Assignment of the NMR spectra of benzo[b]triphenyleno[1,2-d]thiophene through the application of zero quantum proton-proton correlation combined with proton-detected long-range multiple quantum heteronuclear chemical shift correlation

Assignment of the congested proton and carbon NMR spectra of heterocyclic benzo[b]triphenyleno[1,2‐d]thiophene was accomplished through the concerted application of several two‐dimensional NMR experiments. The inherent insensitivity of homonuclear zero quantum coherence to magnetic field inhomogeneity was used to advantage in disentangling the heavily overlapped proton NMR spectrum. Direct heteronuclear pairings were established using heteronuclear correlation with broad band homonuclear vicinal proton decoupling. Limited sample availability and solubility precluded complete establishment of long‐range heteronuclear correlations by conventional means. Proton‐detected long‐range heteronuclear multiple quantum coherence did, however, provide sufficient long‐range heteronuclear correlations to complete the assignment. A comparison of the data obtained from COSY and zero quantum experiments is presented; the ability of each to establish proton connectivities is discussed. Sensitivity limitations inherent in the conventional long‐range optimized heteronuclear chemical shift correlation experiment are contrasted with the advantages of the proton‐detected long‐range heteronuclear multiple quantum correlation experiment. Practical limitations of the latter are considered.