The Molecular Structure of gauche-1,3-Butadiene: Experimental Establishment of Non-planarity

Joshua H Baraban; Marie-Aline Martin-Drumel; P Bryan Changala; Sandra Eibenberger; Matthew Nava; David Patterson; John F Stanton; G Barney Ellison; Michael C McCarthy

doi:10.1002/anie.201709966

The Molecular Structure of gauche-1,3-Butadiene: Experimental Establishment of Non-planarity

Angew Chem Int Ed Engl. 2018 Feb 12;57(7):1821-1825. doi: 10.1002/anie.201709966. Epub 2018 Jan 18.

Authors

Joshua H Baraban^{1

2}, Marie-Aline Martin-Drumel^{3

4}, P Bryan Changala⁵, Sandra Eibenberger⁶, Matthew Nava^{7

8}, David Patterson^{6

9}, John F Stanton¹⁰, G Barney Ellison¹, Michael C McCarthy³

Affiliations

¹ Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO, 80309, USA.
² Current address: Dept. of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel.
³ Harvard-Smithsonian Center for Astrophysics and School of Engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts, 02138, 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, 80309, USA.
⁶ Department of Physics, Harvard University, Cambridge, MA, 02138, USA.
⁷ Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139, USA.
⁸ Current address: Department of Chemistry, Harvard University, Cambridge, MA, 02138, USA.
⁹ Current address: Department of Physics, University of California, Santa Barbara, CA, 93106, USA.
¹⁰ Quantum Theory Project, Depts. of Chemistry and Physics, Univ. of Florida, Gainesville, FL, 32611, USA.

PMID: 29239124
DOI: 10.1002/anie.201709966

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.

Keywords: ab initio calculations; butadiene; conjugation; molecular dynamics; rotational spectroscopy.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.