THE MOLECULAR STRUCTURES OF 1,2-DISELENIN AND 2-SELENATHIIN

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2001

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Ohio State University

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The rotational spectra of the 1,2-dichaicogenins, 1,2-diselenin and 2-selenathiin, were obtained with a pulsed-beam Fourier-transform microwave spectrometer. The least squares fit of the observed $\mu_{b}$-type transitions of the $^{80}Se^{80}Se$ isotopomer of 1,2-diselenin to a semi rigid Watson Hamiltonian gave rotational constants of A = 2081.4262(9) MHz, B = 1659.1768(9) MHz and C = 1003.0117(4) MHz. Nuclear spin statistical weights, the presence of only $\mu_{b}$-type transitions, and a large inertial defect of $\Delta = -43.5389 u\cdot \AA^{2}$ show 1,2-diselenin has $C_{2}$ symmetry. The six-member ring, $CH=CH-CH=CH-Se-Se$, is twisted about the Se-Se bond and substitution coordinates obtained from the $^{78}Se^{80}Se$ and $^{80}Se^{80}Se$ isotopic moments of inertia give a Se-Se bond distance of 2.325(3) \AA. An analogous fit of the observed $\mu_{a}$- and $\mu_{b}$-type transitions of the $^{80}Se^{32}S$ isotopomer of 2-selenathiin gave rotational constants of A = 2983.8426(6) MHz, B = 2056.7288(6) MHz and C = 1325.1405(2) MHz. The large inertial defect $\Delta = -33.7140 u\cdot \AA^{2}$ shows the ring of 2-selenathiin, $CH=CH-CH=CH-Se-S$, is not planar. An $r_{s}$ Se-S bond distance of 2.205(16) \AA is calculated from substitution coordinates obtained from the $^{80}Se^{32}S$, $^{78}Se^{32}S$, and $^{80}Se^{34}S$ isotopic moments of inertia. The structural parameters derived from the spectroscopic data will be compared to ab initio geometries of the 1,2-dichalcogenins.

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Author Institution: Siena College; Department of Chemistry, Rensselaer Polytechnic Institute; Department of Chemistry, Rensselaer Polytechnic Institute

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