Nuclear quadrupole resonance and molecular orbital studies of charge distribution in H‐bonded complexes of 2‐chloro‐4‐nitrobenzoic acid

The charge distribution in hydrogen bridges of varying strengths in solid 2‐chloro‐4‐nitrobenzoic acid complexes was studied using the 35 Cl nuclear quadrupole resonance technique (NQR). The dependence of 35 Cl NQR frequencies on the proton affinities was analysed. Molecular orbital calculations using atom superposition and electron delocalization molecular orbital theory showed that the trends of changes in the charge density on the chlorine, nitrogen and oxygen atoms, and on the binding energy and the bond order of NH and OH groups are consistent with the NQR results. Also, the agreement between theoretical and experimental results showed that the 3,5‐dimethylpyridine complex represents the critical point at 50% proton transfer.