NOVEL O-C-C-O AND C-O-C-C STEREOCHEMISTRY IN CROWN-ETHER ANALOGS - X-RAY CRYSTAL-STRUCTURE AND NMR-STUDIES OF DIBENZO-20-CROWN-6

The X-ray crystal structure of the title material indicates that the molecule possesses a pseudo-centre of inversion. A pair of O-C-C-O bonds have a trans conformation in contrast to normal gauche stereochemistry for such units in crown ethers. For the C-O-C-C networks, which are normally transoid in crown ethers, all four such units involving methylene carbons of the 20-membered ring exhibit unusual geometries. Two units possess gauche conformations and the other two have torsion angles near 120 degrees. Solution H-1 and C-13 NMR spectra have been recorded as a function of temperature and C-13 solid state spectra are included.