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D. L. FIACCO, S. W. HUNT AND K. R. LEOPOLD, Department of Chemistry, University of Minnesota, Minneapolis, MN 55455.
The donor-acceptor complexes F3B-N(CH3)3 and (CH3)3B-N(CH3)3 have been studied by Fourier transform microwave spectroscopy. The rotational constants for both species are consistent with the literature values. For F3B-N(CH3)3, the J = 0 - 1 and 1 - 2 transitions have been fully analyzed for the 10B, 11B, 14N and 15N species. A single state is observed, with no evidence of internal rotation. For (CH3)3B-N(CH3)3, the 0-1 and 1-2 transitions have been recorded and analyzed. In this case, two states are observed, with an intensity ratio of about 10:1. For both systems, a Townes and Dailey analysis of the 14N nuclear quadrupole coupling constants has been used to provide information about the electronic structure of the complexes. In the case of F3B-N(CH3)3, about 0.6 electrons are transferred from the trimethylamine to the BF3 upon formation of the donor-acceptor bond, while for (CH3)3B-N(CH3)3 a value of 0.42 electrons is obtained. These results will be compared with similar measurements for related adducts of ammonia and trimethylamine.