Chemistry - GOC Question with Solution | TestHub

(2) is an ordinary aliphatic amine : its lone pair is fully available (conjugate acid $\mathrm{p}{K}_{\mathrm{a}}$ ≈ 9-10), so it is the most basic. (3), the pyridine ring nitrogen, keeps its lone pair in an sp2 orbital outside the aromatic sextet and is available for protonation (conjugate acid $\mathrm{p}{K}_{\mathrm{a}}$ ≈ 5-6). (1), the amino group on the ring, has its lone pair delocalised into the aromatic ring (aniline-type), making it the least available. Hence 2 $>$ 3 $>$ 1.