Microwave Spectrum, Structural Parameters, and Quadrupole Coupling for 1,2-Dihydro-1,2-azaborine

摘要

The first microwave spectrum for 1,2-dihydro-1,2-azaborine has been measured in the frequencynrange 7-18 GHz, providing accurate rotational constants and nitrogen and boron quadrupole couplingnstrengths for three isotopomers, H6C4n11B14N, H6C4n10B14N, and H5DC4n11B14N. The measured rotationalnconstants were used to accurately determine coordinates for the substituted atoms and provide sufficientndata to determine most of the important structural parameters for this molecule. The spectra were obtainednusing a pulsed beam Fourier transform microwave spectrometer, with sufficient resolution to allow accuratenmeasurements of 14N, 11B, and 10B nuclear quadrupole hyperfine interactions. High-level ab initio calculationsnprovided structural parameters and quadrupole coupling strengths that are in very good agreement withnmeasured values. The rotational constants for the parent compound are A ) 5657.335(1), B ) 5349.2807(5),nand C ) 2749.1281(4) MHz, yielding the inertial defect Δ0 ) 0.02 amu·Å2 for the ground-state structure.nThe observed near-zero and positive inertial defect clearly indicates that the molecular structure of 1,2-ndihydro-1,2-azaborine is planar. The least-squares fit analysis to determine the azaborine ring structurenyielded the experimental bond lengths and 2σ errors R(B-N) ) 1.45(3) Å, R(B-C) ) 1.51(1) Å, and R(N-C)n) 1.37(3) Å for the ground-state structure. Interbond angles for the ring were also determined. An extendednTownes-Dailey population analysis of the boron and nitrogen quadrupole coupling constants provided thenvalence p-electron occupancy pc ) 0.3e for boron and pc ) 1.3e for nitrogen.