Hydrogen Bonding of Bilirubins and Pyrromethenones in Solution

Abstract

Abstract Analysis of bilirubin and pyrromethenone N—H 1 H‐NMR chemical shifts indicates that in CDCl 3 solvent, where intermolecularly H‐bonded dimers or intramolecularly H‐bonded conformations are involved, the lactam N—H groups are more deshielded than the broader pyrrole N—H groups. In d 6 ‐DMSO, disaggregation and unfolding occurs with H‐bonding to the solvent and the sharper lactam N—H resonances becoming more shielded than the pyrrole N—H signals.