STRUCTURE OF 1-METHYL-1-SILAADAMANTANE AS DETERMINED BY GAS-PHASE ELECTRON-DIFFRACTION

The structure of 1-methyl-1-silaadamantane (MSA) has been determined by gas phase electron diffraction. There appears to be somewhat less ring strain at the silicon bridgehead of MSA than in the previously studied 1-methyl-1-silabicyclo[2.2.1]heptane (MSBH). The average SiC bond length [1.879(3) Å is comparable to those found in acyclic organosilicon systems. Also, the average CC bond length (1.547(2) Å) is only slightly longer than that observed for adamantane (1.540(2) Å). Valence angles at the silicon bridgehead experience only a moderate perturbation away from their unstrained tetrahedral values. On this basis it is expected that MSA should be somewhat less reactive than MSBH under SN2 conditions according to the reaction mechanism suggested by L.H. Sommer. © 1979.