The presence of this conformer can also explain the high intensity observed around 1050 cm -1 . The predicted spectrum of the second candidate structure (labelled MDZ-N-glucuronide 2, yellow trace), provides an overall poorer match with the experiment. A feature of particular interest is the computed band near 1550 cm -1 , which corresponds to the C=N stretching vibration involving the glucuronated N-atom and is diagnostic for glucuronidation at this position. Moreover, the absence of a significant band around 1300 cm -1 in the MDZ-N-glucuronide 2 spectrum, where the MDZ-N glucuronide-1 computation predicts delocalized C-H bending vibrations, and the vibrational bands in the 600-900 cm -1 region, corresponding to delocalized vibrations, are diagnostic. These bands are likely affected by the largely different three-dimensional conformation induced by the different position of the glucuronide group. Overall, based on the better spectral match, we assign the MDZ-N-glucuronide 1 structure to compound D. Note that MDZ contains a third N-atom where