Determination of the absolute stereostructure of a cyclic azobenzene from the crystal structure of the precursor containing a heavy element

Abstract

SummarySingle crystal X-ray diffraction has been used as one of the common methods for the unambiguous determination of the absolute stereostructure of chiral molecules. However, this method is limited to molecules containing heavy atoms or to molecules with the possibility of functionalization with heavy elements or chiral internal references. Herein, we report the determination of the absolute stereostructure of the enantiomers of molecule (E)-2, which lacks the possibility of functionalization, using a reverse method, i.e., defunctionalization of its precursor of known stereostructure with bromine substitution (S-(−)-(E)-1). A reductive debromination of S-(−)-(E)-1 results in formation of one of the enantiomers of (E)-2. Using a combination of HPLC and CD spectroscopy we could safely assign the stereostructure of one of the enantiomers of (E)-2, the reduced product R-(−)-(E)-1.

Molecular Crankshaft Effect Converting Piston-like Molecular Motion to Continuous Rotation of Macro Objects

“…Figure shows a series of two cycles of rotation and standstill state of a glass flake on the surface of CLC film under subsequent UV and visible light irradiation. According to the chiral nature of the embedded molecule 1 , the texture and glass flakes were rotated in either a clockwise (doped with S -(−)- E - 1 ) or a counterclockwise (doped with R -(−)- E - 1 ) fashion. Under UV irradiation, a glass flake on the surface of the CLC film ( S -(−)- E - 1 doped in ZLI-1132) has executed rotation in the clockwise direction as the result of rotational reorganization of the fingerprint texture, and rotation continued until reaching the photostationary state (PSS 366nm , Figure b,c,g,h).…”