13C-NMR experimental methods for determination of resonance multiplicities: Strychnos alkaloids

13C-NMR spectral assignments of the Strychnos alkaloids brucine and strychnine have been reported by numerous investigators. One recent report contained several disparities in the assignments that were attributable to incorrect determinations of spin multiplicities. The source of the inaccuracies in the spin-multiplicity determinations of very complex molecules is discussed, and several additional techniques for the determination of these multiplicities are described that are less subject to interpretational errors than the conventional and routinely employed single-frequency off-resonance decoupling methods. These procedures are applied using brucine as a representative example.