Coupling constants in N-substituted pyridines and their relation with electronegativity

The coupling constants obtained from the complete spectral analysis of series of 1- and 3-substituted pyridine N-imides are related linearly to the electronegativities of the substituent atoms. The main conclusions of the papers by Cox, Castellano and Sun, and Castellano and Kostelnik are substantiated. The inductive effects of the first atoms of the substituents largely determine the coupling between protons in the ring system; delocalisation of π-electrons in the ring produces a much smaller effect.