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The Raman spectra (3500-20 cm-') of gaseous, liquid and solid and the infrared spectra (4000-50 cm-') of gaseous and solid trimethoxyborane, B(OCH), , 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 3-216 hasis 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,, symmetry. It was not possible to determine an experimental barrier to rotation about the B-0 bond. No change was observed in the 13C 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 HartreeFock gradient calculations employing both the 3-21G and 6-31G* basis sets. The results are compared with the corresponding data for some similar organoboranes.

The 'H, llB, 19F, and ,lP NMR spectra of B4H8PF2N(CH,), indicate that the compound exists as two isomers in solution. Low-temperature 19F NMR spectra demonstrate that these isomers are geometrical in nature. At low temperatures (-125 "C) rotation about the P-B bond in one isomer becomes slow on the experimental time scale, while this rotation remains rapid in the second isomer. Spectral simulations yield a AG* value of 7.8 kcal/mol for the barrier to rotation about the P-B bond in one of the geometrical isomers. At high temperature (80 "C) the two geometrical isomers interconvert rapidly on the 19F NMR time scale. Simulations of the high-temperature spectra yield a AG* value of 19 kcal/mol for the barrier to interconversion of these isomers. This value and other data including isotopic labeling studies are discussed in terms of the mechanism by which the geometrical isomers interconvert at high temperature. IntroductionThe existence of isomers in the B4H8PF2N(CHJ2 molecule was established on the basis of the presence of two doublets in the I9F NMR s p e~t r u m .~ The doublets were found to reversibly coalesce to a single doublet at high temperature and the isomers were described as geometrical in nature, orginating from endo and exo orientation of the ligand with respect to the folded B4 ring. In the same report3 no evidence was observed for the presence of isomers in B4H8PF2H. Inter-

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