Optimized structures and proton affinities of fluorinated dimethyl ethers: an ab initio study

Abstract

Ab initio methods have been used to investigate the proton affinity and the geometry changes upon protonation for the molecules (CH 3) 2O, (CH 2F) 2O, (CHF 2) 2O, and (CF 3) 2O. Geometry optimizations were performed at the MP2/3-21G level, and the resulting geometries were used for single-point energy MP2/6-31G ∗∗ calculations. The proton affinity calculated for (CH 3) 2O was 7 kJ mol −1 from the experimental value, within the desired variance of ±8 kJ mol −1 for G2 theory, suggesting that the methodology used in this study is adequate for energy difference considerations. For (CF 3) 2O, the calculated proton affinity of 602 kJ mol −1 suggests that perfluorinated ether molecules do not act as Lewis bases under normal circumstances, e.g. degradation of commercial lubricants in tribological applications.