ABINITIO MOLECULAR-ORBITAL CALCULATIONS OF CONFORMATIONAL ENERGIES OF ETHYL METHYL-ETHER - BASIS SET AND ELECTRON CORRELATION-EFFECTS

The geometries and energies of the two minima and the two transition states on the rotational potential surface of ethyl methyl ether have been calculated by the ab initio molecular orbital method. The effect of the basis set on the calculated conformational energies was investigated by performing single-point computations with several basis sets [up to 6-311G(2d,2p)]. The electron correlation effect was included by Moller-Plesset perturbation calculations. Vibrational frequencies and zero-point and thermal vibrational energies were calculated. Relative energies calculated at the MP2/6-311G(2d,2p)//HF/6-31G* level were 0.0, 1.33, 2.52 and 6.41 kcal mol-1, respectively. These values were different from the previously reported values obtained at the HF level using minimal or double-zeta type basis sets.