scholarly journals Tracking the Source of Enantioselectivity

2021 ◽  
Author(s):  
◽  
Nina Leeb
Keyword(s):  
Density Functional ◽  
Reaction Pathway ◽  
Transition States ◽  
Basis Set ◽  
Racemic Mixture ◽  
Actual Process ◽  
Resolution Method ◽  
Functional Theory ◽  
Subsequent Investigation ◽  
Efficiency And Effectiveness

<p>Enantioselectivity remains one of synthetic chemistry’s most formidable problems. It arises due to the formation of diastereomeric species in a reaction, either in the form of diastereomeric intermediates or a set of diastereomeric transition states. Without control a racemic mixture is formed. A resolution method is then required to separate the enantiomers. Any given resolution method will rely on the differing energies of diastereomers to allow for their separation. Experimentally there are a myriad of different options that may be used to induce separation; for example chromatography and/or crystallisation. The actual process that occurs through- out this separation has not, however, been fully investigated in all cases. A better understanding of the process is able to provide an understanding of how resolution methods work i.e. when diastereomers occur and how great their energy differences are. This is vital in increasing the efficiency and effectiveness of any given resolution method. This theoretical study completed an investigation of the reaction pathway between the enantiomers of 2-formyl-3-hydroxyl[2.2]paracyclophane (FHPC) with (S)-valyl-(S)-valine. A subsequent investigation of an alternative resolution method, involving (R)-α-PEAM, was also conducted. This latter resolution method was proposed experimentally as a simpler method that could aid in improving the separation of the enantiomers. This investigation was carried out using Density Functional Theory (DFT) with the PBE0 functional and the triple-ζ TZVP basis set. The complete reaction profile was determined and diastereomeric intermediates and transition states for both resolution methods along two different pathways were determined; the ‘N-deprotonation Pathway’ and the ‘O-deprotonation Pathway’. The inadequacy of the first resolution method was found to be due to the presence of copper(II). Furthermore it was discovered that the re- action for both pathways would most likely proceed through the ‘O-deprotonation Pathway’ due to the barriers being lower in energy.</p>

scholarly journals Tracking the Source of Enantioselectivity

2021 ◽  
Author(s):  
◽  
Nina Leeb
Keyword(s):  
Density Functional ◽  
Reaction Pathway ◽  
Transition States ◽  
Basis Set ◽  
Racemic Mixture ◽  
Actual Process ◽  
Resolution Method ◽  
Functional Theory ◽  
Subsequent Investigation ◽  
Efficiency And Effectiveness

<p>Enantioselectivity remains one of synthetic chemistry’s most formidable problems. It arises due to the formation of diastereomeric species in a reaction, either in the form of diastereomeric intermediates or a set of diastereomeric transition states. Without control a racemic mixture is formed. A resolution method is then required to separate the enantiomers. Any given resolution method will rely on the differing energies of diastereomers to allow for their separation. Experimentally there are a myriad of different options that may be used to induce separation; for example chromatography and/or crystallisation. The actual process that occurs through- out this separation has not, however, been fully investigated in all cases. A better understanding of the process is able to provide an understanding of how resolution methods work i.e. when diastereomers occur and how great their energy differences are. This is vital in increasing the efficiency and effectiveness of any given resolution method. This theoretical study completed an investigation of the reaction pathway between the enantiomers of 2-formyl-3-hydroxyl[2.2]paracyclophane (FHPC) with (S)-valyl-(S)-valine. A subsequent investigation of an alternative resolution method, involving (R)-α-PEAM, was also conducted. This latter resolution method was proposed experimentally as a simpler method that could aid in improving the separation of the enantiomers. This investigation was carried out using Density Functional Theory (DFT) with the PBE0 functional and the triple-ζ TZVP basis set. The complete reaction profile was determined and diastereomeric intermediates and transition states for both resolution methods along two different pathways were determined; the ‘N-deprotonation Pathway’ and the ‘O-deprotonation Pathway’. The inadequacy of the first resolution method was found to be due to the presence of copper(II). Furthermore it was discovered that the re- action for both pathways would most likely proceed through the ‘O-deprotonation Pathway’ due to the barriers being lower in energy.</p>

THE H2NO POTENTIAL ENERGY SURFACE EXPLORED WITH HIGH LEVEL AB INITIO AND DENSITY FUNCTIONAL THEORY METHODS

2007 ◽  
Vol 06 (03) ◽  
pp. 549-562
Author(s):  
ABRAHAM F. JALBOUT
Keyword(s):  
Density Functional Theory ◽  
Potential Energy ◽  
Potential Energy Surface ◽  
Density Functional ◽  
Energy Surface ◽  
Hybrid Methods ◽  
Transition States ◽  
Basis Set ◽  
Functional Theory ◽  
High Level

The transition states for the H 2 NO decomposition and rearrangements mechanisms have been explored by the CBS-Q method or by density functional theory. Six transition states were located on the potential energy surface, which were explored with the Quadratic Complete Basis Set (CBS-Q) and Becke's one-parameter density functional hybrid methods. Interesting deviations between the CBS-Q results and the B1LYP density functional theory lead us to believe that further study into this system is necessary. In the efforts to further assess the stabilities of the transition states, bond order calculations were performed to measure the strength of the bonds in the transition state.

A Combined Experimental and Theoretical Study on the Reaction Mechanism and Molecular Structure of 4-(Diphenylamino)-3-iodo-2(5H)-furanone

2017 ◽  
Vol 70 (7) ◽  
pp. 837
Author(s):  
Xiumei Song ◽  
Fuling Xue ◽  
Zongcai Feng ◽  
Yun Wang ◽  
Zhaoyang Wang ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Density Functional ◽  
Reaction Pathway ◽  
Theoretical Calculations ◽  
Calculation Model ◽  
Basis Set ◽  
Functional Theory ◽  
Evaporation Technique ◽  
Molecular Structure Analysis ◽  
Semi Empirical

The simultaneous α-iodination and Nβ-arylation mechanism of 5-alkyloxy-4-phenylamino-2(5H)-furanone by (diacetoxyiodo)benzene was investigated by means of density functional theory (DFT) with B3LYP/6-31G*//LANL2DZ, selecting 4-(diphenylamino)-5-methyloxy-3-iodo-2(5H)-furanone as the calculation model. In addition, the effect of solvent on the reaction pathway was investigated using the Polarisable Continuum Model (PCM). Good agreement was found between the computational and the experimental results. Furthermore, single crystals of 4-(diphenylamino)-5-ethoxy-3-iodo-2(5H)-furanone were grown by slow evaporation technique. The molecular structure analysis was performed by single crystal X-ray analysis and theoretical calculations using a semi-empirical quantum chemical method and DFT/B3LYP methods with a LANL2DZ as basis set.

Investigation on the photodriven catalytic coupling reaction mechanism of p-aminothiophenol on the silver cluster

2015 ◽  
Vol 14 (03) ◽  
pp. 1550019 ◽  
Author(s):  
Lai-Cai Li ◽  
Wei Wang ◽  
Dan Peng ◽  
Rui Pan ◽  
An-Min Tian
Keyword(s):  
Reaction Mechanism ◽  
Density Functional ◽  
Transition States ◽  
Coupling Reaction ◽  
Silver Cluster ◽  
Basis Set ◽  
Functional Theory ◽  
Orbital Interactions ◽  
B3lyp Method ◽  
The Density Functional Theory

The catalytic coupling reaction mechanism for the transformation from p-aminothiophenol (PATP) to 4,4′-dimercaptoazobenzene (4,4′-DMAB) on silver cluster was studied by the density functional theory. All the reactants, intermediates, transition states and products were optimized with B3LYP method at 6-311+G (d, p) basis set (the LanL2DZ basis set was used for Ag atom). Transition states and intermediates have been confirmed by the corresponding vibration analysis and intrinsic reactions coordinate (IRC). In addition, nature bond orbital (NBO) and atoms in molecules (AIM) theories have been used to analyze orbital interactions and bond natures. Consistent with the conclusions reported in the literature, the core of obtaining the production of azobenzene according to the coupling reaction of PATP absorbed on Ag 5 clusters is the elimination of two H atoms. Meanwhile, we find that the effect of illumination in that reaction matters a lot. We also found in PATP molecular that the synergistic catalytic effect of S end absorbed on the catalyzer draws dramatically evident under no illumination conditions, while it draws less obvious under light. According to the paper's conclusion, PATP absorbed on the surface of Ag 5 tends to generate azobenzene easily.

DFT interpretations for cycloadditions of an electron deficient C-aryl-N-phenyl nitrone

2014 ◽  
Vol 13 (01) ◽  
pp. 1450007 ◽  
Author(s):  
Nivedita Acharjee
Keyword(s):  
Density Functional ◽  
Transition States ◽  
Density Functional Theory Calculations ◽  
Basis Set ◽  
Dipolar Cycloaddition ◽  
Functional Theory ◽  
Concerted Mechanism ◽  
Reaction Channels ◽  
Calculated Activation Energy ◽  
Calculated Activation

1,3-dipolar cycloaddition reactions of an electron deficient C-aryl-N-phenyl nitrone to benzylidene derivatives (with different electrophilicities) have been analyzed by density functional theory calculations. The transition states corresponding to the endo and exo approaches along the feasible regioisomeric reaction channels have been located for each cycloaddition. The reactions follow a concerted mechanism with asynchronous transition states. The asynchronicity along the regiochemical reaction modes depends on the β-carbon electrophilicities of the olefins. The regio and stereochemistries predicted from the calculated activation energy barriers (with solvent and higher basis set corrections) of the located transition states are in conformity with the experimental results. The local electrophilicities, softness matching indices and the interaction energies were then calculated to analyze how well these reactivity parameters can interpret the regioselectivities of such reactions. The electronic populations at the reactive sites computed from electrostatic potential-driven atomic charges provided correct and consistent predictions for each theoretical model contrary to the natural orbital based charges.

The ozonolysis of ortho-xylene and its relevance to the history of the benzene problem

2001 ◽  
Vol 79 (8) ◽  
pp. 1278-1283 ◽  
Author(s):  
Saul Wolfe ◽  
Zheng Shi
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Transition States ◽  
Historical Analysis ◽  
Valence Bond ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Initial Attack ◽  
Orbital Theory ◽  
Functional Theory

Using B3LYP density functional theory in conjunction with the 6-311++G** basis set, the relative rates of the initial rate-determining attack of ozone upon the carbon—carbon bonds of o-xylene are found to be 4,5- [Formula: see text] 3,4- > 2,3- > 1,2-. With the assumption that the final products glyoxal (G), methylglyoxal (M), and dimethylglyoxal (D) are determined by the site of the initial attack, and taking statistical factors into account, the ratio G:M:D is calculated to be 3:2:1. This is close to the value found experimentally, and identical to the result predicted by the contention that two nearly equivalent Kekulé–Pauling valence bond (resonance) structures of o-xylene exist and each localized carbon—carbon double bond of these structures is oxidized at the same rate. Although Frontier Molecular Orbital theory also predicts a 3:2:1 ratio of G:M:D, this theory incorrectly predicts that the initial attack of ozone will take place at the 1,2- and 4,5- bonds, with 1,2-attack slightly preferred. These results are discussed in relation to a recent historical analysis of the benzene problem, and it is concluded that since the products of ozonolysis of o-xylene are determined by the relative energies of the transition states leading to the four possible primary ozonides, these transition states should be the focus of theory.Key words: Kekulé structure, resonance, frontier orbital theory, density functional theory, kinetics.

scholarly journals Conversion of methane to benzene in CVI by density functional theory study

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Kun Li ◽  
Hejun Li ◽  
Ningning Yan ◽  
Tiyuan Wang ◽  
Wei Li ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Rate Constants ◽  
Density Functional ◽  
Reaction Pathway ◽  
Chemical Species ◽  
State Theory ◽  
Chemical Vapor Infiltration ◽  
Basis Set ◽  
Functional Theory ◽  
Conversion Of Methane

AbstractA density functional theory (DFT) study was employed to explore the mechanism of the conversion of methane to benzene in chemical vapor infiltration (CVI) based on the concluded reaction pathways from C1-species to C6-species. The geometry optimization and vibrational frequency analysis of all the chemical species and transition states (TS) were performed with B3LYP along with a basis set of 6–311 +G(d, p), and Gaussian 09 software was used to perform the study. The rate constants were calculated by KiSThelP according to the conventional transition state theory (TST), and the Wigner method was applied to acquire the tunneling correction factors. Then the rate constants were fitted to the modified Arrhenius expression in the temperature range of 800–2000 K. As for the barrierless reactions calculated in this paper, the rate constants were selected from the relating references. Through the energetic and kinetic calculations, the most favorable reaction pathway for benzene formation from methane was determined, which were mainly made of the unimolecular dissociation. The conversion trend from C1-species to C4-species is mainly guided by a strong tendency to dehydrogenation and the pathways from C4-species to C6-species are all presumed to be able to produce C6H6 molecule.

Evaluating Transition Metal Barrier Heights with the Latest DFT Exchange–Correlation Functionals – the MOBH35 Benchmark Dataset

2019 ◽  
Author(s):  
Mark Iron ◽  
Trevor Janes
Keyword(s):  
Transition Metal ◽  
Density Functional ◽  
Computational Cost ◽  
Basis Set ◽  
Functional Theory ◽  
Exchange Correlation ◽  
Barrier Heights ◽  
Complete Basis Set ◽  
Complete Basis Set Limit ◽  
Hybrid Functionals

A new database of transition metal reaction barrier heights – MOBH35 – is presented. Benchmark energies (forward and reverse barriers and reaction energy) are calculated using DLPNO-CCSD(T) extrapolated to the complete basis set limit using a Weizmann1-like scheme. Using these benchmark energies, the performance of a wide selection of density functional theory (DFT) exchange–correlation functionals, including the latest from the Truhlar and Head-Gordon groups, is evaluated. It was found, using the def2-TZVPP basis set, that the ωB97M-V (MAD 1.8 kcal/mol), ωB97X-V (MAD 2.1 kcal/mol) and SCAN0 (MAD 2.1 kcal/mol) hybrid functionals are recommended. The double-hybrid functionals PWPB95 (MAD 1.6 kcal/mol) and B2K-PLYP (MAD 1.8 kcal/mol) did perform slightly better but this has to be balanced by their increased computational cost.

Benchmark of Simplified Time-Dependent Density Functional Theory for UV-Vis Spectral Properties of Porphyrinoids

2019 ◽  
Author(s):  
Kamal Batra ◽  
Stefan Zahn ◽  
Thomas Heine
Keyword(s):  
Density Functional Theory ◽  
Density Functional ◽  
Large Scale ◽  
Absolute Error ◽  
Time Dependent ◽  
Basis Set ◽  
Basis Sets ◽  
Functional Theory ◽  
Framework Materials ◽  
Dependent Density

<p>We thoroughly benchmark time-dependent density- functional theory for the predictive calculation of UV/Vis spectra of porphyrin derivatives. With the aim to provide an approach that is computationally feasible for large-scale applications such as biological systems or molecular framework materials, albeit performing with high accuracy for the Q-bands, we compare the results given by various computational protocols, including basis sets, density-functionals (including gradient corrected local functionals, hybrids, double hybrids and range-separated functionals), and various variants of time-dependent density-functional theory, including the simplified Tamm-Dancoff approximation. An excellent choice for these calculations is the range-separated functional CAM-B3LYP in combination with the simplified Tamm-Dancoff approximation and a basis set of double-ζ quality def2-SVP (mean absolute error [MAE] of ~0.05 eV). This is not surpassed by more expensive approaches, not even by double hybrid functionals, and solely systematic excitation energy scaling slightly improves the results (MAE ~0.04 eV). </p>

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