Abstract
The IR (3200-80 cm −1) spectra have been recorded for gaseous and solid ethyldimethylamine-borane, CH 3CH 2(CH 3) 2N(BH 3), and its deuterated analogue, CH 3CH 2(CH 3) 2N(BD 3). Additionally, the Raman (3200-10 cm −1) spectra have been recorded for the liquid and solid phases, with qualitative depolarization values being obtained from the liquid. Based on the disappearance of several bands on going from the gas or liquid to the solid, it is concluded that the molecule exists as a mixture of the trans and gauche conformers in the fluid phases, but only the gauche conformer is present in the solid. From a variable temperature Raman study of the liquid the ethalpy difference is estimated to be 113±150 cm −1 (323±429 cal mol −1). A complete vibrational assignment is proposed for the gauche conformer based on group frequencies, isotopic shift data, and relative intensities. The assignment is supported by a normal coordinate calculation which was carried out utilizing a modified valence force field to calculate the frequencies of the normal modes and the potential energy distribution. The asymmetric torsion has been assigned to the bands at 130 and 124 cm −1 in the d 0 and d 3 compounds, respectively. These results are compared with corresponding results for several other amine-boranes and phosphine-boranes.
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