Steric and Electronic Effects on the Mechanism of the Stevens Rearrangement—Large Organic Ylides of Unusually High Symmetry

Ab initio molecular orbital theory has been used to study the Stevens rearrangement of trimethylammonium methylide, dimethylammonium formylmethylide and trimethylammonium formylmethylide . For each system, the rearrangement is predicted to proceed via dissociation to two radical species followed by recombination to the appropriate alkylamine . In no case is the concerted pathway competitive. Steric effects are less important than electronic effects in stabilizing the ylides, and the introduction of a carbonyl group lowers the energy barrier towards the ylides is predicted to have rigorous C8 symmetry; this unusual situation is brought about by the nature of the substituents around the positive nitrogen and the planarity of the remaining negative portion of the molecule.