Indirect 13C–1H coupling in asymmetrically trisubstituted benzenes: a carbon-13 nuclear magnetic resonance study

Abstract

Undecoupled ¹³C n.m.r. spectra of a series of asymmetrically trisubstituted benzenes have been obtained by proton ‘gated’-decoupling, and show invariably a characteristic sharp doublet in the aromatic region. The origin of this phenomenon is discussed in terms of the indirect ¹³C–¹H coupling pathways available within the ring as dictated by the positions of the substituents. It is shown that a doublet without fine structure arises from the carbon atom having no protons meta, that it is a generally predictable facet of these systems and as such a valuable aid to assignment.