See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

# Solution: Arranging Amines by Increasing pKb **Key Principle:** Higher basicity = Lower pKb. Basicity of amines depends on: - Electron density on nitrogen - Alkyl group stabilization of conjugate acid --- **Analysis of each amine:** **(a) $HC \equiv C-CH_2-NH_2$ (Propargylamine)** - Alkyne is strongly electron-withdrawing (sp-hybridized carbon) - Reduces electron density on $NH_2$ - **Least basic → Highest pKb** ≈ 8.4 **(b) $CH_2=CH-CH_2-NH_2$ (Allylamine)** - Alkene is weakly electron-withdrawing - Intermediate electron density on $NH_2$ - **Moderately basic** → pKb ≈ 9.7 **(c) $CH_3-CH_2-CH_2-NH_2$ (Propylamine)** - Only alkyl groups (electron-donating) - Highest electron density on $NH_2$ - Alkyl groups stabilize the conjugate acid effectively - **Most basic → Lowest pKb** ≈ 10.6 --- **Order of basicity:** c > b > a **Order of pKb:** a > b > c → **c < b < a** **The answer is (A) c < b < a** ✓