MICROWAVE SPECTRUM, STRUCTURAL PARAMETERS AND QUADRUPOLE COUPLING FOR AZABORINE AND 1-ETHYL-AZABORINE

Supported by THE NATIONAL SCIENCE FOUNDATIONAuthor Institution: Department of Chemistry and Biochemistry, The University of Arizona, Tucson, Arizona 85721.; Department of Chemistry and Physics, Arkansas State University, Jonesboro, AR 72467; Department of Chemistry, University of Oregon, Eugene, OR 97403\begin{wrapfigure}[11]{R}{3.0CM} \vspace{-1.2cm} \hspace*{-0.4cm} \epsfig{file=azb1.eps} \end{wrapfigure} The first microwave spectra for the unusual and elusive aromatic molecules, 1,2-dihydro-1,2-azaborine (azaborine) and 1-ethyl-azaborine have been measured, in the 7-18 GHz range, providing accurate rotational constants, nitrogen and boron quadrupole coupling strengths, important bond lengths and other structural parameters. Azaborine (BNC$_4$H$_6$)is an aromatic, B-N substituted analog of benzene, the quintessential aromatic molecule. The experimental bond lengths determined for azaborine are: R(B-N) = 1.45(3) \AA, R(B-C) = 1.51(1) \AA, and R(N-C) = 1.37(3) \AA. Accurate measurements of $^{14}$N, $^{11}$B, and $^{10}$B nuclear quadrupole coupling were obtained. The inertial defect $\Delta$ = 0.02 amu \AA$^2$ indicating a planar structure. A Townes-Dailey population analysis of the B and N quadrupole coupling constants provided the valence p-electron occupanc