See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Basic Strength Order Analysis **Key Principle:** Base strength depends on electron density at the nitrogen lone pair. Electron-donating groups increase basicity; electron-withdrawing groups decrease it. ## Analysis of Each Base: **Structure I:** $Ph-NH-CO-CH_3$ - Amide nitrogen; lone pair delocalized into $C=O$ (resonance) - **Very weak base** (weakest) **Structure II:** $Ph-CO-NH-CH_3$ - Amide nitrogen; lone pair delocalized into aromatic carbonyl - **Very weak base** (similar to I) **Structure III:** $Ph-CO-CH_2-NH_2$ - Primary amine, but $-CO-$ (electron-withdrawing) is attached to benzene - Inductive withdrawal decreases electron density at $NH_2$ - **Moderately weak base** **Structure IV:** $H_2N-Ph-CO-CH_3$ (ortho/para) - Amine nitrogen is directly on benzene with electron-donating effect - $-NH_2$ (electron-donor) increases electron density on benzene ring - The benzene ring then donates electron density back to the amine - **Strongest base** (electron enrichment) ## Reasoning: - Structure IV: $-NH_2$ is an **activating/electron-donating** group → highest basicity - Structure III: $-CO-$ is **electron-withdrawing** → moderate basicity - Structures II & I: Amide nitrogens with resonance stabilization → minimal basicity **Correct Order:** $IV > III > II > I$ **Answer: (d)**