Amide–Amide Hydrogen Bonding. Semirubin Amides

Summary. Semirubins are analogs for one-half of the bilirubin structure and capable of intramolecular hydrogen bonding. Semirubin amides of ammonia and primary amines are also capable of intramolecular hydrogen bonding. From a combination of spectroscopic methods (¹H NMR, NOE, and VPO), the primary amide is found to engage very effectively in intramolecular hydrogen bonding. The secondary and tertiary amides engage in both intramolecular (i) and intermolecular (ii) hydrogen bonding: N-methyl (i, monomer + ii, dimer), N-tert-butyl (ii, dimer), N,N-diethyl (i, monomer + ii, dimer). With an oxo-group at C(10), all of the amides are monomeric and most engage in intramolecular hydrogen bonding.