EXISTENCE OF 2 DISTINCT ISOMERIC FORMS OF ME(ON)SICH2 - A THEORETICALCONFIRMATION

On the basis of the results of the experimental IR studies of matrix r eactions between methylsilanes and oxygen atoms, Withnall and Andrews have postulated the possibility of the existence of equilibrium betwee n two farms of Me(OH)Si=CH2. in order to verify their supposition, an ab initio study at various levels of theory was performed. Two hydroxy forms of methylsilaethylene were fully optimized using the gradient p rocedures at the MP2 and DFT(Becke3LYP) approximations with the standa rd 6-311G(d,p), 6-311G(2d,2p), and 6-311G(2df,2pd) basis sets. Harmoni c vibrational frequencies were calculated at all levels. The MP4-(SDQ) /6-311G(2df,2dp)parallel to MP2/6-311G(2df,2p) + ZPE(MP2) calculations establish the energy difference between cis and trans isomers at 1.9 kcal/mol, which makes both forms experimentally accessible. Vibrationa l frequencies and shifts of frequencies upon isotopic O-18 and deuteri um substitutions predicted at the MP2 and DFT levels correlate well wi th the experimental data, thus supporting assignments of vibrational b ands and identifications of reaction products by Withnall and Andrews.