Advanced oxidation processes (AOPs) are based on the in situ production of hydroxyl radicals (•OH) and reactive oxygen species (ROS) in water upon irradiation of the sample by UV light, ultrasound, electromagnetic radiation, and/or the addition of ozone or a semiconductor. Diclofenac (DCF), one of the emerging organic contaminants (EOC), is of environmental concern due to its abundancy in water and is known to be subjected to AOPs. The current study uses density functional theory (DFT) to elucidate the mechanisms of the reactions between •OH and DCF leading to degradation by-products, P1-P9. The initial encounter of DCF with •OH is proposed to lead to either the abstraction of a hydrogen or the addition of the hydroxyl radical to the molecule. The results showed that OH addition radicals (R ) are both kinetically and thermodynamically favored over H abstraction radicals (R). The intermediate radicals give degradation by-products by subsequent reactions. The by-products P7 and P8 are easily formed in agreement with experimental findings. Finally, acute toxicities at three trophic levels are estimated with the Ecological Structure Activity Relationships program. DCF and most of the by-products were found to be harmful to aquatic organisms, P9 being the only by-product that is not harmful at all three trophic levels.
The reactions between low-valent Rh(I) and Ir(I) metal–carbonyl complexes and arylnitrile oxides possess the electronic and structural features of 1,3-dipolar cycloadditions. Density functional theory (DFT) calculations on these reactions, involving both cyclopentadienyl and carboranyl ligands on the metal carbonyl, explain the ease of the chemical processes and the stabilities of the resulting metallaisoxazolin-5-ones. The metal–carbonyl bond has partial double bond character according to the Wiberg index calculated through NBO analysis, and so the reaction can be considered a normal 1,3-dipolar cycloaddition involving M═C bonds. The rates of formation of the metallacycloadducts are controlled by distortion energy, analogous to their organic counterparts. The superior ability of anionic Ir complexes to share their electron density and accommodate higher oxidation states explains their calculated higher reactivity toward cycloaddition, as compared to Rh analogues.
A DFT study is carried out in order to elucidate the racemization and cyclization mechanism as well as the atroposelectivity during the synthesis of 2-thiohydantoins. Computational data shows that the racemization occurs after cyclization with the assistance of triethyl amine.
In this study the exo selectivity in the hetero Diels-Alder reaction of atropisomeric 5-benzylidine-2-arylimino-3-aryl-thiazolidine-4-thiones with norbornene was investigated with computational tools. Taking into account the M/P chiral character of the o-methoxyphenyl substituted heterodienes in addition to the exo/endo selectivity, 8 different transition structures were located. Based on the direction of approach of the diene and the dienophile for each plausible path it is found that endo products are not preferred because of the large distortion of norbornene and the rather eclipsed conformations of these transition state structures. Computational results are consistent with the experimental exo/endo selectivity. The computational methodology (M06-2X/6-31+G(d)//B3LYP/6-31+G(d)) was justified by comparison of the experimental rotational barriers with the calculated ones for selected compounds.
In this study, the rate of photopolymerization (Rp) of 21 alkyl methacrylates is correlated with the chemical properties of their monomeric radicals by making use of the enthalpic and polar effects of these radicals. Based on these properties, a general non‐linear expression is derived by optimizing the radicals and evaluating both their stability and polar effects, via the radical electrophilicity, using density functional theory. The expression performs quite well in predicting Rp for 16 of the 21 methacrylates with an R2 value of 0.9384, but does not hold for too unstable and/or too nucleophilic radicals. Increasing the stability or decreasing the nucleophilicity of the monomeric radical results in a higher polymerization rate; in addition, the influence of the polar effects becomes larger for more stable radicals. Methacrylates containing a pendant phenyl, where π–π stacking plays an important role, are experimentally found to have a higher polymerization rate than predicted.
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