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Interaction Mechanisms Between Biochar and Herbicides
Published in Kassio Ferreira Mendes, Interactions of Biochar and Herbicides in the Environment, 2022
Rodrigo Nogueira de Sousa, Matheus Bortolanza Soares, Felipe Hipólito dos Santos, Camille Nunes Leite, Kassio Ferreira Mendes
Whereas nucleophilic substitution is a chemical reaction in which the nucleophile replaces a functional group of another electron-deficient molecule (Carey and Sundberg 2007). Possibly, in biochar, the main nucleophilic substitution occurs in an aromatic ring, also known as aromatic nucleophilic substitution. Nucleophilic aromatic substitution occurs through the addition of a nucleophile to the aromatic ring followed by the loss of a functional group (Kalsi 2000).
Hydrolysis
Published in Richard A. Larson, Eric J. Weber, Reaction Mechanisms in Environmental Organic Chemistry, 2018
Richard A. Larson, Eric J. Weber
Hydrolysis is an example of a larger class of reactions referred to as nucleophilic displacement reactions in which a nucleophile (an electron-rich species containing an unshared pair of electrons) attacks an electrophilic atom (an electron-deficient reaction center). Hydrolytic processes encompass several types of reaction mechanisms that can be defined by the type of reaction center (i.e., the atom bearing the leaving group, X) where hydrolysis occurs. The reaction mechanisms encountered most often are direct and indirect nucleophilic substitution and nucleophilic addition-elimination.
Reaction probability and defluorination mechanisms of a potent greenhouse gas SF5CF3 attacked by CH3 radical: a theoretical study
Published in Molecular Physics, 2018
Yan Liu, Yue-tian Huang, Wen-liang Wang
The type of inserting and breaking mechanism will undergo complex muti-channel processes to decompose three HF molecules successively and produce an alkyne derivative, as shown in Figure 3(b). It is found that there are three entrance paths to form product Dp10 (SF5 + CH3CF3) via TS14 and TS15 (two different mechanisms) or Dp11 (CH3SF5 + CF3) via TS16 firstly. In TS14, the CH3 radical attacked and extracted the –CF3 group directly from the back side of CF3SF5 molecule, as shown in Figure 1. The process would result in the breaking of the old C–S bond and the forming of a new C–C bond, which is defined as the mechanism of bimolecular nucleophilic substitution (SN2 mechanism). But the SN2 mechanism has a higher energy barrier of 335.7 kJ mol−1. Another path to form Dp10 will go through the transition state TS15 with the energy barrier of 301.3 kJ mol−1, which is 34.4 kJ mol−1 lower than that of TS14. In TS15, the CH3 radical would insert in the C–S bond of CF3SF5 and also lead to the breaking of C–S bond to decompose a SF5 molecule. Meanwhile, CH3 and CF3 groups will combine together to form CH3CF3 molecule. Alternatively, the CH3 radical could combine –SF5 group and decompose the –CF3 group to form the product Dp11 via the transition state TS16 with the barrier of 332.4 kJ mol−1. It is noted that the products Dp10 and Dp11 could convert to each other via TS17 by through the –CH3 group swinging between –CF3 and –SF5 groups. The barrier from Dp10 to Dp11 is 414.7 kJ mol−1 and that of reverse reaction is 275.7 kJ mol−1. The decomposing products CH3SF5 and CF3 would eliminate a HF molecule and form intermediate IM1 via TS18 with an energy barrier of 383.9 kJ mol−1. In IM1, one of H atom could shift from the inside C atom to the end and form IM2 via TS19 with barrier of 140.7 kJ mol−1. IM2 would then dissociate a HF molecule in the –CF2H group to produce IM3 with a moderate barrier of 218.7 kJ mol−1. Competing to the two-step reactions, IM1 also could break its C–F and C–H bonds directly to produce IM3 + HF via TS21 with a slightly higher barrier of 222.1 kJ mol−1.