title: Microwave spectra of the deuterium isotopologues of cis-hexatriene and a semiexperimental equilibrium structure.
abstract: Microwave transitions and ground state rotational constants are reported for five newly synthesized deuterium isotopologues of cis-1,3,5-hexatriene (cHTE). These rotational constants along with those of the parent and the three (13)C species are used with vibration-rotation constants calculated from an MP2/cc-pVTZ model to derive an equilibrium structure. That structure is improved by the mixed estimation method. In this method, internal coordinates from good-quality quantum chemical calculations (with appropriate uncertainties) are fit simultaneously with moments of inertia of the full set of isotopologues. The new structure of cHTE is confirmed to be planar and is stabilized by an interaction between the hydrogen atoms H2 and H5, which form a bond and participate in a six-membered ring. cHTE shows larger structural effects of π-electron delocalization than does butadiene with the effects being magnified in the center of the molecule. Thus, strong structural evidence now exists for an increase in π-electron delocalization as the polyene chain lengthens.
authors.affiliation: Department of Chemistry and Biochemistry, Oberlin College , Oberlin, Ohio 44074, United States.
authors.forename: Norman C
authors.initials: NC
authors.lastname: Craig
authors.forename: Yihui
authors.initials: Y
authors.lastname: Chen
authors.forename: Hannah A
authors.initials: HA
authors.lastname: Fuson
authors.forename: Hengfeng
authors.initials: H
authors.lastname: Tian
authors.forename: Herman
authors.initials: H
authors.lastname: van Besien
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Conrad
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Tubergen
authors.forename: Heinz Dieter
authors.initials: HD
authors.lastname: Rudolph
authors.forename: Jean
authors.initials: J
authors.lastname: Demaison
mesh_terms: D002070:Butadienes / Q000737:chemistry; D003903:Deuterium / Q000737:chemistry*; D004583:Electrons; D006859:Hydrogen / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008872:Microwaves; D008956:Models, Chemical; D015394:Molecular Structure; D011090:Polyenes / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D012399:Rotation; D013057:Spectrum Analysis; D014732:Vibration
chemical_list: D002070:Butadienes; D011090:Polyenes; C512191:1,3,5-hexatriene; D006859:Hydrogen; D003903:Deuterium; C031763:1,3-butadiene