Basicity of Amines Weaker base:Smaller pKa for ammonium ion Stronger base:Larger pKa for ammonium ion ABLE181 Basicity of Some Common Amines pKa of pKa of Name Structure ammonium ion Name Structure ammonium ion Ammonia NH3 9.26 Heterocyclic amine Primary alkylamine Pyridine 5.25 Methylamine CH3NH2 10.64 Ethylamine CHgCH2NH2 10.75 Secondary alkylamine Pyrimidine 1.3 Diethylamine (CH3CH2)2NH 10.98 Pyrrolidine 1127 H Pyrrole 0.4 Tertiary alkylamine Imidazole 6.95 Triethylamine (CH3CH2)3N 10.76 Arylamine Aniline 4.63 NH2Weaker base: Smaller pKa for ammonium ion Stronger base: Larger pKa for ammonium ion Basicity of Amines