Raman, infrared and NMR spectra and structure of divinylmethylborane

The Raman spectra of gaseous, liquid and solid divinylmethylborane have been recorded from 20-3500 cm-1 and the IR spectra of gaseous and solid divinylmehtylborane recorded over the range 30-3500 cm-1. A variable temperature study of the Raman spectrum of the liquid phase has been carried out. A complete vibrational assignment is presented. In the solid phase the molecule appears to have a planar heavy atom skeleton (Csub(s) symmetry). From analaysis of the spectra of the fluid phases, the presence of a second isomer, in which one or both of the vinyl groups are twisted slightly out of the BC, plane (C1 symmetry), is proposed. Variable temperature 13C NMR studies have been carried out. A comparison of the 13C chemical shift of Csub(β) of the vinyl group with the corresponding value in other vinylboranes indicates that relatively little delocalization of the π-electron density occurs in this molecule. Low temperature (-1150C) 13C NMR data are consistent with a low barrier to rotation about the boron-vinyl carbon bond. (orig.)