Qualitative analysis of the geometry of the hydrogen bond in the homoconjugated pyridine ion

A theoretical analysis of the geometry of the isolated homoconjugated ion formed by interaction of the pyridine molecule with the pyridinium cation was performed. With no o-substituents and no external electric field applied, the hydrogen bond is strongly asymmetric and is characterized by a low barrier to proton transfer between the two chemically equivalent structures. According to the calculations, the most probable averaged distance between the nitrogen atoms forming the hydrogen bond in such homoconjugated cations is about 2.7 +/- 0.1 angstrom.