1. Analysis of the Rotational Structure in the High-Resolution Infrared Spectrum of trans-Hexatriene-1,1-d 2 and -cis-1-d 1 Norman C. Craig, Hannah A. Fuson, and Hengfeng Tian Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074, USA Norm.Craig@oberlin.eduNorm.Craig@oberlin.edu Thomas A. Blake Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352

2. Goal Do the isomers of hexatriene (HTE) show greater structural effects of  -electron delocalization than does butadiene? Preliminary data for the C 6 backbone of cis-HTE say “Yes,” as do B3LYP calculations with a cc-pVTZ basis set. New work: analysis of C-type bands in high-resolution IR spectra of trans-HTE-1,1-d 2 and -cis-1-d 1.

3. Method: Semi-Experimental Equilibrium Structure Obtain ground state rotational constants from the rotational structure in high-resolution IR bands. (Nonpolar trans-HTE is MW silent.) Do so for a full series of isotopologues. Use quantum chemistry (triple zeta level) to compute vibration-rotation constants (alphas). Find equilibrium rotational constants (k = a,b,c) Obtain an r e structure from a global fit of all the equilibrium rotational constants.

4. Synthesis

5. IR spectrum (0.1 cm -1 resol.) of trans-HTE-1,1-d 2 and -cis-1-d 1 d2d2 d2d2 d2d2 d1d1

6. C-Type Bands Analyzed tHTE-1,1-d 2 29 (902 cm -1 ) CH 2 out-of-plane flapping 31 (722 cm -1 ) CD 2 out-of-plane flapping tHTE-cis-1-d 1 31 (803 cm -1 ) CD out-of-plane flapping

7. C-type Band (0.0015 cm -1 resol.) of trans-HTE-1,1-d 2

8. Detail of C-type Band at 902 cm -1 of trans-HTE-1,1-d 2

9. Finer Detail of C-type Band at 902 cm -1

10. C-type Band (0.0015 cm -1 resol.) of trans-HTE-1,1-d 2

11. Rotational Constants for trans-Hexatriene-1,1-d 2

12. C-type Band (0.0015 cm -1 resol.) of trans-HTE-cis-1-d 1

13. Loomis-Wood Display for C-type Band of trans-Hexatriene-cis-1-d 1 R R 13 yellow R R 16 blue R R 14 magenta R R 17 brown R R 15 red

14. Rotational Constants for trans-Hexatriene-cis-1-d 1

15. Conclusions Analysis of the rotational structure in the high-resolution (0.0015 cm -1 ) infrared spectrum of two C-type bands of trans-hexatriene-1,1-d 2 and of a C-type band of trans-hexatriene-cis-1-d 1 has yielded ground state rotational constants for the two species. Prior work gave ground state rotational constants for the normal species. 1 Good progress has been made toward the rotational constants needed for a semi-experimental structure of trans-hexatriene. See the following talk. 1. N. C. Craig, M. C. Leyden,M. C. Moore, Amie K. Patchen, T. van den Heuvel, T. A. Blake, T. Masiello, R. L. Sams J. Mol. Spectrosc. 2010, 262, 49-60.

16. Support Dreyfus Foundation Environmental and Molecular Sciences Laboratory, PNNL National Science Foundation Oberlin College