Browsing by Author "Tapia, Ricardo"
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Item Changes in the SNAr reaction mechanism brought about by preferential solvation(Royal Society of Chemistry, 2015) Alarcón-Espósito, Jazmín; Tapia, Ricardo; Contreras, Renato; Campodónico, PaolaWe herein report an experimental and theoretical study on preferential solvation effects for the reactions of 1-fluoro and 1-chloro-2,4-dinitrobenzene towards morpholine in acetonitrile, water and mixtures of them of varying compositions. A detailed kinetic study opens the possibility of analyzing preferential solvation and reaction rates. The kinetic study was complemented with an exploration of the potential energy surface in order to analyze the nature of the molecular interactions. For the fluorine derivative, this analysis reveals that the solvation of the TS in the mode TS1F-water/MeCN clearly outweighs the solvation of TS1F-MeCN/water, thereby suggesting that there is preferential solvation in favor of the aqueous phase.Item How the Nature of an Alpha-Nucleophile Determines a Brønsted Type-Plot and Its Reaction Pathways. An Experimental Study(2022) Campodónico, Paola; Tapia, Ricardo; Suárez, CristianThe reactions between 2-chloro-5-nitro pyrimidine with a serie of α-nucleophile derivatives were kinetically evaluated. The kinetic study was carried out in aqueous media and the data shown an unusual split on the Brønsted type-plot, opening a controversial discussion based on reactivities and possible reaction pathways. These split Brønsted type-plots are discussed over the hypothetical transition state (TS) structures associated to concerted or stepwise mechanisms with emphasis on hydrogen bond interactions between electrophile/nucleophile pair able to determine the reactivities and the plausible reaction routes.Item Mechanism for the SNAr reaction of atrazine with endogenous thiols: experimental and theoretical study(Royal Society of Chemistry, 2017) Calfuman, Karla; Gallardo, Sebastian; Contreras, Renato; Tapia, Ricardo; Campodónico, PaolaReaction mechanism in aromatic nucleophilic substitution reactions is discussed using kinetic study complemented with quantum chemical calculations. The model system is the reaction of a series of biothiols toward atrazine (ATZ) in aqueous media. The proposed reaction mechanism discloses a non-catalyzed pathway and the presence of a deprotonated (thiolate) nucleophile in water suggests that the reaction mechanism is borderline between a stepwise route and a concerted process. The full analysis of the potential energy surface reinforces the addition/elimination mechanism. Despite of numerous attempts to locate transition structures associated with the leaving group departure were unsuccessful, presumably because this step is extremely fast.Item Mechanistic pathways of aromatic nucleophilic substitution in conventional solvents and ionic liquids(Royal Society of Chemistry, 2014) Gazitúa, Marcela; Tapia, Ricardo; Contreras, Renato; Campodónico, PaolaSolvation effects on the reaction mechanism of the title reactions have been kinetically evaluated in 21 conventional solvents and 17 ionic liquids. Solvent polarity affects the catalyzed and non-catalyzed SNAr pathways differently. The ambiphilic character of water and formamide, which act as a hydrogen bond donor/acceptor, induces nucleophilic activation at the nitrogen center of the nucleophile. The ionic liquid EMIMDCN appears to be the best solvent for the SNAr route probably due to the high polarizability of the dicyanamide anion.Item Site activation effects promoted by intramolecular hydrogen bond interactions in SNAr reactions(Royal Society of Chemistry, 2014) Gallardo-Fuentes, Sebastián; Tapia, Ricardo; Campodónico, Paola; Contreras, RenatoThe nucleophilic aromatic substitution reaction of benzohydrazide derivatives towards 2-chloro-5-nitropyrimidine is used as model system to experimentally and theoretically show that intramolecular hydrogen-bond formation operates as a perturbation that elicits a dual response at the reaction center of the transition state (TS) structure, by enhancing the electrophilicity of the pyrimidine moiety and the nucleophilicity of the nitrogen atom of the benzohydrazide fragment. The electronic mechanism can therefore be described as a (non-local) site activation problem.Item Specific nucleophile–electrophile interactions in nucleophilic aromatic substitutions(Royal Society of Chemistry, 2013) Ormazábal-Toledo, Rodrigo; Contreras, Renato; Tapia, Ricardo; Campodónico, PaolaWe herein report results obtained from an integrated experimental and theoretical study on aromatic nucleophilic substitution (S(N)Ar) reactions of a series of amines towards 1-fluoro-2,4-dinitrobenzene in water. Specific nucleophile-electrophile interactions in the title reactions have been kinetically evaluated. The whole series undergoes S(N)Ar reactions where the formation of the Meisenheimer complex is rate determining. Theoretical studies concerning specific interactions are discussed in detail. It is found that H-bonding effects along the intrinsic reaction coordinate profile promote the activation of both the electrophile and the nucleophile. Using these results, it is possible to establish a hierarchy of reactivity that is in agreement with the experimental data. Second order energy perturbation energy analysis highlights the strong interaction between the ortho-nitro group and the acidic hydrogen atom of the amine. The present study strongly suggests that any theoretical analysis must be performed at the activated transition state structure, because the static model developed around the reactant states hides most of the relevant specific interactions that characterize the aromatic substitution process.