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On the Unusual Synclinal Conformations of Hexafluorobutadiene and Structurally Similar Molecules
An explanation is
presented for the unusual conformations of some
molecules that contain the Cī»CāCī»C core, namely,
butadienes, biphenyls, and styrenes. Small substituents often induce
a synclinal conformation, which brings the substituents into close
proximity, and sometimes, there is no anticlinal minimum at all. This
would not be predicted from steric repulsion arguments nor would it
be expected that atoms that are nonbonded in a Lewis structure would
approach closer than the sum of their van der Waals radii. Atomic
energies calculated according to the quantum theory of atoms in molecules
(QTAIM) do not show a consistent pattern for these structurally similar
molecules, nor are intersubstituent bond paths consistently found,
nor favorable diatomic interaction energies calculated using the interacting
quantum atoms (IQA) scheme. Instead, the synclinal conformations are
found to be driven by the attraction energy of the electron distribution
of the carbon atoms and the nuclei of the molecule