Raman, infrared and NMR spectra and structure of divinylmethylborane

Abstract

The Rarnan spectra of gaseous, liquid and solid divinylmethylborane have been recorded from 20–3500 cm −1 and the IR spectra of gaseous and solid divinylmethylborane 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 ( C s symmetry). From analysis 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 3 plane ( C 1 symmetry), is proposed. Variable temperature 13C NMR studies have been carried out. A comparison of the 13C chemical shift of C 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 (−115°C) 13C NMR data are consistent with a low barrier to rotation about the boron-vinyl carbon bond.