Figure 1.

NMR spectra fine structure and isotopomers. For a given ¹³C labeled carbon in the carbon chain of metabolite M (C2 in this example), the resonance fine structure depends on the labeling of the direct neighbors C1 and C3. (a) Unlabeled C1 and C3 correspond to the singlet M₂s. (b) Labeled C1 and unlabeled C3 correspond to the doublet M₂d₁₂, the frequency gap between the two peaks being the scalar coupling constant between C1 and C2, J_C1C2. (c) Unlabeled C1 and labeled C3 correspond to the doublet M₂d₂₃, the frequency gap being J_C2C3. (d) Simultaneously labeled C1 and C3 correspond to the doublet of doublet M₂q.