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Raman, infrared and NMR spectra, conformational stability and ab initio calculations of trimethoxyborane
Author(s) -
Stampf E. J.,
Kim Young H.,
Durig J. R.
Publication year - 1993
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1250241103
Subject(s) - raman spectroscopy , chemistry , ab initio , ab initio quantum chemistry methods , basis set , infrared , spectral line , infrared spectroscopy , nmr spectra database , molecular physics , potential energy , computational chemistry , molecule , atomic physics , density functional theory , physics , organic chemistry , astronomy , optics
The Raman spectra (3500–20 cm −1 ) of gaseous, liquid and solid and the infrared spectra (4000–50 cm −1 ) of gaseous and solid trimethoxyborane, B(OCH) 3 , were recorded. Qualitative depolarization values were obtained from the Raman spectrum of the liquid. All normal modes, except the torsions, were assigned based on infrared band contours, depolarization values, group frequencies and normal coordinate calculations. From a comparison of the spectra in the fluid states with that from the solid, 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 were calculated with the force constants obtained from ab initio calculations with the 3–21G basis set. A comparison of these calculated frequencies with the observed spectra is consistent with the predominant form having a ‘planar’ heavy atom skeleton with C 3 h symmetry. In was not possible to determine an experimental barrier to rotation about the BO bond. No change was observed in the 13 C NMR spectrum over the temperature range of 22 to −90°C. Structural parameters, conformational stability and barriers to internal rotation were obtained from ab initio Hartree–Fock gradient calculations employing both the 3–21G and 6–31G* basis sets. The results are compared with the corresponding data for some similar organoboranes.