The reaction fragility spectrum

Abstract

We report an original method that provides a new insight into the reaction mechanism by direct observation of bond breaking and formation. Variations of the diagonal elements of the Hessian along the IRC are shown to reflect the anharmonic properties of the system that are induced by electron density modifications upon the reaction. This information is presented in the form of the reaction spectrum, demonstrating how particular atoms engage in the reorganization of bonds. The test reactions are: HCOF synthesis and HONS isomerization.

Evolution of the atomic valence observed by the reaction fragility spectra on the reaction path

“…It describes the change of the force constant (the divergence) of the link of an atom (cumulative force constant) along the reaction path. The term fragility, used in other branches of chemistry, has been proposed for this quantity [6]. By the conceptual DFT analysis, an important albeit approximate conclusion has been arrived at: the electron density change around an atom in question is reflected by the atomic fragility a A ξ (Eqs.…”

“…We have developed regional chemical potential evolution and identified the most reactive state along the IRC reaction path [4]. Recently, we introduced a new concept of reaction fragility to identify reaction mechanism and to spot electron density modifications along the IRC reaction path [5,6] . We introduced a novel approach, aiming at observation of the electron density flow between atoms, rather than tracing the global parameters of the system.…”

Intramolecular proton transfer in the isomerization of hydroxyacetone: Characterization based on reaction force analysis and the bond fragility spectrum

“…Recent work has utilized these properties in order to track the modification of electron densities around atoms and bonds respectively throughout a chemical reaction. [74,77] It has been proven that the changes to the H-F force derivative throughout a chemical reaction should primarily be attributable to the modulation in electron density in the internuclear region between atoms A and B. [105] This derivative throughout the reaction coordinate is termed the "bond fragility spectrum" (a AB ξ ), if a connectivity matrix is calculated for every point along the reaction coordinate the bond fragility spectrum can be calculated as:…”

“…[72,73] Additionally, a recent method developed by Piotr Ordon and coworkers called the bond fragility spectrum aims to analyze the sequence of bond breaking/formation for a reaction by investigating the derivative of properties based on the molecular Hessian. [74][75][76][77] In the present study, we utilize all of these theoretical tools in order to characterize the proton transfer reactions involved in the isomerization of hydroxyacetone to 2-hydroxypropanal. Specifically we will characterize the nature of each elementary reaction step as SPT or DPT, and for all DPT mechanisms we will classify their relative synchronicity.…”

The Connectivity Matrix: A Toolbox for Monitoring Bonded Atoms and Bonds

“…Persuasive pictures for bond formating/breaking along IRC have already been demonstrated for several reactions as the reaction fragility (RF) spectra for atoms and bonds. 39,40,43,44 The aim of this work is to review briefly the properties of the divergences (eq 2) collected in the connectivity matrix for a system, in order to demonstrate their new explicit relation to the electron density function (section 2). Application of the concept to tentative separation of the potential energy of a system into atomic contributions and their observation in a system undergoing a reaction has been presented in sections 3 and 4.…”