Ab initio molecular orbital studies on C2H5O+ and C2H4FO+: oxonium ion, carbocation, protonated aldehyde, and related transition-state structures

Abstract

We have investigated the effect of including electron correlation in calculations of the geometries and energies of the oxonium ion, carbocation, and protonated aldehyde species of oxirane and monofluorooxirane by comparing data obtained at the RHF/6-31G * //RHF/6-31G * , MP2/6-31G * //RHF/6-31G * , and MP2/6-31G * //MP2/6-31G * levels. As well as characterizing the oxonium ions and carbocations as stable intermediates or as transition states, many of the transition states interlinking the stable intermediates have also been identified. The inclusion of electron correlation in the energy calculations is found to favor the ring structures, whereas its inclusion in the geometry optimization scarcely alters the reaction energies and activation energies