Figures 3b/c compare the IR spectrum of compound D to theoretical spectra of two candidate structures, see Figure . The two imine N-atoms of MDZ were considered as potential sites of glucuronidation. The majority of the experimental spectrum is well reproduced by the predicted spectrum of the candidate in Figure , labelled MDZ-N-glucuronide 1 (red trace). Again, the C=N and C=C stretching vibrations near 1600 cm -1 are slightly redshifted in the experiment and some intensity differences are observed. The shoulder of the carbonyl stretching vibration near 1800 cm -1 suggests the co-existence of multiple conformations in the ion population. Indeed, at 10 kJ/mol above the global minimum conformer, the computations predict a conformer with a different orientation of the carbonyl group, leading to a slightly different C=O stretch frequency (see Figure in the SI).