Indirect13C–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.

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