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Alkyl Halides and Substitution Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
A leaving group is the group that “leaves” in a substitution reaction. Actually, the leaving group (Br in the preceding question) does not spontaneously leave but is “kicked out” (displaced) by the nucleophile as the nucleophile collides with the electrophilic carbon in this substitution reaction. What is a reactive intermediate?
Synthesis and characterization of the Co(II) and Ni(II) complexes of 1,3,4-thiadiazole-derived ketones and secondary alcohols: thermal and magnetic properties
Published in Journal of Coordination Chemistry, 2021
Melih Erdogan, Kubra Kiymaz, Hakan Tahtaci, Saban Uysal
In the second step of the study, N-(5-((2-(3,4-dichlorophenyl)-2-oxoethyl)thio)-1,3,4-tiadiazole-2-yl)benzamide derivatives (5a-j) were synthesized by reaction of 3 with various benzoyl chloride derivatives (4a-j) in the presence of pyridine with yields varying between 65% and 84%. These reactions are typical nucleophilic acyl substitution reactions that occur through nucleophilic addition and elimination to the carbonyl carbon. Acyl groups produce substitution reactions, as expected. Chlorine that has bonded to the carbonyl carbon can be removed by protonation if necessary. Acyl chlorides usually react by losing the chloride ion, a very good leaving group. The lone electron pair on the amino group in 3 attacks the carbonyl carbon of the acyl derivatives (4a-j) as a nucleophile. A proton from the amino group transfers to chloride and the electron pair on oxygen attacks the carbon to form a double bond, with hydrogen chloride turning into pyridinium chloride salt. After the reaction is completed, when the raw materials formed are washed with a large amount of water, pyridinium chloride is removed from the medium. The proposed reaction mechanism for formation of 5a-j is given in Figure 2.
Phosphoester hydrolysis promoted by quinoline functionalized Ni(II) and Zn(II) complexes
Published in Journal of Coordination Chemistry, 2021
Qazi Mohammad Junaid, Popuri Sureshbabu, Shahulhameed Sabiah
During the last decade, there has been considerable interest in elucidating the role of metal ions in the hydrolysis of phosphates [3]. Transition metal complexes, lanthanide complexes and actinides have all been utilized as catalysts for the hydrolysis of DNA and model phosphodiesters [4–19]. Metal ions coordinated to organic frameworks like pyridyl- and quinoline derivatives offer the advantage of a more easy examination of the substrate structure-activity relationship (SSAR) and the role of the metal ion. The metal ion has been suggested to play roles of: (1) Lewis acid activation of the substrate, (2) creation of a nucleophile and (3) generation of a good leaving group of the substrate [20]. In recent years, a broad range of mononuclear metal-based artificial nucleases were synthesized by optimizing ligand design [21–25]. By careful ligand designing, reaction rates and turnovers can be improved.
Theoretical study on chemical fixation of carbon dioxide with aziridine into cyclic carbamate catalysed by purine/HI system
Published in Molecular Physics, 2021
Teshome Mender Gezhagn, Abdudin Geremu Temam, Teshome Abute Lelisho
Selected geometric parameters of the species involved in cyclisation step of mechanism II are summarised in Table 8. It has contribution to validate the optimised TS2(M–N). The cleavage of I14–C16 bond and formation of C16–O25 bond were confirmed by elongation of I14–C16 bond from 2.40 Å to 3.69 Å and decreasing of C16–O25 bond from 3.33 Å to 1.65 Å, respectively. The leaving group I− ion is detached from the product cyclic carbamate and the catalyst was recovered, as shown in Figure 9. As given in Table 8, the decrease in distance between C24 and N22 from 1.40 Å to 1.34 Å ratified the conversion of intermediate L into M. Again, the formation of a covalent bond between the specified atoms leads to activation of the CO2 confirmed by the decrease in bond angle A(25,24,26) from 148.56° to 123.27°. At the same time, H15-O25 bond is elongated from 1.16 Å to 1.47 Å as the proton H15 is transferred from N22 to N12, and the H15–N12 bond formation is confirmed by the decrease in the bond length from 1.40 Å to 1.12 Å. The free energy profile of each stationary point structure combined with some selected resultant kinetic parameters is visualised in Figure 11. This mechanism yields a stable product complex N and the overall reaction of CO2 with aziridine to produce product M in the presence of purine/HI as a catalyst is thermodynamically favourable in the forward direction.