Electronic origin of pyridinyl N as a better hydrogen-bonding acceptor than carbonyl O

A diarylamine compound, 2-(phenylamino)nicotinic acid, can form either the carboxyl acid-acid dimer or acid-pyridine chain in its polymorphic structures. Quantum mechanical calculations indicate that the hydrogen-bonding strength of the heterosynthon is stronger. Conceptual density functional theory is then used to understand the fundamental cause of pyridine N being a better hydrogen-bonding acceptor.