Microwave spectrum of o-benzyne produced in a discharge nozzle

摘要

The microwave spectrum for o-benzyne was obtained by passing a dilute (<1%) mixture of benzene in neon through a pulsed-DC discharge nozzle source into a pules-beam, Fourier transform spectrometer. Rotational transitions were measured for the normal isotopomer, the two unique single-D isotopomers, and the all-~13C isotopomer and one of the single- ~13C isotopomers. Benzynes have been known as reactive intermediates in organic reactions for many years, and have recently been implicated in gasoline combustion reactions and antitumor activity of enediynes. Twenty-seven b-type transitions for the normal isotopomer were fit to obtain A=6989.7292(6), B=5706.8062(6), and C=3140.3708(4) MHz, and five centrifugal distortion constants. The inertial defect is triangle open =0.0694 amu A~2, consistent with a planar struture. Hyperfine structure for the D_1(closest to the c=c bond) and D_2(furthest from the C=C bond), was analyzed to botain deuterium quadrupole coupling strengths eQq_aa(D_1)=185(3) kHz eQq-bb(D_1)=-85(2) kHz, eQq_aa(D_2)=5(13), and eQq_bb(D_2)=86(13)kHz. The C-D, bond axis quadrupole coupling strengths are compared with values for benzene. Spectra for the ~13C_6 and one of the ~13C_1 isotopomers were analyzed to obtain rotational constants. Kraitchman analysis and least-squares fitting provided nearly all of the structural parameters. The preliminary structural analysis yields an acetylenic c=c bond length of 1.24 A, in agreement with a recent NMR value. Density functional theory calculations were used to obtain structural parameters, and values obtained are in very good agreement with present experimental results.