Microwave spectra, molecular structure and aromatic character of BN-Naphthalene (4A,8A-Azaboranaphthalene)

Abstract

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.36]{BN-nap1.eps} \end{wrapfigure} The microwave spectra for seven unique isotopologues of BN-naphthalene (4a,8a-azaboranaphthalene) were measured using a pulsed-beam Fourier transform microwave spectrometer. Spectra were obtained for the normal isotopologues with $^{10}$B, $^{11}$B, all unique single $^{13}$C and the $^{15}$N isotopologue, in natural abundance. The rotational, centrifugal distortion and quadrupole coupling constants determined for the $^{11}$B$^{14}$N isotopologue are A = 3042.7128(4) MHz, B = 1202.7066(4) MHz, C = 862.2201(4) MHz, D$_{J}$ = 0.06(1) kHz, 1.5 eQq$_{aa}$ ($^{14}$N) = 2.578(6) MHz, 0.25(eQq$_{bb}$- eQq$_{cc}$) ($^{14}$N) = -0.119(2) MHz, 1.5 eQq$_{aa}$ ($^{11}$B) = -3.922(8) MHz, and 0.25(eQq$_{bb}$- eQq$_{cc}$) ($^{11}$B) = -0.907(2) MHz. The experimental inertial defect is $\Delta$ = -0.159 amu \AA$^{2}$, which is consistent with a planar structure. The B-N bond length is 1.47 \AA, indicating $\pi$-bonding character. The results are compared with similar results for B-N bonding in 1,2-dihydro-1,2-azaborine and BN-cyclohexene.