Semiexperimental Equilibrium Structure for the C6 Backbone of cis-1,3,5-Hexatriene; Structural Evidence for Greater π-Electron Delocalization with Increasing Chain Length in Pol

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• 作者：Richard D. Suenram^† ; ; Brooks H. Pate^† ; ; Alberto Lesarri^‡ ; ; Justin L. Neill^† ; ; Steven Shipman^† ; ; Robin A. Holmes^
• 刊名：Journal of Physical Chemistry A
• 出版年：2009
• 出版时间：March 5, 2009
• 年：2009
• 卷：113
• 期：9
• 页码：1864-1868
• 全文大小：123K
• 年卷期：v.113,no.9(March 5, 2009)
• ISSN：1520-5215

文摘

Twenty-five microwave lines were observed for cis-1,3,5-hexatriene (0.05 D dipole moment) and a smaller number for its three ¹³C isotopomers in natural abundance. Ground-state rotational constants were fitted for all four species to a Watson-type rotational Hamiltonian for an asymmetric top (κ = −0.9768). Vibration−rotation (alpha) constants were predicted with a B3LYP/cc-pVTZ model and used to adjust the ground-state rotational constants to equilibrium rotational constants. The small inertial defect for cis-hexatriene shows that the molecule is planar, despite significant H−H repulsion. The substitution method was applied to the equilibrium rotational constants to give a semiexperimental equilibrium structure for the C₆ backbone. This structure and one predicted with the B3LYP/cc-pVTZ model show structural evidence for increased π-electron delocalization in comparison with butadiene, the first member of the polyene series.