New Insight into the Chloroacetanilide Herbicide Degradation Mechanism through a Nucleophilic Attack of Hydrogen Sulfide

Abstract

The nucleophilic attack of hydrogen sulfide (HS−) on six different chloroacetanilide herbicides was evaluated theoretically using the dispersion-corrected hybrid functional wB97XD and the 6-311++G(2d,2p) Pople basis sets. The six evaluated substrates were propachlor (A), alachlor (B), metolachlor (C), tioacetanilide (D), β-anilide (E), and methylene (F). Three possible mechanisms were considered: (a) bimolecular nucleophilic substitution (SN2) reaction mechanism, (b) oxygen assistance, and (c) nitrogen assistance. Mechanisms based on O- and N-assistance were discarded due to a very high activation barrier in comparison with the corresponding SN2 mechanism, with the exception of compound F. The N-assistance mechanism for compound F had a free activation energy of 23.52 kcal/mol, which was close to the value for the corresponding SN2 mechanism (23.94 kcal/mol), as these two mechanisms could occur in parallel reactions with almost 50% of each one. In compounds A to D, an important electron-withdrawing effect of the C=O and C=S groups was seen, and consequently, the activation free energies in these SN2 reactions were smaller, with a value of approximately 18 kcal/mol. Instead, compounds E and F, which have a CH2 group in the β-position, presented a higher activation free energy (≈22 kcal/mol). Good agreement was found between experimental and theoretical values for all cases, and a reaction force analysis was performed on the intrinsic reaction coordinate profile in order to gain more details about the reaction mechanism. Finally, from the natural bond orbital (NBO) analysis, it was possible to evaluate the electronic reorganization through the reaction pathway where all the transition states were early in nature in the reaction coordinate (δBav < 50%); the transition states corresponding to compounds A to D turned out to be more synchronous than those for compounds E and F.

Sulfonylation of Five‐Membered Aromatic Heterocycles Compounds through Nucleophilic Aromatic Substitution: Concerted or Stepwise Mechanism?

“…Interestingly, we found different results for reaction C mechanism, depending on the calculation method used. The reaction appears to follow a concerted mechanism when the Becker three‐parameters Lee‐Yang‐Parr, B3LYP−D3, functional is used while the stepwise mechanism is found with the ωB97XD functional . Therefore, to further investigate this reaction and determine which of these methods is more adequate for the description of this reaction, ab initio calculations at the second order Møller‐Plesset perturbation theory, MP2, were performed.…”

A computational study of the reaction mechanism involved in the fast cleavage of an unconstrained amide bond assisted by an amine intramolecular nucleophilic attack

“…25 It is important to point out that, ωB97XD in conjunction with the split-valence 6-311 + g(d,p) Pople's basis set has been broadly used to computationally study organic reaction mechanisms. [26][27][28][29][30][31] Solvent effects were included in all the calculations using the solvation model density (SMD) protocol. 32,33 For mechanisms 1-6, geometry optimizations, and frequency calculations of the reactants (R), INT, products (P), and TS were performed.…”

Theoretical Study of the Adsorption Process of Antimalarial Drugs into Acrylamide-Base Hydrogel Model Using DFT Methods: The First Approach to the Rational Design of a Controlled Drug Delivery System

“…The minimum potential energy surface of three antimalarial drugs and their complexes with polyacrylamide models (DAA, TAA, DAA-CQ, DAA-PQ, DAA-AQ, TAA-CQ, TAA-PQ and TAA-AQ) were performed at Density Functional Theory (DFT) level, using functional exchange-correlation of wb97xd, taking into account both short-range and long-range interactions, combined with the basic set 6-31++G(d,p), from Gaussian 16 software [41]. This methodology has demonstrated to be accurate enough to evaluate the interaction between organic molecules [42][43][44].…”