Infrared,Raman and NMR spectra,conformational stability,and ab initio calculations of divinylmethoxyborane

The infrared spectra (4000–50 cm^?1) of gaseous and solid divinylmethoxyborane, (CH₂=CH)₂BOCH₃, as well as the Raman spectra (3500–20 cm^?1) of the liquid and solid have been recorded. Qualitative depolarization values have been obtained from the Raman spectrum of the liquid. All normal modes, except the torsions, have been assigned based on infrared band contours, depolarization values, group frequencies, and normal coordinate calculations. From a comparison of the spectra in the fluid and solid states, it is concluded that the molecule exists predominantly in a single conformation in all physical states. Frequencies and potential energy distributions for the normal modes have been calculated with the 3–21G basis set. A comparison of these calculated frequencies to the observed spectra is consistent with the predominant form having a “planar” heavy atom skeleton with C_s, symmetry. From the variable low temperature ¹³C NMR data, a barrier to rotation about the B-O bond of 10.1 ± 0.1 kcal mol^?1 has been determined, which is in excellent agreement with a barrier of 8.5 kcal mol"1 obtained from ab initio calculations. Structural parameters, conformational stability, and barriers to internal rotation have been obtained from ab initio Hartree-Fock gradient calculations employing both the 3–21G and 6–31G^* basis sets. The results are compared to the corresponding data for some similar organoboranes.