JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Compounds Containing Nitrogen

The three nitrogen compounds are pyridine, pyrrole and piperidine. Piperidine has an $s{p}^3$ nitrogen with a freely available lone pair and is the most basic. Pyridine keeps its lone pair in an in-plane $s{p}^2$ orbital, available but held more tightly, so it is less basic. In pyrrole the lone pair is drawn into the aromatic sextet and is essentially unavailable for protonation, making it the least basic. The decreasing order of basicity is piperidine $>$ pyridine $>$ pyrrole.