MICROWAVE SPECTRUM AND DIPOLE MOMENT OF 2,3-DlAZABICYCLO(2.2.1)HEPT-2-ENE
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Date
1975
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Publisher
Ohio State University
Abstract
The extremely rich microwave spectrum of the title compound has been assigned and analyzed using a combination of conventional Stark modulation spectroscopy and radio frequency-microwave double resonance (RFMDR). The dipole moment has been measured and found to be approximately equally distributed along the a and c principal axes ($\mu_{a} = 2.76 \pm 0.01$ D and $\mu_{c} = 2.12 \pm 0.07$ D and $\mu_{t} = 3.48 \pm 0.06$ D). The microwave spectra of all the singly substituted $^{13}C$ were assigned using RFMDR on a sample containing a mixture of isotopically enriched $^{13}C$ species. This data allowed the determination by the $r_{s}$ method of several pertinent structural parameters associated with the carbon atom ring: $C_{5} - C_{6} = 1.552 \pm 0.002 {\AA}, C_{1} - C_{4} = 2.194 \pm 0.002 {\AA}, C_{1} - C_{7} = 1.533 \pm 0.005 {\AA}, \angle C_{1} - C_{7}- C_{4} = 91.3 \pm 0.5 {\AA}, \angle C_{1} - C_{4} - C_{5} = 78 \pm 1{\AA}$. The corresponding values from a previous electron diffraction study are: $^{1}$ $C_{5} - C_{6} - 1.530 {\AA}, C_{1} - C_{4} - 2.50 {\AA}, \angle C_{1} - C_{7} = 1.547 {\AA}, \angle C_{1} - C_{7} - C_{4} = 108.0^\circ C_{1} - C_{4} - C_{5} - 71.5^\circ$. A small value for the a-coordinate ($\sim$ 0.03 {\AA}) of $C_{1}$ (and $C_{4}$ by symmetry) precludes the determination of some of the parameters, by the $r_{s}$ method, namely the $C_{1}-C_{6}$ bond length and several angles involving $C_{1}$. The determination of these parameters will be discussed as well as the discrepancies between the microwave and electron diffraction results. Qualitative measurements of the relative intensities of the $^{13}C$ species and the small value of the inertial defect for the $7-^{13}C$ species indicate that the molecule possesses $C_{s}$ symmetry.
Description
$^{1}$ J. F. Chiang, R. L. Chiang, and M. T. Kratus, J. Mol. Struct., to be published.""
Author Institution: Department of Chemistry, Harvard University
Author Institution: Department of Chemistry, Harvard University