THE MOLECULAR-STRUCTURES OF 1,1-DIMETHYLSILACYCLOBUTANE AND 1,1,3,3-TETRAMETHYL-1,3-DISILACYCLOBUTANE AS DETERMINED BY GAS-PHASE ELECTRON-DIFFRACTION

The molecular structures of 1,1-dimethylsilacyclobutane (DMSICB) and 1,1,3,3-tetramethyl-1,3-disilacyclobutane (TMDSICB) have been studied by gas-phase electron diffraction at room temperature. Both molecules exist in a puckered conformation. The major geometrical parameters obtained are as follows: for DMSICB, r(C-H) = 1.117(4) angstrom, r(C-C) = 1.565(4) angstrom, r(Si-C)av = 1.880(2) angstrom, Delt(Si-C) = [r(Si-C)-r(Si-C(m))] = 0.004(15) angstrom, angle CSiC = 76.6(0.8)-degrees, angle C(m)SiC(m) = 113(2)-degrees, angle HCSi = 113.5(1.6)-degrees, angle HCH = 111(4)-degrees, and Flap [angle between the planes formed by atoms C1, Si, C3 and C1, C2, C3, where planar = 34.2(3.0)-degrees; for TMDSICB, r(C-H) = 1.080(5) angstrom, r(Si-C)av = 1.884(2) angstrom, Delt(Si-C) = 0.017(3) angstrom, angle CSiC = 90.1(6)-degrees, angle C(m)SiC(m) = 117.4(2.6)-degrees, angle HCSi = 112.5(1.7)-degrees, and Flap = 22.1(2.2)-degrees.