Knowledge Bank

\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 $\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$N, $\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}$B, and $\mathrm{<mrow\; data-mjx-texclass="ORD">10</mrow>}$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 occupancy