TITLE:
An Adjusted Model for Simple 1,2-Dyotropic Reactions. Ab Initio MO and VB Considerations
AUTHORS:
Henk M. Buck
KEYWORDS:
Type-I Dyotropic Reactions; MO Calculations; Van ’t Hoff Model Considerations; Halogen and Methyl Exchange; Conflicting Models
JOURNAL NAME:
Open Journal of Physical Chemistry,
Vol.3 No.3,
August
6,
2013
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 aδor 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 SN2 reactions each containing four
electrons. The van ’t Hoff dynamics appears a useful model in order to illustrate the
computations in a straightforward manner.