MHTCET 25 Apr 2025 Shift 1 Paper

Concept:Lower $\mathrm{p}K_b$ value indicates higher basic strength of an amine.Explanation:Aliphatic amines are always more basic than aromatic amines because the lone pair on nitrogen is not delocalised into any ring.Ethylamine ($\mathrm{C_2H_5NH_2}$) is a primary aliphatic amine with a strong $+I$ effect, so the electron density on nitrogen is high.Trimethylamine ($\mathrm{(CH_3)_3N}$), though having three methyl groups, suffers from steric hindrance and poor solvation of its protonated form in water, making it less basic than ethylamine.Aniline ($\mathrm{C_6H_5NH_2}$) is the weakest base because the nitrogen lone pair is involved in resonance with the benzene ring.Benzylamine ($\mathrm{C_6H_5CH_2NH_2}$) is more basic than aniline but less basic than ethylamine, as the phenyl group withdraws electrons by the inductive effect.Therefore, ethylamine has the lowest $\mathrm{p}K_b$ among the given amines. Answer:Option A: $\mathrm{C_2H_5NH_2}$