Abstract
Publisher Summary This chapter focuses on spin–spin interactions between protons directly attached to the same aromatic or heterocyclic ring. There is a marked decrease in the ortho coupling constants on passing from six-membered to five-membered rings; however, the meta coupling constants, while exhibiting considerable scatter in values, do not show this trend. In general, substitution of a heteroatom for the —CH= group in hetero-aromatic systems appears to lead to a decrease in ortho coupling constants across the adjacent bond, in line with the effects of electronegative substituents. As the introduction of heteroatoms also alters both bond orders and bond angles, it is difficult to separate these effects. The ortho coupling constants in aromatic and heterocyclic molecules are closely related to cis-vicinal coupling constants in olefins. The meta coupling constants have been recognized as abnormally large for an interaction taking place across four bonds and not involving π-electrons.
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