SPECTROSCOPIC STUDIES OF THE CONFORMATIONS OF NORMAL-DECAMETHYLTETRASILANE

The conformational properties of n-decamethyltetrasilane, n-Si4(CH3)10, have been studied by variable temperature NMR (1H and 13C) and vibrational (IR and Raman) spectroscopy. As in related alkane systems, the anti conformer is more stable than the gauche conformer. Values of △H0 and △S0 for the anti → gauche reaction are 2.26 ± 0.15 kJ mol-1 and △S0 = 7.82± 0.86 J K-1mol-1, respectively. Thus, the two conformers are present in comparable quantities at room temperature. At very low temperatures, broadening of the two proton resonances (SiMe2, SiMe3) occurs, but phase changes precluded the observation of decoalescence. By approximate lineshape anaylysis, the free energy of activation, △G‡, for rotation about the central SiSi bond is estimated to be ∼25 kJ mol-1. © 1979.