Peri Interactions in Naphthalene Diketones: A Preference for (Z,Z) Conformations

The crystal structures of 1,8-dibenzoylnaphthalene (9), 1,4,5,8-tetrabenzoylnaphthalene (10), and 1,8-diacetylnaphthalene (11) have been determined by X-ray diffraction. Diketone 9 crystallizes in triclinic space group P ^—1 with a = 7.924(2), b = 14.068(3), c = 7.876(1) Å, = 99.47(2), = 90.58(1), = 91.43(2)°. Tetraketone 10 crystallizes in monoclinic space group P2₁/c a = 7.374(4), b = 11.960(5), c = 15.524(5) Å, = 93.15(5)°. Diketone 11 crystallizes in orthorhombic space group Pbca a = 6.986(3), b = 15.946(4), c = 8.257(1) Å. Each of these naphthalene ketones adopt a (Z,Z) conformation, with torsion angles O—C—C¹—C^8a/O—C—C⁸—C^8a of 49.8°/44.5° (9), 52.1°/46.6° (10), and 44.8°/42.4° (11). The structures 9–11 are overcrowded with the distances between two neighboring carbonyl carbon atoms being significantly shorter than the sum of the van der Waals radii of two carbon atoms (342 pm): 293.4 pm (9), 281.6 pm (10), and 293.0 pm (11).