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 3Jαβ and 4Jαε, slightly decrease 4Jαγ and 5Jαδ and have little effect on 3Jβγ. 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.