The proton resonance spectra of heterocycles. Part VIII. Substituent effects on coupling constants in bicyclic heteroaromatic compounds and the prediction of chemical shifts from coupling constants

Abstract

Substituents affect coupling constants in bicyclic heteroaromatic compounds: they increase ³J_αβ and ⁴J_αε, slightly decrease ⁴J_αγ and ⁵J_αδ and have little effect on ³J_βγ. The regularities disclosed allow prediction of J in substituted systems. ortho-Substituent effects on chemical shifts relate to the corresponding ³J values in the unsubstituted compound, reflecting the dependence of both on partial bond fixation.