2-Pyridinecarboxylic Acid

Abstract

The crystal structure of the title compound, C6H5NO2, has been redetermined to confirm that the space group C2/c is correct for the averaged structure in time and space. A zigzag chain is formed by the hydrogen bonds, N—H⋯N and O—H⋯O, and these protons are disordered around the twofold axis or the center of symmetry. The solid state high resolution 15N-CP/MAS NMR spectrum clearly revealed the two separate signals of protonated and nonprotonated N atoms. It was concluded that the intermolecular N—H⋯N hydrogen bond is asymmetric and hydrogen atom is trapped at one of the two nitrogen atoms. However, there is a crystallographic twofold axis through the mid point of the N⋯N bond. These facts indicate that the neutral molecules and zwitter ions are arranged alternately at local domains in the NMR time scale.