The complete analysis of the 1H NMR spectra of quinoline and two of its derivatives. sign determinations of inter-ring coupling constants by means of the INDOR technique

The complete ¹H NMR spectral analyses of quinoline and two of its derivatives (4,7-dichloroquinoline and 8-nitroquinoline) have been performed. All the long-range coupling constants were determined both in magnitude and sign. In determining the signs the INDOR technique was very useful and successful, allowing the resolution of transitions as close as a few hundredths of a Hz. The signs of the inter-ring coupling constants alternate with the number of intervening bonds, according to McConnell's rule, except the all-trans⁶J couplings. A linear relationship has been found between the ¹H?¹H and ¹⁹F?¹⁹F inter-ring coupling constants for which the spin polarization is transmitted almost exclusively via the π-electron system.