A COMPUTATIONAL INVESTIGATION OF THE MOLECULAR-GEOMETRY AND ROTATIONAL BARRIERS IN ETHYL METHYL-ETHER

Ab initio (HF/6-31G(d) and MP2/6-31G(d)) and semiempirical (AMI and PM3) molecular orbital methods were used to investigate the two equilibrium and the two transition-state conformations on the rotational potential surface of ethyl methyl ether. All levels of theory gave geometries and frequencies in accordance with experimental values. Ab initio relative energies DELTAH0 agreed with experiment to within about 0.4 kcal mol-1, except for the gauche-gauche isomerization barrier, for which the error is about 3 kcal mol-1. There is little improvement at the MP2/6-311 + G(3df,2p) level of theory. Semiempirical DELTAH0 values are no more accurate overall, but show more systematic deviations from experiment, which arise from an underestimation of the stability of the trans conformer.