Revisiting the Bonding Evolution Theory: A Fresh Perspective on the Ammonia Pyramidal Inversion and Bond Dissociations in Ethane and Borazane

This work offers a comprehensive and fresh perspective on the bonding evolution theory (BET) framework, originally proposed by Silvi and collaborators [J. Phys. Chem. A, 1997, 101, 7277–7282]. By underscoring Thom’s foundational work, we identify the parametric function characterizing bonding events along a reaction pathway through a three-step sequence to establish such association rigorously, namely: (a) computing the determinant of the Hessian matrix at all potentially degenerate critical points, (b) computing the relative distance between these points, and (c) assigning the unfolding based on these computations and considering the maximum number of critical points for each unfolding. In-depth examination of the ammonia inversion and the dissociation of ethane and ammonia borane molecules yields a striking discovery: no elliptic umbilic flag is detected along the reactive coordinate for any of the systems, contradicting previous reports. Our findings indicate that the core mechanisms of these chemical reactions can be understood using only two folds, the simplest polynomial of Thom\u27s theory, leading to considerable simplification. In contrast to previous reports, no signatures of the elliptic umbilic unfolding were detected in any of the systems examined. This finding dramatically simplifies the topological rationalization of electron rearrangements within the BET framework, opening new approaches for investigating complex reactions

Are There Only Fold Catastrophes in the Diels–Alder Reaction Between Ethylene and 1,3–Butadiene?

This work revisits the topological characterization of the Diels–Alder reaction between 1,3–butadiene and ethylene. In contrast to the currently accepted rationalization, we here provide strong evidence in support of a representation in terms of seven structural stability domains separated by a sequence of 10 elementary catastrophes, but all only of the fold type, i.e., C4H6 + C2H4 : 1–7– [FF]F[F†F†][F†F†][FF]F†–0 : C6H10. Such an unexpected finding provides fundamental new insights opening simplifying perspectives concerning the rationalization of the CC bond formation in pericyclic reactions in terms of the simplest Thom’s elementary catastrophe, namely the one–(state) variable, one–(control) parameter function

On the Nature of Bonding in the Photochemical Addition of Two Ethylenes: C-C Bond Formation in the Excited State?

In this work, the 2s+2s (face-to-face) prototypical example of a photochemical reaction has been re-examined to characterize the evolution of chemical bonding. The analysis of the electron localization function (as an indirect measure of the Pauli principle) along the minimum energy path provides strong evidence in support that CC bond formation occurs not in the excited state but at the ground electronic state after crossing the rhombohedral S1/S0 conical intersection. <br /

Average local ionization potential within the framework of the electron localization function

958-964In this work we explore new insights arising from simple indices intended to measure the average local vertical ionization energy associated to ELF valence population basins. The model has been computationally tested on simple isothiocyanate compounds (R-N=C=S) revealing that the proposed relationships correctly establish both the inductive and electronegativity effects of electronegative groups along the examined series, i.e., methyl- < germyl- < hydrogen- < acetyl- < chlorodifluoroacetyl-, in agreement with the available experimental observations. The proposed energetical descriptors are expected to contribute to the search of relationships between the spatial topology of electronic populations and energetical aspects of the bonding. The present results enhance the possibility of gaining insight into chemical bonding and reactivity within the ELF topological-defined framework of chemical rationalization