Quantum Chemical Molecular Models for Fluorinated Polymers: Visualization of Structures and Vibrational Motions

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Abstract
Ab initio molecular orbital theory has been used to cal culate the electronic structure of model perfluoroalkanes, perfluoroethers, and a fluorinated macrocycle that binds fluoride ion. The molecular geometries were optimized. The perfluoroalkanes and the perfluoroethers do not have all trans configurations but rather show twisting of 10° to 20° about the C-C and C-O bonds. The molec ular force fields were calculated in the harmonic ap proximation. The low-frequency normal modes are dis played in the accompanying video. These low-energy modes involve coupled torsions. The visualization shows the various couplings of the torsional degrees of freedom. Certain features including the presence of "spectator" methyl side groups and of only a small cou pling of C-O torsions to the C-C bonds in the chain were revealed. Other features of the visualization allow one to study sterically accessible sites that are potentially reactive in these systems.