The Raman, ultraviolet, and infrared spectra and the J_Si=C NMR coupling constant of the stable silence (t-BuMe₂Si)(Me₃Si)Si=2-Ad. Manifestations of the Si=C double bond

The UV, preresonance Raman, and IR spectra of the stable silene t-BuMe₂Si(Me₃Si)Si=2-Ad (1) have been measured as well as its J_Si=C NMR coupling constant. The normal modes involving the v(Si=C) stretching coordinate were identified for the first time for a stable silene. The experimental data and computations of potential energy distribution and mode eigenvectors show that there is no single vibrational normal mode which can be assigned as v(Si=C). Raman intensity enhancement on approaching resonance strongly supports the conclusion that there are five lines in the region 1000-1370 cm^-1 which include significant contribution from the v(Si=C) stretching coordinate. Both the Si=C force constant and the J_Si=C NMR coupling constant (as well as the Si=C bond length) indicate that the Si=C bond order is smaller in 1 than that in simpler silenes of the type R₂Si=CH₂ (R = H, Me).