High-pressure Raman studies of triquinacene and dodecahedrane

The dimerization of triquinacene (C10H10) to dodecahedrane (C20H20) has been a goal of organic chemists for more than three decades. An attempted synthesis of dodecahedrane from triquinacene using high pressure and near-UV radiation was not successful, but both hydrocarbons survived the 15 GPa treatment. There is no evidence for a pressure-induced transition in either of the materials. The results of high-pressure Raman spectroscopic investigations to 20 GPa on triquinacene and dodecahedrane are reported. Liquid triquinacene crystallizes near 0.2 GPa at 295 K and the Raman peaks associated with the molecular modes sharpen strikingly. In the crystal the external mode peaks exhibit a large pressure dependence, as expected, but the surprising fact is that the C-H stretching modes behave likewise. In dodecahedrane a similar effect is observed for the C-H stretching modes, but no external mode peaks are observed. The Raman data on dodecahedrane are compared with earlier results and calculations, which support the Ih symmetry for the molecule and an fcc lattice for the crystal.