$ groups. The acidic character depends on the **acidity of the N-H proton**, which increases when the $NH_2$ group is attached to an electron-withdrawing group. **Step 2: Evaluate electron-withdrawing effects** - **(A)** $-SO_2NH_2$ (sulfonamide): The $SO_2$ group is **highly electron-withdrawing** due to: - Two oxygen atoms directly bonded to sulfur - Strong inductive effect through $S=O$ bonds - Significantly withdraws electron density from $N$ - **(B)** $-CONH_2$ (primary amide): Carbonyl is electron-withdrawing but less than $SO_2$ - **(C)** Aniline ($-NH_2$ on benzene): The benzene ring is **electron-donating** (resonance effect), making $NH_2$ more basic, not acidic - **(D)** Cyclohexylamine ($-NH_2$ on saturated ring): Alkyl group is electron-donating, suppresses acidity **Step 3: Compare acidity** Electron withdrawal from $N$ weakens the $N-H$ bond and stabilizes the conjugate base ($-SO_2NH^-$), making the proton more acidic. $$\text{Acidity: (A) } >> \text{ (B) } > \text{ (D) } > \text{ (C)}$$ **Answer: (A)** — The sulfonamide group $-SO_2NH_2$ is the strongest acid due to maximum electron withdrawal by the $SO_2$ unit.