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Published on: August 13, 2020
Molecular Structure, Equilibrium Conformation, and Ring-Puckering Motion in 1,1,3,3-Tetramethylcyclobutane. An
Jason W Sandwisch1, Lise Hedberg1, Kenneth Hedberg1
1Department of Chemistry, Oregon State University , Corvallis, Oregon 97331-4003, United States.
Abstract:
The molecule cyclobutane (CB) has a nonplanar carbon skeleton folded around a line connecting diagonally opposite atoms. The puckering angle (the change from planarity) of ∼30° is generally attributed to steric repulsion between the four sets of adjacent methylene groups that would be opposed in a planar ring and is relieved by the puckering. According to this criterion, a similar molecule, 1,1,3,3-tetramethylcyclobutene (TMCB), in which adjacent methylene groups do not exist, would be expected to have a planar ring in the equilibrium form. We have investigated the structure of TMCB to test this expectation. Two models were designed for the tests: one having D2h symmetry (planar ring) and one of C2v symmetry (nonplanar ring). Each model incorporated the dynamics of large-amplitude bending around a line joining the methylene groups. Our results suggest the D2h model is to be preferred. Dynamic averages (rg/Å; ∠g/deg) of the more important distances and angles in the D2h model with estimated 2σ uncertainties, are as follows.
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