scholarly journals Substituição nucleofílica alifática: qual o mecanismo preferencial? Estudo computacional dos efeitos da estrutura do substrato e solvente

2020 ◽  
Author(s):  
Bárbara Pereira Peixoto ◽  
José Walkimar de M. Carneiro ◽  
Rodolfo Goetze Fiorot
Keyword(s):  
Density Functional ◽  
Reaction Pathway ◽  
Computational Method ◽  
Reaction Pathways ◽  
Substitution Reactions ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
High Dielectric ◽  
Energy Reaction ◽  
Bimolecular Mechanism

Nucleophilic aliphatic substitution reactions constitute important steps in the synthesis of substances with biological activity and industrial appeal, beyond to participating in steps in biosynthetic routes of natural products. Unimolecular (SN1) and bimolecular (SN2) pathways can be understood as limiting cases of a mechanistic continuum. In between them, borderline mechanisms are proposed. The preference for one path over another depends on several factors, such as the structure of the substrate, the nucleophile and the solvent used. This plurality is still a topic of discussion and needs further understanding. In this context, the present work aims to rationalize the preferential reaction pathway for nucleophilic aliphatic substitutions, whose substrates do not fit only in the uni- and bimolecular models, by identifying lower energy reaction pathways due to the structural and electronic characteristics. The evaluation was carried out by molecular modeling at the Density Functional Theory (DFT) level, simulating substrates with the nucleofuge (Cl and NH3 + ) connected to secondary carbon atoms, with the computational method M06-2X/aug-cc-pVTZ, previously validated according to geometrical and energetic parameters. Besides, we checked the effect of a polar solvent with high dielectric constant in the reaction pathways. The analyzed substrates demonstrated preference for the bimolecular mechanism and the influence of a solvent in these reactions was evident.

scholarly journals Gas Phase Acidities of Organic Acids Based on 9H-Fluorene Scaffold: A DFT Study

2021 ◽  
Author(s):  
Hamid Saeidian ◽  
Baharak Farzin ◽  
Zohreh Mirjafary
Keyword(s):  
Dft Calculations ◽  
Density Functional ◽  
Molecular Electrostatic Potential ◽  
Point Of View ◽  
Computational Method ◽  
Distribution Analysis ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Mineral Acids ◽  
Conjugate Bases

Abstract The density functional theory (DFT) calculations have been performed on a new set of organic Brønsted acids based on 9H-fluorene scaffold. The optimal structures and acidity of the compounds have been calculated by using DFT/B3LYP/6-31++G(d,p) computational method. The acidity of the designed compounds was obtained in the range of 276-328 kcal/mol that the fluorene scaffold bearing ketenimine group 17 and trifilic group 20 with ΔHacid of 276.3 and 285.4 kcal/mol, respectively were found to be within the range of superacids, being more acidic than simple fluorene and mineral acids. The designed compounds and the corresponding conjugate bases were also examined from the aromaticity indices point of view. The tautomerization process for some designed structures was investigated by DFT calculations. Molecular electrostatic potential analysis for the designed acids and the corresponding conjugate bases were also used for charge distribution analysis.

scholarly journals Effect of Constituent Units, Type of Interflavan Bond, and Conformation on the Antioxidant Properties of Procyanidin Dimers: A Computational Outlook

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Ana María Mendoza-Wilson ◽  
René Renato Balandrán-Quintana
Keyword(s):  
Density Functional ◽  
Chemical Potential ◽  
Antioxidant Properties ◽  
Computational Method ◽  
Antioxidant Ability ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Fukui Indices ◽  
Homo Lumo

Procyanidin (PC) dimers are powerful antioxidants, abundant in plant tissues, and also bioavailable. However, the role of the molecular structure of PCs on their antioxidant properties is still a controversial and not fully understood issue that needs to be addressed in a more specific way. The objective of this study was to analyze the effect of the constituent units, type of interflavan bond, and conformation on the antioxidant properties of PC dimers including PB3, PB4, PB5, PB6, PB7, and PB8, using the density functional theory (DFT) computational method. The analysis was performed in function of parameters that allow determining the ability of the molecules to transfer or to capture electrons, among which the chemical potential, bond dissociation enthalpy (BDE), gap energy, Fukui indices, and charge distribution of HOMO-LUMO orbitals. The factors that showed the most notable effects on the antioxidant properties of the PC dimers were the type of interflavan bond and the conformation. The antioxidant ability of the dimers PB3 and PB4 containing the interflavan bond C4–C8, in their Compact conformation, was very similar to each other but greater than those of dimers PB5, PB6, PB7, and PB8 containing the C4–C6 interflavan bond. PB8 showed the lowest antioxidant ability.

Investigation on spin-flip reaction of Re + CH3CN by relativistic density functional theory

2014 ◽  
Vol 43 (25) ◽  
pp. 9508-9517 ◽  
Author(s):  
Yi Xiao ◽  
Wen-Xin Ji ◽  
Wei-Xu Wei-Xu ◽  
Xian-Yang Chen ◽  
Shu-Guang Wang
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Reaction Pathway ◽  
Occupation Number ◽  
Minimal Energy ◽  
Functional Theory ◽  
Spin Flip ◽  
Energy Reaction ◽  
Crossing Point

The minimal energy reaction pathway of Re + CH3CN has been investigated. The minimal energy crossing point is determined with the help of DFT fractional occupation-number (FON) approach.

THEORETICAL STUDY OF OH-INITIATED ATMOSPHERIC OXIDATION FOR PROPYL VINYL ETHER

2009 ◽  
Vol 08 (02) ◽  
pp. 261-277 ◽  
Author(s):  
MAOXIA HE ◽  
HUI WANG ◽  
XIAOYAN SUN ◽  
QINGZHU ZHANG ◽  
WENXING WANG
Keyword(s):  
Vinyl Ether ◽  
Density Functional ◽  
Energy Surface ◽  
Theoretical Study ◽  
Reaction Pathway ◽  
Oh Radicals ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Degradation Reaction ◽  
Total Energies

This paper reports a theoretical study on the reaction of propyl vinyl ether (PVE, CH3CH2CH2OCH=CH2) with OH radicals in the presence of O 2 and NO x. The reaction pathway has been studied with the density functional theory (DFT/B3LYP) at the 6-31G* level. The total energies of all geometries are corrected at the MP2/6-311+G** level. The profile of the potential energy surface was constructed. The possible channels involved in the reaction were discussed. The results show that six product pathways are energetically feasible for the degradation of PVE initiated by OH radicals in the atmosphere. The main products for this degradation reaction are propyl formate, formaldehyde, and glycolic acid propyl ester in which propyl formate and formaldehyde are mainly from the OH addition to C5 atom.

Density functional theory studies of methanol adsorption and decomposition mechanism on Al13 clusters

2014 ◽  
Vol 92 (4) ◽  
pp. 293-298 ◽  
Author(s):  
Cai-Chao Ye ◽  
Feng-Qi Zhao ◽  
Si-Yu Xu ◽  
Xue-Hai Ju
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Reaction Pathways ◽  
Bond Dissociation Energies ◽  
Generalized Gradient ◽  
Aluminum Clusters ◽  
Functional Theory ◽  
Dissociation Energies ◽  
Generalized Gradient Approximation ◽  
The Density Functional Theory

The adsorption and decomposition of the CH3OH molecule on Al13 clusters were investigated by generalized gradient approximation of the density functional theory. The strong attractive forces between the CH3OH molecule and aluminum atoms induce the breaking of the H–O and C–O bonds of CH3OH. Subsequently, the dissociated CH3O and OH radical fragments oxidize the aluminum clusters. The largest adsorption energy is –205.4 kJ/mol. We also investigated five reaction pathways of the CH3OH molecule on the Al13 clusters. The activation energies are in the range of 10.3−113.1 kJ/mol. Compared with the bond dissociation energies of the C–O and O–H bonds in the isolated methanol, Al13 performs very well in decreasing the bond break barrier of CH3OH. In addition, although the C–O bond is slightly weaker than the O−H bond, the O−H bond is even easier to decompose on the Al13 surface. The rate constants of five adsorption paths over the temperature range 300−700 K are presented.

scholarly journals DENSITY FUNCTIONAL THEORY STUDY OF METHANOL ADSORPTION AND DISSOCIATION ON 2Cu/ZnO CATALYST SURFACE

2018 ◽  
Vol 55 (6A) ◽  
pp. 120
Author(s):  
Vo Thanh Cong
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Catalyst Surface ◽  
Reaction Pathway ◽  
Density Functional Theory Study ◽  
Functional Theory ◽  
Methanol Adsorption ◽  
Bond Scission ◽  
The Density Functional Theory ◽  
Adsorption And Dissociation

The adsorption and dissociation of methanol (CH3OH) on the cluster with two copper atoms (2Cu) supported over ZnO catalyst surface were investigated using the density functional theory (DFT). The performance of 2Cu adsorbed on ZnOsurface to obtain model of the 2Cu/ZnO catalyst surface. The most stable site of CH3OH with configuration and energy of adsorption was investigated. The reaction pathway of CH3OH dissociation via bond scission of the O–H, C–H and C–O to form methoxide, hydroxymethyl and methyl was examined, respectively. The obtained calculations pointed out that O–H bond scission is found to be the most favorable pathway on 2Cu/ZnO catalyst surface.

NEW REACTION PATHWAYS OF PROPENE + BCl3 DECOMPOSITION IN CHEMICAL VAPOR DEPOSITION PROCESS

2012 ◽  
Vol 11 (01) ◽  
pp. 53-85 ◽  
Author(s):  
JIANHUA YANG ◽  
KEHE SU ◽  
YAN LIU ◽  
YANLI WANG ◽  
QINGFENG ZENG ◽  
...  
Keyword(s):  
Density Functional ◽  
Chemical Vapor ◽  
Deposition Process ◽  
Reaction Pathways ◽  
Electronic Correlation ◽  
Free Energies ◽  
Functional Theory ◽  
Reaction Coordinates ◽  
The Density Functional Theory ◽  
Correct Reaction

More reaction pathways in the CVD process of preparing boron-carbides with BCl3-C3H6(propene)-H2 precursors were examined in addition to the "lowest" path proposed by Jiang et al. in Theor Chem Acc127:519–538, 2010. The new pathways investigated in this work involve 81 new transition states and 79 new intermediates. Geometries of the species were optimized with the density functional theory at B3PW91/6-311G(d,p) level. Intrinsic reaction coordinates were analyzed to confirm the correct reaction linkages. Energy barriers and reaction energies were calculated with the accurate model chemistry method G3(MP2) after a non-dynamical electronic correlation detection using CASSCF method. Heat capacities and entropies were obtained with the statistical thermodynamics and fitted as a function of temperature. Gibbs free energies at 298.15 K and 1200 K were used to examine the reaction paths. It was found that some steps in the new paths at both 298.15 K and 1200 K are different from the "lowest" path obtained previously and the pathways for the new products CB and C2B were obtained.

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