DETERMINATION BY ELECTRON-DIFFRACTION OF THE MOLECULAR-STRUCTURE OF BROMOTRIS(METHOXYDIMETHYLSILYL)METHANE IN THE GAS-PHASE

The molecular structure of bromotris(methoxydimethylsilyl) methane in the gas phase has been determined by electron diffraction. The molecul es have C, symmetry, adopting a conformation in which the Si-O bonds a re gauche with respect to the C-Br bond, and the O-C bonds are anti wi th respect to the inner Si-C bonds. This arrangement avoids conflict b etween the sterically demanding methoxydimethylsilyl groups and minimi ses interactions between lone pairs of electrons on the methoxy groups , which are widely separated from each other, on the periphery of the molecule. The Br-C-Si-O and C-inner-Si-O-C dihedral angles are 38.5(5) and 169.9(28)degrees respectively. Other principal parameters (r(a)) are r(C-Br) 196.0(21) pm, r(Si-C-inner) 190.6(10) pm, r(Si-C-outer) 18 8.3(4) pm, r(Si-O) 167.4(4) pm, r(O-C) 141.9(5) pm, and angles Br-C-Si 106.2(6)degrees, C-inner-Si-C-outer 114.7(5)degrees, C-inner-Si-O 107 .3(9)degrees, C-outer-Si-O 106.4(8)degrees and Si-O-C 121.4(13)degrees .