SYNTHESIS, CHARACTERIZATION, AND CRYSTAL-STRUCTURES OF 2 STRAINED CYCLIC DIACETYLENES AND THEIR PRECURSORS

The synthesis, characterization, and crystal structures of two novel s trained cyclic diacetylenes are reported. A discussion is presented ab out the relative bond distances of the diacetylenes compared to a prev iously reported strained cyclic diacetylene to further determine the d egree of aromaticity of that compound. ,10:13,14-Tetrabenzo-3,7,11,15, 17-pentadehydro[18] annulene (5) is triclinic, P(-)1, with alpha = 9.4 89(5), b = 10.550(5), c = 12.155(6) Angstrom, alpha = 100.50(4), beta = 106.50(4), gamma = 100.85(4)degrees. abenzo-3,7,11,15,19,23,25-hepta dehydro[26]annulene (7) is triclinic, P(-)1, with a = 9.611(2), b = 10 .388(3), c = 15.963(3) Angstrom, alpha = 88.67(2), beta = 76.25(1), ga mma = 68.69(2). In addition, two precursors of 5, 3 and 4 which have a helical twist, are reported. 1,2-ethynediyl-bis(2,1-phenylene-2,1-eth ynediyl-2, 1-phenylene-2,1-ethynediyl]bis[trimethyl-silane] (3) is mon oclinic, P2(1)/c, with a = 13.682(4), b = 9.787(2), c = 13.448(4) Angs trom, beta = 112.37(2)degrees. hynyldiyl)bis[2-[(2-ethynylphenyl)ethyn yl]-benzene (4) is monoclinic, P2(1)/n, with a = 15.951(3), b = 3.999( 1), c = 18.168(4) Angstrom. beta = 99.05(3)degrees.