Proton Magnetic Resonance Spectra of 3-Pyridines: The Unsymmetrical Four-Spin ABXY and ABKL Systems

The high-resolution proton magnetic resonance spectra of four pyridine derivatives of the type[Complex chemical formula](R=Cl, Br, aldehyde and acetyl groups) are studied as ABXY and ABKL systems. Detailed analysis of these methods is made and it is shown that in the 3-pyridines the ABKL treatment gives as good an account of the observed spectra as the ABCD, both methods giving the same values for the molecular parameters vi and Jij. The analysis of the spectrum of the pyridine-3-carboxaldehyde shows an unexpected coupling of 0.44±0.05 cps between the aldehydic and the beta protons but no interaction with the alpha or gamma protons.