Crystal structure of 1,2-di-benzoyl-ace-naphthyl-ene.

The title mol-ecule, C26H16O2, crystallizes as a mol-ecular crystal with no strong inter-molecular inter-actions (the shortest C-H⋯O contact is longer than 3.4 Å). Two flat ace-naphthyl-ene groups of neigboring 1,2-di-benzoyl-ace-naphthyl-ene mol-ecules 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 ace-naphthyl-ene. The angles between the flat ace-naphthyl-ene 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 mol-ecules will remain locked in this 'pseudo-cis' orientation in solution. As a result, reduction of 1,2-di-benzoyl-ace-naphthyl-ene at low temperature with sodium di-thio-nite yields the cis-isomer of 1,2-dibenzoyl-1,2-di-hydro-ace-naphthyl-ene, which is sterically favorable. This isomer is thermodynamically less favorable than the trans isomer, but it converts to the more stable isomer only on long-term heating (Greenberg & Schenendorf (1980 ▸).