The molecular vibrations of coronene, both in-plane and out-of-plane, are studied. The simple Hückel molecular orbitals are derived and the CC bond oiders calculated. The bond orders are used to fix the CC stretching force constants. A complete set of independent symmetry coordinates is constructed. The in-plane vibrational frequencies are calculated by (a) the five-parameter approximation and (b) the Califano-Neto method; those of the out-of-plane vibrations only by the five-parameter approximation. The calculated frequencies are compared with observed values and previous calculations. A few new Raman bands are reported along with the presumably most complete set of infrared frequencies reported so far. A complete assignment of the infraredactive (Eiu and A2u) fundamentals is proposed. A majority of the Raman-active frequencies (Aig, Eig and E2g) are also assigned, using Raman, fluorescence and phosphorescence spectra.
The efficient synthesis of all-cis-[5.5.5.5]fenestrane (2) from the readily available intermediate 3 allowed the electron-diffraction analysis of 2. This structure analysis revealed long C-C bonds in the central C(C), fragment and a twist-envelope conformation for the four cyclopentane substructures. The four bridgehead H-atoms are in a synclinal rather than an ecliptic position with an approximate D, symmetry of 2. Planarizing distortions are evident from the opposite bond angles at the central C-atom being 116.2 0.5" with the remaining four being 103.7 i 0.2".
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