MOLECULAR TOPOLOGY OF DI(9-ANTHRYL)ETHANEDIONE (9,9'-ANTHRIL) AND SOME GENERICALLY RELATED CYCLIC 1,2-DIKETONES

The molecular structures of di(9-anthryl)ethanedione (9,9'-anthril) and those of four 1,2-diketones derived from 9,9'-anthril by way of intramolecular cycloadditions were investigated by single-crystal X-ray diffraction studies. Two crystal modifications of 9,9'-anthril were available and found to differ in the dihedral angles (43.9 and 178.3-degrees) about the 1,2-dicarbonyl moiety. The 1,2-dicarbonyl group of the cyclobutanedione moiety in the anthril 4-pi+4-pi cyclomer is associated with a dihedral angle of 2.6-degrees. In the anthril isomer derived by 4-pi+2-pi cycloaddition, an exceptionally long single bond is indicative of molecular strain. The molecular structures of a keto enol and of a novel 1,2-diketo substituted triptycene, both obtained from the 4-pi+2-pi cyclomer by acid-catalysed rearrangement and dehydrogenation, respectively, were established. The topological and spectroscopic differences between the keto enol and its 1,2-diketo precursor are discussed.