# QTAIM Based Computational Assessment of Cleavage Prone Bonds in Highly Hazardous Pesticides

## TL;DR

This paper uses computational methods to identify weak bonds in dangerous pesticides that are likely to break during degradation.

## Contribution

The study introduces an integrated framework combining QTAIM, conceptual DFT, and TAFF to identify and validate cleavage-prone bonds in pesticides.

## Key findings

- QTAIM identifies weak bonds like P–O, P–S, and P–N linkages in organophosphate pesticides.
- Conceptual DFT shows global and local reactivity descriptors are more sensitive to solvation than QTAIM parameters.
- TAFF analysis confirms QTAIM-identified bonds as the most reactive sites for degradation.

## Abstract

Highly Hazardous Pesticides (HHPs) pose severe risks to human health and the environment, making it essential to understand their molecular stability and degradation pathways. In this study, the Quantum Theory of Atoms in Molecules (QTAIM) was applied to four representative organophosphate pesticides, allowing the identification of electronically weak bonds as intrinsic sites of lability. These findings are consistent with reported hydrolytic, oxidative, enzymatic, and microbial degradation routes. Importantly, QTAIM descriptors proved largely insensitive to solvation, confirming their intrinsic character within the molecular electronic structure. To complement QTAIM, conceptual DFT (Density Functional Theory) reactivity indices were analyzed, revealing that solvent effects induce more noticeable variations in global and local descriptors than in topological parameters. In addition, a Topological Analysis of the Fukui Function (TAFF) was performed, which mapped nucleophilic, electrophilic, and radical susceptibilities directly onto QTAIM basins. The TAFF analysis confirmed that bonds identified as weak by QTAIM (notably P–O, P–S, and P–N linkages) also coincide with the most reactive sites, thereby reinforcing their mechanistic role in degradation pathways. This integrated framework highlights the robustness of QTAIM, the sensitivity of global and local reactivity descriptors to solvation revealed by conceptual DFT, and the complementary insights provided by TAFF, contributing to risk assessment, remediation strategies, and the rational design of safer pesticides.