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 Title: THE MICROWAVE SPECTRUM AND MOLECULAR STRUCTURE OF (E)-1-CHLORO-1,2-DIFLUOROETHYLENE–ACETYLENE Author(s): Leung, Helen O. Contributor(s): Marshall, Mark D. Subject(s): Mini-symposium: Non-covalent Interactions Abstract: The lowest energy structures for haloethylene-protic acid heterodimers result from an interplay between favorable electrostatic interactions and steric effects. For vinyl fluoride and 1,1-difluoroethylene complexes, steric effects predominate and the resulting planar structure has the acid binding across the double bond (top''), while for trifluoroethylene, favorable electrostatics forces the complexes to adopt a sterically strained, but still planar structure with the acid at one end of the olefin (side''). Substitution of a fluorine atom with chlorine allows a relaxation of steric requirements and the side binding motif to chlorine is observed in ({\it Z})-1-chloro-2-fluoroethylene–acetylene despite the presence of the more electronegative fluorine atom. Similarly, in 2-chloro-1,1-difluoroethylene ethylene–acetylene, the acetylene prefers to adopt side binding to chlorine despite having the option of top binding to fluorine. In ({\it E})-1-chloro-1,2-difluoroethylene, the possibilities are switched to top binding to chlorine and side binding to fluorine. Although the side binding arrangement to fluorine is predicted to be lower in energy than top binding to chlorine, a non-planar, crossed geometry, with the centers of the HCCH triple bond and ethylene double bond approximately aligned with each other is predicted as the global minimum when not correcting for basis set superposition error. When the correction is made, the non-planar geometry has an energy higher than both side and top binding. The microwave spectra of four isotopologues of the ({\it E})-1-chloro-1,2-difluoroethylene-HCCH complex reveal that the side binding structure is indeed the one with the lowest energy. This structure is discussed in terms of the balance between electrostatics and sterics. Issue Date: 2019-06-18 Publisher: International Symposium on Molecular Spectroscopy Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/104299 DOI: 10.15278/isms.2019.TB02 Rights Information: Copyright 2019 Helen O. Leung Date Available in IDEALS: 2019-07-152020-01-25
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