The structure of tricyclo[3.3.2.02.8]decane (hexahydrobullvalene) – A gas-phase electron diffraction (GED) study

The molecular structure of tricyclo[3.3.2.02.8]decane (hexahydrobullvalene) has been determined experimentally by gas-phase electron diffraction as well as by quantum chemical calculations. The bond lengths (twofold standard deviations in parentheses) in the skeleton [1.496(7) in the cyclopropane ring, 1.527(10) adjacent to it, 1.550(22) for the central bonds in the bridges and 1.548(16) Å for the bonds originating from the singular bridgehead] all can be explained in terms of the features of this cage hydrocarbon. All three CCC valence angles [113.0(8)° at the singular bridgehead, 112.8(12) adjacent to it and 122.3(20) adjacent to the skeletal cyclopropane ring] are larger than the regular tetrahedral angle on an sp3-hybridized carbon atom. The two-carbon bridges between the skeletal cyclopropane ring and the opposite bridgehead are twisted with a dihedral angle of 43(2)°, i.e. significantly less than the approximately 60° in n-butane in its synclinal (gauche) conformation.