20815-44-5Relevant academic research and scientific papers
Conformational studies by dynamic NMR, Part 68 [?] correlated rotation of the Me3Si groups in tris(trimethylsilyl)methanes
Casarini, Daniele,Foresti, Elisabetta,Lunazzi, Lodovico,Mazzanti, Andrea
, p. 3501 - 3508 (2007/10/03)
Low-temperature NMR spectra of (Me3Si)3CH (1) allowed the restricted rotation of the Me3Si groups to be detected; the barrier was 5.1 kcal mol-1. On the basis of molecular mechanics calculations, this motion was assigned to a correlated disrotatory process with an eclipsed, staggered, staggered (ESS) transition state. In (Me3Si)3CMe (2), both a correlated ESS disrotatory process and a correlated conrotatory SSS process were distinguished, with rotational barriers of 6.7 and 5.15 kcal mol-1, respectively. Thus, 2 appears to adopt a chiral conformation (point group C3) at low temperature. For more hindered derivatives such as (Me3Si)3CCH2Me (3) and (Me3Si)3C-CH2Et (4), the ESS and SSS processes involving rotation about the Si-C bonds were also detected, but in addition a third process became evident. This process corresponds to restricted rotation about the C-C bond and seems to be correlated with the SSS conrotatory process at the C-Si bond, since both display essentially the same barrier. Although in (Me3Si)3CCH2Ph (5) the effects of restricted rotation about the C-CH2Ph bond could not be observed, the same chiral conformation adopted by 3 and 4 (point group C1) was nonetheless assigned on the basis of molecular mechanics calculations and X-ray diffraction studies. The 13C spectra (CP-MAS) of crystalline 5 also showed that the pairs of ortho and meta phenyl carbon atoms are diastereotopic due to restricted Ph-CH2 bond rotation in the solid state.
