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.
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.
Suenram
Richard D
RD
Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, USA.
Pate
Brooks H
BH
Lesarri
Alberto
A
Neill
Justin L
JL
Shipman
Steven
S
Holmes
Robin A
RA
Leyden
Matthew C
MC
Craig
Norman C
NC
D004583:Electrons; D007536:Isomerism; D008872:Microwaves; D015394:Molecular Structure; D011090:Polyenes / Q000737:chemistry*; D012399:Rotation; D013057:Spectrum Analysis; D014732:Vibration
D011090:Polyenes; C512191:1,3,5-hexatriene