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 Polyenes
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.
Suenram, R.D., B.H. Pate, A. Lesarri, J.L. Neill, S. Shipman, R.A. Holmes, M.C. Leyden, and N.C. Craig. 2009. "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 Polyenes." Journal of Physical Chemistry A 113(9): 1864-1868.
American Chemical Society
Journal of Physical Chemistry A
Chemistry and Biochemistry