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4690037 
Journal Article 
The Molecular Structure of gauche-1,3-Butadiene: Experimental Establishment of Non-planarity 
Baraban, JH; Martin-Drumel, MA; Changala, PB; Eibenberger, S; Nava, M; Patterson, D; Stanton, JF; Ellison, GB; Mccarthy, MC 
2018 
Yes 
Angewandte Chemie (International Edition)
ISSN: 1433-7851
EISSN: 1521-3773 
57 
7 
1821-1825 
English 
29239124 
WOS:000424212300010 
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. 
Chemistry; ab initio calculations; butadiene; conjugation; molecular dynamics; rotational spectroscopy; Dihedral angle; 1,3-Butadiene; Molecular structure; Chemical bonds