Determination of the Handedness of Urea Inclusion Compounds

Since the discovery of urea inclusion compounds (UICs) in 1940, the handedness of this chiral helical system has not been established experimentally. Here three UIC systems containing only light atoms were studied. The optical rotations were first measured, and the absolute structures of the enantiomorphic domains of three UICs were determined by single crystal X-ray diffraction (SCXRD). The correlation between the optical rotation and the absolute configuration of the UICs was finally established, showcasing the power of absolute structure determination by SCXRD, which is essential in structural chemistry and pharmaceutical research. To establish the correlation between the optical rotation and the absolute structure of urea inclusion compounds (UICs), three pairs of enantiomorphic UICs were studied. This successful experimental elucidation of the handedness of UICs not only settled a question that has lasted half a century, but also showcased the feasibility of absolute structure determination by single crystal X-ray diffraction (SCXRD).image