Infrared and Raman spectra of trimethoxyborane isotopomers and quantum-chemical studies of structure and force field

Infrared and Raman spectra in the gas phase are reported for trimethoxyborane, B(OCH3)(3), and its C-13(3) and d(9) isotopomers. Some liquid phase Raman data were also obtained. Quantum-chemical (QC) studies of structure and force field have been made with B3LYP and MP2 models. These studies highlight the change in configuration of the methyl groups with change in basis set, within the C-3h point group. Scaled QC force fields together with the new spectra enable assignments of fundamental bands to be improved. A Fermi resonance involving nu(12) is examined. The difference in strength between the two types of C-H bond in each methyl group is reckoned to be rather less than that deduced earlier from IR spectra of B(OCHD2)(3). This conclusion is supported by QC data for dimethylether. MP2 estimates of certain interaction force constants are superior to those from B3LYP calculations. Abnormal scale factors for the torsional motion involving the O-B-O-C system identify deficiencies in the QC models employed. (C) 2010 Elsevier B.V. All rights reserved.