Crystal structure of 1,2-dibenzoylacenaphthylene

Abstract

The title molecule, C26H16O2, crystallizes as a molecular crystal with no strong intermolecular interactions (the shortest C—H...O contact is longer than 3.4 Å). Two flat acenaphthylene groups of neigboring 1,2-dibenzoylacenaphthylene molecules are related by a crystallographic center of symmetry and are stacked with the distance between their mean planes of 3.37 (1) Å, apparently making an optimal close packing for these bulky aromatic moieties. Both carbonyl groups are oriented towards the same side of the planar acenaphthylene. The angles between the flat acenaphthylene group and the benzoyl groups are 62.6 (1) and 57.8 (1)°. Because rotation of the benzoyl groups is sterically hindered, we expect that the molecules will remain locked in this `pseudo-cis' orientation in solution. As a result, reduction of 1,2-dibenzoylacenaphthylene at low temperature with sodium dithionite yields thecis-isomer of 1,2-dibenzoyl-1,2-dihydroacenaphthylene, which is sterically favorable. This isomer is thermodynamically less favorable than thetransisomer, but it converts to the more stable isomer only on long-term heating (Greenberg & Schenendorf (1980).