scholarly journals Inter- and Intra-Molecular Organocatalysis of SN2 Fluorination by Crown Ether: Kinetics and Quantum Chemical Analysis

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2947
Author(s):  
Young-Ho Oh ◽  
Wonhyuck Yun ◽  
Chul-Hee Kim ◽  
Sung-Woo Jang ◽  
Sung-Sik Lee ◽  
...  
Keyword(s):  
Crown Ether ◽  
Quantum Chemical ◽  
Metal Salt ◽  
Ion Pair ◽  
Lewis Base ◽  
Free Energies ◽  
Quantum Chemical Analysis ◽  
Rate Acceleration ◽  
Leaving Group

We present the intra- and inter-molecular organocatalysis of SN2 fluorination using CsF by crown ether to estimate the efficacy of the promoter and to elucidate the reaction mechanism. The yields of intramolecular SN2 fluorination of the veratrole substrates are measured to be very small (<1% in 12 h) in the absence of crown ether promoters, whereas the SN2 fluorination of the substrate possessing a crown ether unit proceeds to near completion (~99%) in 12 h. We also studied the efficacy of intermolecular rate acceleration by an independent promoter 18-crown-6 for comparison. We find that the fluorinating yield of a veratrole substrate (leaving group = −OMs) in the presence of 18-crown-6 follows the almost identical kinetic course as that of intramolecular SN2 fluorination, indicating the mechanistic similarity of intra- and inter-molecular organocatalysis of the crown ether for SN2 fluorination. The calculated relative Gibbs free energies of activation for these reactions, in which the crown ether units act as Lewis base promoters for SN2 fluorination, are in excellent agreement with the experimentally measured yields of fluorination. The role of the metal salt CsF is briefly discussed in terms of whether it reacts as a contact ion pair or as a “free” nucleophile F−.

scholarly journals Origin of Salt Effects in SN2 Fluorination Using KF Promoted by Ionic Liquids: Quantum Chemical Analysis

Molecules ◽  
2021 ◽  
Vol 26 (19) ◽  
pp. 5738
Author(s):  
Young-Ho Oh ◽  
Sungyul Lee
Keyword(s):  
Ionic Liquids ◽  
Chemical Analysis ◽  
Quantum Chemical ◽  
Lewis Base ◽  
Quantum Chemical Analysis ◽  
Salt Effects ◽  
Activation Barriers ◽  
Free Energy Of Activation ◽  
Rate Acceleration ◽  
Strong Coulomb

Quantum chemical analysis is presented, motivated by Grée and co-workers’ observation of salt effects [Adv. Synth. Catal. 2006, 348, 1149–1153] for SN2 fluorination of KF in ionic liquids (ILs). We examine the relative promoting capacity of KF in [bmim]PF6 vs. [bmim]Cl by comparing the activation barriers of the reaction in the two ILs. We also elucidate the origin of the experimentally observed additional rate acceleration in IL [bmim]PF6 achieved by adding KPF6. We find that the anion PF6- in the added salt acts as an extra Lewis base binding to the counter-cation K+ to alleviate the strong Coulomb attractive force on the nucleophile F-, decreasing the Gibbs free energy of activation as compared with that in its absence, which is in good agreement with experimental observations of rate enhancement. We also predict that using 2 eq. KF together with an eq. KPF6 would further activate SN2 fluorination.

scholarly journals CHEMISORPTION OF ENROFLOXACIN ON RUTILE-TIO2 (110) SURFACE: A THEORETICAL INVESTIGATION

2019 ◽  
Vol 57 (4) ◽  
pp. 449
Author(s):  
Trung Tien Nguyen ◽  
Tri Ngoc Nguyen ◽  
Dai Quoc Ho
Keyword(s):  
Hydrogen Bond ◽  
Chemical Analysis ◽  
Dft Calculations ◽  
Quantum Chemical ◽  
Adsorption Process ◽  
Stable Configuration ◽  
Quantum Chemical Analysis ◽  
Rutile Tio2 ◽  
The Stability

We investigated the adsorption of enrofloxacin (ENR) antibiotic on rutile-TiO2 (r-TiO2­) (110) surface using DFT calculations. Stable configurations of the adsorption of ENR on r-TiO2 (110) were observed. The origin and role of interactions in stablizing the configurations are thoroughly analyzed using NBO and AIM analyses. Obtained results indicate that the adsorption process is characterized as a strong chemisorption with an associated energy of ca. -35.1 kcal.mol-1 for the most stable configuration. Quantum chemical analysis shows that the stability of configurations is mainly determined by >C=O∙∙∙Ti5f electrostatic interaction along with supplement of H∙∙∙Ob hydrogen bond.

Can the Lewis basicity of an isolated solvent molecule be used for characterizing solvent effects?

2020 ◽  
Vol 16 ◽  
Author(s):  
Jean-François Gal ◽  
Pierre-Charles Maria
Keyword(s):  
Solvent Effects ◽  
Molecular Level ◽  
Solvent Molecule ◽  
Lewis Base ◽  
Bulk Liquid ◽  
Donor Number ◽  
Special Focus ◽  
Solution Processes ◽  
Inert Solvent

Background: The ubiquitous Lewis acid/base interactions are important in solution processes. Analytical chemistry may benefit of a better understanding of the role of Lewis basicity, at the molecular level or acting through a bulk solvent effect. Objective: To clearly delineate (i) the basicity at a molecular level, hereafter referred as solute basicity, and (ii) the solvent basicity, which is a bulk-liquid property. Method: The literature that relates Lewis basicity scales and solvent effects is analyzed. A special focus is placed on two extensive scales, the Donor Number, DN, and the BF3 affinity scale, BF3A, which were obtained by calorimetric measurement on molecules as solutes diluted in a quasi-inert solvent, and therefore define a molecular Lewis basicity. We discuss the validity of these solute scales when regarded as solvent scales, in particular when the basicity of strongly associated liquids is discussed. Results: We demonstrate the drawbacks of confusing the Lewis basicity of a solvent molecule, isolated as solute, and that of the bulk liquid solvent itself. Conclusion: Consequently, we recommend a reasoned use of the concept of Lewis basicity taking clearly into account the specificity of the process for which a Lewis basicity effect may be invoked. In particular, the action of the Lewis base, either as an isolated entity, or as a bulk liquid, must be distinguished.

scholarly journals Dynamics of Oxidation of Reduced Forms of CO2 under Electrochemical and Open-Сircuit Conditions on Polycrystalline Pt in H2CO3

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 274
Author(s):  
Alexander V. Smolin ◽  
Мikhail N. Mikhailov ◽  
Aleksey F. Gadzaov ◽  
Leonid M. Kustov
Keyword(s):  
Quantum Chemical ◽  
Preliminary Analysis ◽  
Oxidation Reaction ◽  
Density Functional ◽  
Oxidation Process ◽  
Open Circuit ◽  
Organic Substances ◽  
Oxidation Of Co ◽  
Reduced Forms

The problem of identifying correlations between catalytic and electrocatalytic processes is one of the fundamental problems of catalysis among “simple” organic substances, and the oxidation of CO and rCO2 is of great interest, since CO and CO2 are considered in pairs both during catalytic and electrocatalytic transformations. In the case of electrocatalysis, this analysis is important in the study of fuel cells. In this paper, we studied the correlation between the oxidation of reduced forms of CO2 (rCO2) under potentiodynamic-galvanoctatic electrochemical and open-circuit conditions of measurements on polycrystalline (pc)Pt in H2CO3. Periodic oscillations are revealed at the oxidation of Had and rCO2 on (pc)Pt. Quantum chemical calculations were carried out on the Pt13 cluster in order to identify the mechanisms of the rCO2 oxidation reaction. The correspondence in the energy parameters of the oxidation process of rCO2 under open-circuit conditions and electrochemical conditions is shown. The preliminary analysis of the system using density functional (DFT) calculations is carried out and the most stable systems that are based on Pt13 are found, namely rOH-Pt13-(CO)n, rOH-Pt13-(COH) and rOH-Pt13-(rCOOH). OH• species was chosen as the most likely candidate for the role of the oxidant for rCO2. Preliminary calculations for the expected reactions were carried out, and the optimal PES is revealed.

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