Torsional Energy Barriers in Dimethyl Ether and Perfluoro-Dimethyl Ether: Electronic Structure Contributions

Abstract

The optimized geometries, torsional energy barriers and atomic charge in dimethyl ether and perfluoro-dimethyl ether have been investigated with density functional theory (dft) molecular orbital calculations. The optimized dimethyl ether (DME) and perfluoro-dimethyl ether (PFDME) geometries have been obtained and are in good agreement with experimental results. The torsional energy barriers for both the DME and PFDME have been calculated by incrementally increasing the dihedral angle and performing a full-geometry optimization. The DME and PFDME barriers have been compared, and the geometries of the transition states for both molecules are given. The net atomic charges of both the optimized and transition state species are calculated for both DME and PFDME and shown to be consistent with a stereoelectronic effect (anomeric) that mixes an anti-bonding C–H-centered molecular orbital and an oxygen lone pair. The effects of this antiperiplanar electronic interaction are discussed, and the calculated torsion energy barriers are justified using a simplified second-order bonding model.