Toward metal- and catalyst-free Reactions: Deciphering the substituent and external electric field effects on the Diels-Alder reaction between ethylene and nitrosoethylene

The substituents on the diene and/or dienophile can contribute to the decrease or increase of this energy. However, there are other approaches to catalyze chemical reactions, particularly Diels-Alder reactions, for example, the application of an electric field along the reaction axis. The existence of an external electric field (EEF), properly oriented, has the potential to further stabilize or destabilize these electron density contributors and thus influence the energy. The goal of this study was to compare the activation energies of the Diels-Alder reaction between ethylene and nitrosoethylene, using an electric field, Lewis acid (BH3) as catalysts, and the influence of substituents. All calculations were performed with Gaussian09 software. The compounds were fully optimized using the restricted Hartree-Fock method with the basis set 6-31G, and single-point energies were determined with the MP3 method and basis set 6-31G. The effects of EEFs were studied using the “Field = M ± N” keyword with F values (F=±0.125 au and ± 0.080 au) along the preferred axis. The lowest activation barrier is encountered when the electric field is applied, followed by the use of borane as the Lewis acid.