The Molecular Structure of gauche‐1,3‐Butadiene: Experimental Establishment of Non‐planarity |
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| Authors: | Dr. Joshua H. Baraban Dr. Marie‐Aline Martin‐Drumel P. Bryan Changala Dr. Sandra Eibenberger Dr. Matthew Nava Prof. David Patterson Prof. John F. Stanton Prof. G. Barney Ellison Dr. Michael C. McCarthy |
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| Affiliation: | 1. Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, USA;2. Current address: Dept. of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel;3. Harvard-Smithsonian Center for Astrophysics and School of Engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts, USA;4. Current address: Institut des Sciences Moléculaires d'Orsay, CNRS, Univ. Paris-Sud, Université Paris-Saclay, Orsay, France;5. JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, CO, USA;6. Department of Physics, Harvard University, Cambridge, MA, USA;7. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA;8. Current address: Department of Chemistry, Harvard University, Cambridge, MA, USA;9. Current address: Department of Physics, University of California, Santa Barbara, CA, USA;10. Quantum Theory Project, Depts. of Chemistry and Physics, Univ. of Florida, Gainesville, FL, USA |
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| Abstract: | The planarity of the second stable conformer of 1,3‐butadiene, the archetypal diene for the Diels–Alder reaction in which a planar conjugated diene and a dienophile combine to form a ring, is not established. The most recent high level calculations predicted the species to adopt a twisted, gauche structure owing to steric interactions between the inner terminal hydrogens rather than a planar, cis structure favored by the conjugation of the double bonds. The structure cis‐1,3‐butadiene is unambiguously confirmed experimentally to indeed be gauche with a substantial dihedral angle of 34°, in excellent agreement with theory. Observation of two tunneling components indicates that the molecule undergoes facile interconversion between two equivalent enantiomeric forms. Comparison of experimentally determined structures for gauche‐ and trans‐butadiene provides an opportunity to examine the effects of conjugation and steric interactions. |
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| Keywords: | ab initio calculations butadiene conjugation molecular dynamics rotational spectroscopy |
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