Crystallization of Platonic-Solid Geometry Hydrocarbons Cubane (C8H8) and Dodecahedrane (C20H20) Affords Geometrical Changes
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Central European NMR Meeting 31st NMR Valtice
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The Platonic-Solid geometry hydrocarbons cubane (C8H8) and dodecahedrane (C20H20) exhibit all their respective 48 (Oh) and 120 (Ih) symmetry operations when dissolved in solution. This point group high symmetry engenders ideal carbon cube or dodecahedron skeletal geometries affording only one Nuclear Magnetic Resonance (NMR) Spectroscopy signal for their 13C or 1H nuclei. However, entering the constraints of a crystal lattice results in subtle, but measurable, changes to generate S6 and Th crystalline-state point group symmetries, respectively. The former cube now becomes an ideal 90 degree puckered hexagon with single carbons triply-bridging each of the top and bottom faces. The former dodecahedron now is changed into an ideal cube with two carbon long bridges to each of the cube?s six faces. Solid-state NMR spectra provide visually convincing evidence in the form of two separated 13C signals for on-axes: off-axes nuclei in the respective ratios of 2:6 (cubane) and 8:12 (dodecahedrane), M.C. Escher's periodic drawings provide a foundation in symmetry and crystallography.
1 Glaser, Robert Symmetry, Spectroscopy and Crystallography: The Structural Nexus, Wiley-VCH, Weinheim, 2015.
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