A double-minimum skeletal torsion in 1-silabicyclo[2.2.2]octane by microwave spectroscopy

Abstract

The 1-silabicyclo[2.2.2]octane molecule HSi(CH 2CH 2) 3CH was investigated by microwave spectroscopy. The observed spectra followed the symmetric-rotor pattern with the unresolved K structures, but were accompanied by many strong vibrational satellites. A series of the prominent satellites was assigned to the excited states of the skeletal torsion. The transition frequencies and the relative intensities which were measured for the satellites were used to determine the double-minimum potential function to the skeletal torsion. The height of the potential hump and the equilibrium torsional angle, which was defined as the SiCCC dihedral angle, were determined to be 606 ± 40 cal/mole and 21.3° ± 1.0°, respectively. The results that the double-minimum nature of the potential function is more pronounced in 1-silabicyclo[2.2.2]octane than in other bicyclo[2.2.2]octane derivatives studied previously are discussed in detail in terms of the internal-rotation potential around the CC and CSi bonds and the strains in the valence angles of the C and Si atoms.