Theoretical investigation of the thermochemistry of hydrofluoroethers

The enthalpies of formation and the C–H bond strengths of fluorinated dimethylethers were derived at 298.15 K by ab-initio calculations at the MP2/3-21++G(2d,2p), MP2/6-31++G(2d,2p) and MP2/6-311++G(2d,2p) levels of theory, and are compared with the results of recent calculations by the G2(MP2) method. Theoretical calculations were also performed for the corresponding fluorinated ethanes in order to compare the results with those derived by the BAC–MP4 method and with the available experimental data. The calculations at the MP2/6-31++G(2d,2p) level are considered more reliable on the basis of the closer agreement between theory and experiment. The results suggest that the introduction of the ether linkage –O– leads to lower C–H bond strengths only in mildly F-substituted dimethylethers. Heavily F-substituted dimethylethers possess stronger C–H bonds than their fluoroethane counterparts and therefore their tropospheric reactivity is expected to be lower.