An Adjusted Model for Simple 1,2-Dyotropic Reactions. <i>Ab Initio</i> MO and VB Considerations

Abstract

With an adjusted model, we reconsider simple 1,2-dyotropic reactions with the introduction of a concept based on the intramolecular dynamics of a tetrahedron (van 't Hoff modeling). In fact the dyotropic reactions are strongly related to conversions originated from neighbouring group participation or anchimeric assistance, defined as the interaction of a center with a lone pair of electrons in an atom and the electrons present in a ϭ or π bond. The researchful 1,2-dyotropic reactions, based on the 1,2-interchange of halogens, methyl and hydrogen taking place in a concerted fashion, are in competition with the two-step reaction in which the neighbouring group participation or anchimeric assistance comes to full expression by ionic dissociation of the other exchangeable (halogen) atom. As to be expected there is an essential difference between halogen or methyl exchange regarding the number of electrons participating in the transition state. This aspect becomes evident in the geometries of the corresponding transition state geometries. In this paper we refer to ab initio MO calculations and VB considerations. We consider the 1,2-halogen exchange as a combination of two S N 2 reactions each containing four electrons. The van 't Hoff dynamics appears a useful model in order to illustrate the computations in a straightforward manner.

Three-Center Configuration with Four,Three, and Two Electrons for Carbon,Boron, Hydrogen, and Halogen Exchange. A Model and Theoretical Study with Experimental Evidence

“…At the end halogen transfer reactions in a three-center bonding are considered because they are closely related to the variety of elementary particles in basic organic chemistry. A short introduction with relevant bond lengths is given in Figure 1, summarizing the aforementioned results for linear three-center four-, three-, and two-electron systems at the MP2/6-31 + G(d,p) level of theory [1] in combination with the model findings between parentheses [2]- [6]. The substituents are tert-butyl groups, and X represents H − , H • , H + , 3 CH + , and F − .…”