• The subtle but significant difference in the exact location of the transitions and the resulting experimental lines and peaks vs. the first-order expression of the actual chemical shifts and coupling constants in the coupling tree, indicates the presence of a non-first order effect in the spin system. This is caused by the relative proximity of the resonances of the tightly J-coupled H-8 methylene hydrogens. The presence of higherorder coupling effects is also indicated by the difference between the center of the experimental splitting pattern (the minimum of the central "doublet") vs. the actual resonance frequency of H-9a, which is located at the center of the overall experimental intensity of this signal.