Proton magnetic resonance spectra of methylacridines. The relative signs of the inter‐ring coupling constants

High‐resolution proton spectra of acridine and the five monomethyl derivatives have been analyzed using multiple resonance and computer techniques. It was possible to determine the magnitudes and relative signs of the inter‐ring coupling constants between H‐C(9) and all the protons of the adjacent rings. Positive signs have been obtained for 5 J 29 and 5 J 49 , negative signs for 4 J 19 and 6 J 39 . The coupling constants are discussed in terms of σ‐ and π‐contributions and as a function of the geometry of the pathway.