A Mechanistic Spectrum of Chemical Reactions

Abstract

The mechanism of chemical reactions between electron donors and acceptors continuously changes with the power of the donors and the acceptors. The interaction between the HOMO (d) of the donors and the LUMO (a*) of the acceptors or delocalization of electrons is important for the reactions. The electron d-to-a* transferred configuration mixes to a significant extent. As the donors and/or the acceptors are strong, their excited configurations appreciably mixes together with the transferred configuration. The d-a and d*-a* orbital interactions are important in addition to the d-a* interaction. Reactions have features characteristic of the excited-state reactions although the donor-acceptor system is not really excited, but in the ground state. This process is termed pseudoexcitation. The a-d-a*-d* interaction is important. For much stronger donors and acceptors, the electron transferred configuration is stable and predominant. Covalent bonds do not form but instead ionic pairs, and electron transfer results. A mechanistic spectrum of chemical reactions is composed of the delocalization, pseudoexcitation, and electron transfer bands.

Violations. How Nature Circumvents the Woodward–Hoffmann Rules and Promotes the Forbidden Conrotatory 4n + 2 Electron Electrocyclization of Prinzbach’s Vinylogous Sesquifulvalene

“…Inagaki, like Epiotis, described the possibility of forbidden [π 2 s + π 2 s ] cycloadditions becoming favored when they involve a donor-substituted alkene reacting with an acceptor-substituted alkene . He described this as “pseudoexcitation”, related to Epiotis’ configuration interaction model.…”

“…Inagaki, like Epiotis, described the possibility of forbidden [π 2 s + π 2 s ] cycloadditions becoming favored when they involve a donor-substituted alkene reacting with an acceptorsubstituted alkene. 42 He described this as "pseudoexcitation", related to Epiotis' configuration interaction model. We note alternatively that alteration of FMO coefficients can reduce the forbiddenness in these cases, although this will also promote stepwise processes via zwitterions.…”