1. Ab Initio Structures for 90°-Twisted s-trans-1,3-Butadiene and Cyclooctatetraene; the Naked sp2-sp2 Bond and Other Disclosures about Equilibrium Structures of Butadiene
David Feller, Department of Chemistry, Washington State University, Pullman, WA 99164
Norman C. Craig and Albert R. Matlin, Department of Chemistry and Biochemistry, Oberlin College, Oberlin, OH 44074

2. Outline
Structures of various 1,3-butadiene rotamers from ab initio calculations.
Lengths of the naked sp2-sp2 single bond and the localized C=C bond.
Comparison with the structure of cyclooctatetraene from ab initio calculations.
Comparison with the structure of a dimer of butadiene ([4]-dendralene) from electron diffraction.

5. Method for ab initio Calculations
CCSD(T)/aug-cc-pVnZ, n = 2,3,4. Frozen core.
Complete basis set extrapolation of the geometric parameters.
Corrections for core/valence effects with CCSD(T)/cc-pCVQZ applied to geometric parameters.
Corrections for scalar relativistic effects from Douglas-Kroll-Hess CCSD(T)/cc-pVTZ_DK calculations applied to geometric parameters.

8. Boat form of cyclooctatetraene
90°-twisted butadiene
Boat form of cyclooctatetraene

10. [4]Dendralene Dimer of 1,3-Butadiene
Dihedral angle = 71.7°; r(C3-C4) = Å (long).a
Compare sp2-sp3 bond length in propene = Å.b
a Electron diffraction: P. T. Brain, B. A. Smart, H. E. Robertson, D. W. H. Rankin, W. J. Henry, I. Gosney, J. Org. Chem. 1997, 62,
b Equil. struct.: J. Demaison, H. D. Rudolph, J. Mol. Spectrosc. 2008, 248,

12. Funding National Science Foundation (Beowulf cluster supercomputer)
Dreyfus Foundation
Department of Chemistry and Biochemistry, Oberlin College

14. Comparison of re Structures of Butadiene and Propene