On the correlation between ionization potentials and 13C- and 15N-chemical shifts in substituted pyridines

Abstract

A theory which predicts an approximately linear correlation between first ionization potentials and chemical shift is briefly presented. The theory is used to explain the correlation between the observed δ_c values for positions five and six and the ionization potentials for 2- and 3-substituted pyridines. Similarly, correlation of the nitrogen- 15 chemical shifts with the ionization potentials for 4-substituted pyridines is discussed. The solvent-induced changes in nitrogen- 15 chemical shifts can be correlated with the solvent-dependent HOMO energy for pyridine in solvents with different dielectric constants using a solvent cavity model. A correlation between the nitrogen- 15 chemical shift and solvent-dependent net atomic charge on nitrogen in pyridine is also observed. The relationship with the paramagnetic shielding of the nucleus is also discussed.