2,3,4,5-TETRAPHENYLCYCLOPENTA-2,4-DIEN-1-ONE AND 5,6,7,8-TETRACHLORO-3A,9A-DIHYDRO-2,3,3A,9A-TETRAPHENYLCYCLOPENTA[2,3-B][1,4]BENZODIOXIN-1-ONE-TOLUENE (2/1) - COMPOUNDS OF PHOTOCHEMICAL INTEREST

(I) C29H20O, M(r) = 384.45, monoclinic, C2/c, a = 26.16 (2), b = 8.38 (1), c = 21.57 (2) angstrom, beta = 119.5 (2)degrees, V = 4115.6 angstrom 3, Z = 8, D(x) = 1.24 Mg m-3, lambda(Cu K-alpha) = 1.5418 angstrom, mu = 4.9 cm-1, F(000) = 1616, T = 293 K, R = 0.063 for 1789 reflexions. (IIIa) C35H20Cl4O3.0.5C7H8, M(r) = 676.42, monoclinic, P2(1)/a, a = 18.26 (2), b = 10.50 (1), c = 17.74 (2) angstrom, beta = 109.6 (1)degrees, V = 3204.2 angstrom 3, Z = 4, D(x) = 1.40 Mg m-3, lambda(Cu K-alpha) = 1.5418 angstrom, mu = 35.2 cm-1, F(000) = 1394, T = 293 K, R = 0.079 for 2461 reflexions. The mechanisms of photolytic ring closure in tetraphenylcyclopentadienone (I) and its adduct (IIIa) with tetrachloro-omicron-benzoquinone are still in doubt. In the crystal the non-bonded C...C distances of the atoms linked during photolysis are 3.264 (6) angstrom (I) and 3.208 (7) angstrom (IIIa). Packing-energy calculations suggest that the observed structures are stabilized by lattice forces and that the phenyl groups are further from coplanarity with the central ring in the free molecule.