title: Semiexperimental equilibrium structure for the C6 backbone of cis-1,3,5-hexatriene; structural evidence for greater pi-electron delocalization with increasing chain length in polyenes.
abstract: Twenty-five microwave lines were observed for cis-1,3,5-hexatriene (0.05 D dipole moment) and a smaller number for its three (13)C isotopomers in natural abundance. Ground-state rotational constants were fitted for all four species to a Watson-type rotational Hamiltonian for an asymmetric top (kappa = -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 C(6) backbone. This structure and one predicted with the B3LYP/cc-pVTZ model show structural evidence for increased pi-electron delocalization in comparison with butadiene, the first member of the polyene series.
authors.affiliation: Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Suenram
authors.forename: Brooks H
authors.initials: BH
authors.lastname: Pate
authors.forename: Alberto
authors.initials: A
authors.lastname: Lesarri
authors.forename: Justin L
authors.initials: JL
authors.lastname: Neill
authors.forename: Steven
authors.initials: S
authors.lastname: Shipman
authors.forename: Robin A
authors.initials: RA
authors.lastname: Holmes
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Leyden
authors.forename: Norman C
authors.initials: NC
authors.lastname: Craig
mesh_terms: D004583:Electrons; D007536:Isomerism; D008872:Microwaves; D015394:Molecular Structure; D011090:Polyenes / Q000737:chemistry*; D012399:Rotation; D013057:Spectrum Analysis; D014732:Vibration
chemical_list: D011090:Polyenes; C512191:1,3,5-hexatriene