A Theoretical Study of the Stevens Rearrangement of Methylammonium Methylide and Methylammonium Formylmethylide

Abstract

Ab initio and semi-empirical molecular orbital theory has been used to study the reaction pathways of the Stevens rearrangement of the prototype methylammonium methylide and methylammonium formylmethylide . For both reactions, the stepwise (free radical) process is predicted to require less energy than the concerted rearrangement (in accordance with experimental suggestions). With inclusion of electron correlation, the energy difference between these pathways is reduced; however, for the smaller system at the CCSD/6-31G(d) level of theory, the free radical process is still favoured by over 180 kJ mol^-1. For both systems, the concerted transition structures for the pericyclic mechanisms reveal that some amount of bonding is retained in these formally symmetry-forbidden processes.