Inter-ring Long-range Spin-Spin Proton Coupling in some 8-Hydroxyquinoline Derivatives

A study of the ¹H NMR spectra of a series of 8-hydroxyquinolines has been carried out using the 2D-COSYLR method and inter-ring proton spin-spin coupling constants ⁴J, ⁵J, ⁶J and ⁷J have been detected; it has been established that the π- mechanism for transmission of spin–spin coupling predominates and in the case of the planar zig-zag arrangement this results in unexpected annulment of ⁶J_2,7 and ⁶J_3,6.