Proton Chemical Shifts of the γ-Substituted Pyridines

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Abstract
The protonchemical shifts have been obtained from the NMR spectra of nine γ‐substituted pyridines. The substituent‐induced chemical shifts, which were calculated by subtracting from each observed value the corresponding proton shift of the unsubstituted pyridine, were found to be comparable to the shielding parameters of the analogous substituted benzenes. Moreover, these chemical shifts can be fitted to the additivity relationship of Martin and Dailey which was obtained from the proton shieldings in substituted benzenes. Therefore the shielding mechanisms in the pyridines are probably the same as those in the benzenes. The failure of the calculated chemical shifts of the α and β protons in the pyridines to agree with observed shifts, as was also the case with the corresponding substituted benzenes, is interpreted as further evidence that the shieldings at positions ortho and meta to the substituents are not determined by the pi‐electron density variations alone.