ALBERT

Description: The paper represents an attempt to provide a sound theoretical subsidy for the so-called “curved arrow formalism,” which proved unprecedented usefulness in shaping our ideas about the mechanisms of organic reactions. The basic idea is to characterize the extent to which the electron pairs are conserved or broken for a given nuclear configuration by the probability of finding the pair of electrons of opposite spin in a given point of space. This probability is quantitatively given by the αβ component of the pair density, with coinciding positions of both electrons. As a function of 3 variables, the quantity Π αβ (r, r) can be displayed in 3D and the monitoring of the snapshots of this quantity for different points along the reaction path thus can bring new interesting insights into the details of bond reorganization in the course of reactions. The paper reports the application of the above approach for the detailed scrutiny of the differences in the electron reorganization of allowed and forbidden pericyclic reactions at the level of simple topological description in terms of overlap determinant method. Despite its simplicity, the approach provided new interesting insights into the factors underlying the different role of electron pairs in allowed and forbidden pericyclic reactions, and we believe that this simple approach could inspire further straightforward extensions that would allow to apply its formalism at the level of contemporary sophisticated computations to real systems of chemical interest. The proposed approach relies on the idea to characterize the extent to which the electron pairs are conserved or broken by the probability of finding the pair of electrons of opposite spin at a given point of space. This probability is given by the αβ component of the pair density Π αβ ( r ,  r ) , and monitoring of this quantity in the form of snapshots for different points along the reaction path brings new insights into the destiny of electron pairs in chemical reactions.