Theoretical studies of the mechanism of the Wittig olefination reaction

The results we have obtained indicate that the common procedure of utilizing of the mythical Wittig half-reaction to theoretically describe the mechanism of the Wittig olefination reaction does not give consistent results when electron correlation is taken into account in the model hamiltonian. We propose that the reaction of Me3P=CH2 with formaldehyde is the smallest system that can be used to properly model the Wittig olefination reaction. The best compromise between accuracy and computational expense is to compute the molecular geometries with the HF/6-31G* methodology and the energy at the MP2/6-31G*/HF-6-31G* level. We applied the methodology that we have developed to the study of reaction of a series of stabilized, semistabilized and unstabilized ylides with acetaldehyde.