Crystals of 2,7-diphenyl-4,5-benzotropone, C23H160, are monoclinic, space group P2 Z, with unit-cell dimensions a = 10.683 (6), b = 16.536 (4), c = 10.055 (5) A, fl = 111.88 (5) o and Z = 4. The structure was solved by the direct method. Block-diagonal-matrix, least-squares refinement gave the final R value of 0.067 for 3281 observed reflexions. The geometries of the two crystallographically independent molecules are essentially the same except for the carbonyl groups which have an apparently large thermal motion. The sevenmembered rings in the molecules are nearly planar in spite of the steric hindrance of the phenyl groups, while a marked elongation of the single bonds adjoining the carbonyl group is observed. By reviewing the structural features of the 4,5-benzotropone system, it is concluded that the planar form of the seven-membered ring is more stable than the boat form, but the e.nergy difference between them is so small that the intra-and intermolecular interactions could result in various conformational changes of the ring.
Crystals of the title compound, C13H120, are orthorhombic, space group Pbca, a=19-750 (3), b= 13"448 (3), c = 7"422 (2)/~ and Z= 8. The structure was solved by the direct method and refined by the full-matrix least-squares method. The final R value was 0.056 for 1222 observed reflexions. The sevenmembered ring of the molecule takes a shallow, twisted boat form with a bow angle of 10.8 ° and a stern angle of 4-8 °. Significant elongation of the single bonds neighbouring the carbonyl group is observed [C(1)-C(2) 1.477/~.], primarily due to the non-bonded repulsions between the carbonyl O and methyl C atoms.
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