AN ELECTRON-DIFFRACTION, AB-INITIO AND VIBRATIONAL SPECTROSCOPIC STUDY OF 1,2-DI-TERT-BUTYLDISILANE

The molecular structure of 1,2-di-tert-butyldisilane has been accurate ly determined by gas-phase electron diffraction (GED) and ab initio ca lculations. These techniques show that the large majority of molecules at room temperature have the anti conformation with overall symmetry C-2, and vibrational spectra confirm this conclusion, Infrared spectra of the gas and liquid phases, and Raman spectra of the liquid and sol id phases, have been recorded for (CH3)(3)CSiH2SiH2C(CH3)(3) and (CH3) (3)CSiD2SiD2C(CH3)(3). The most striking feature of this structure (r( a)) is a relatively large deviation of the SiSiC angle from the parent tetrahedral angle 109.5 degrees (113.7(3)degrees, GED; 114.4 degrees, SCF/6-31G as calculated for the anti form). That the Si-Si bond leng th does not show any substantial deviation from its usual value (234.8 (3) pm, GED; 236.8 pm, SCF/6-31G computed for the anti form) is also substantiated by the value of the SiSi valence force constant (169 N m (-1)) given by normal coordinate analysis. The t-butyl groups are tilt ed so that the SI-C bonds (GED (SCF/6-31G): 190.1(1) (191.9)pm) do no t coincide with the local C-3 axes of the C(CH3)(3) groups in which th e C-C bond length is 154.1(1) (GED); 154.0 (SCF/6-31G) pm. The confor mations along all the single bonds are more or less staggered.