Conformation of acylureas. Solvent polarity dependent specific rotation and the formation of molecular complexes with solvent molecules possessing a carbonyl or epoxy functionality

In order to elucidate the conformation of acylurea which possesses intramolecular hydrogen bonding between the carbonyl and NH groups, the relation between solvent polarity [ET(30)] and specific rotation of 2,6-bis(ureidocarbonyl)naphthalene 1 was examined. A good linear relationship was observed, except for solvents with a carbonyl functionality. Some of these solvents formed molecular complexes with 1(molar ratio of 1: solvent, 1:2). Single crystal X-ray diffraction analysis of the molecular complex of 1 with ethyl acetate disclosed that the intramolecular hydrogen bonding was absent due to the intermolecular hydrogen bonding with ethyl acetate. In contrast, 2,4′-bis(ureidocarbonyl)benzophenone 2 formed 1:1 complexes with carbonyl compounds, and the bulkier -2,6-bis(ureidocarbonyl)naphthalene 3 could not form complexes with them.