Solvent-oriented 1H NMR chemical shifts of pyridinium iodide and application of Buckingham equation

1H NMR studies of 1-ethyl-4-carbomethoxypyridinium iodide (Py+I−) have been carried out in various neat solvents with a dielectric constant range of 4.81–78.4. The effect of solvents on the chemical shifts of pyridinium ring protons (δ2,6 and δ3,5) have been studied to envisage and understand the interactions of positively charged pyridinium ring with the solvents. These interactions were found to decrease with the increase in solvent polarity. The solute parameters which are responsible for interactions with a polar solvent were calculated from the slopes and intercepts of Buckingham equation plots. A comparison in terms of solvent polarity parameters; the dielectric constant (ε) and the dielectric function (η) upon the above mentioned interaction was carried out which showed that the iodide ion (I−) is tilted more with increasing polarity of the solvent than being exactly perpendicular to the Py+ ring.The observed linear variation of δ2,6 and Δδ (the difference between the chemical shifts of ring protons, Δδ = δ2,6 − δ3,5) with various solvent polarity parameters, suggests that Δδ-values of Py+I− can be used as solvent polarity parameter in a similar fashion as Z-values. It may be more applicable in solvent selection during simultaneous organic synthesis and NMR analysis.