scholarly journals Computational Study of the Stereoselectivity Profiles of the Diels-Alder Cycloaddition Reactions of Cyclopentadiene and Butadiene with Cyclopropenes

2020 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Theoretical Models ◽  
Diels Alder ◽  
Cycloaddition Reactions ◽  
Free Energies ◽  
Differential Activation ◽  
Activation Free Energy ◽  
The Difference ◽  
First Time

The <i>endo</i> and <i>exo</i> stereoselectivities of the Diels-Alder (DA) cycloaddition reactions of 3,3-disubstituted cyclopropenes with butadiene and cyclopentadiene, the latter for the first time, were investigated by means of density functional and quantum chemical calculations for a comparison. To establish distinction between the selectivites, activation free energies were systematically estimated in the gas phase and also in solvents. The differential activation free energies clearly predict exclusive <i>endo</i> configuration of the products formed from the reaction of the unsubstituted cyclopropene with butadiene and cyclopentadiene. However, the results were found to be markedly different for the substituted cyclopropenes from available experimental selectivities. It was also discovered that butadiene and cyclopentadiene are markedly different in their respective stereospecific product yields, nevertheless the difference between the two was only a methylene group. The failure of the differential activation free energy approach to predict the experimental stereoselectivities of the DA reactions of several perhalocyclopropenes with cyclopentadiene is probably due to yet insufficient development of the various theoretical models dealing with the <i>endo</i> and <i>exo</i> DA preferences.

scholarly journals Computational Study of the Stereoselectivity Profiles of the Diels-Alder Cycloaddition Reactions of Cyclopentadiene and Butadiene with Cyclopropenes

2020 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Theoretical Models ◽  
Diels Alder ◽  
Cycloaddition Reactions ◽  
Free Energies ◽  
Differential Activation ◽  
Activation Free Energy ◽  
The Difference ◽  
First Time

The <i>endo</i> and <i>exo</i> stereoselectivities of the Diels-Alder (DA) cycloaddition reactions of 3,3-disubstituted cyclopropenes with butadiene and cyclopentadiene, the latter for the first time, were investigated by means of density functional and quantum chemical calculations for a comparison. To establish distinction between the selectivites, activation free energies were systematically estimated in the gas phase and also in solvents. The differential activation free energies clearly predict exclusive <i>endo</i> configuration of the products formed from the reaction of the unsubstituted cyclopropene with butadiene and cyclopentadiene. However, the results were found to be markedly different for the substituted cyclopropenes from available experimental selectivities. It was also discovered that butadiene and cyclopentadiene are markedly different in their respective stereospecific product yields, nevertheless the difference between the two was only a methylene group. The failure of the differential activation free energy approach to predict the experimental stereoselectivities of the DA reactions of several perhalocyclopropenes with cyclopentadiene is probably due to yet insufficient development of the various theoretical models dealing with the <i>endo</i> and <i>exo</i> DA preferences.

Computational Study of the Stereoselectivity Profiles of the Diels-Alder Cycloaddition Reactions of Cyclopentadiene and Butadiene with Cyclopropenes

2020 ◽  
Author(s):  
Veejendra Yadav
Keyword(s):  
Density Functional ◽  
Computational Study ◽  
Theoretical Models ◽  
Diels Alder ◽  
Cycloaddition Reactions ◽  
Free Energies ◽  
Differential Activation ◽  
Activation Free Energy ◽  
The Difference ◽  
First Time

The <i>endo</i> and <i>exo</i> stereoselectivities of the Diels-Alder (DA) cycloaddition reactions of 3,3-disubstituted cyclopropenes with butadiene and cyclopentadiene, the latter for the first time, were investigated by means of density functional and quantum chemical calculations for a comparison. To establish distinction between the selectivites, activation free energies were systematically estimated in the gas phase and also in solvents. The differential activation free energies clearly predict exclusive <i>endo</i> configuration of the products formed from the reaction of the unsubstituted cyclopropene with butadiene and cyclopentadiene. However, the results were found to be markedly different for the substituted cyclopropenes from available experimental selectivities. It was also discovered that butadiene and cyclopentadiene are markedly different in their respective stereospecific product yields, nevertheless the difference between the two was only a methylene group. The failure of the differential activation free energy approach to predict the experimental stereoselectivities of the DA reactions of several perhalocyclopropenes with cyclopentadiene is probably due to yet insufficient development of the various theoretical models dealing with the <i>endo</i> and <i>exo</i> DA preferences.

scholarly journals Application of β-Phosphorylated Nitroethenes in [3+2] Cycloaddition Reactions Involving Benzonitrile N-Oxide in the Light of a DFT Computational Study

Organics ◽  
2021 ◽  
Vol 2 (1) ◽  
pp. 26-37
Author(s):  
Karolina Zawadzińska ◽  
Karolina Kula
Keyword(s):  
Density Functional ◽  
Reaction Path ◽  
Computational Study ◽  
Cyano Group ◽  
Cycloaddition Reactions ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Reaction Channels ◽  
One Step ◽  
Step Mechanism

The regiochemistry of [3+2] cycloaddition (32CA) processes between benzonitrile N-oxide 1 and β-phosphorylated analogues of nitroethenes 2a–c has been studied using the Density Functional Theory (DFT) at the M062X/6-31+G(d) theory level. The obtained results of reactivity indices show that benzonitrile N-oxide 1 can be classified both as a moderate electrophile and moderate nucleophile, while β-phosphorylated analogues of nitroethenes 2a–c can be classified as strong electrophiles and marginal nucleophiles. Moreover, the analysis of CDFT shows that for [3+2] cycloadditions with the participation of β-phosphorylatednitroethene 2a and β-phosphorylated α-cyanonitroethene 2b, the more favored reaction path forms 4-nitro-substituted Δ2-isoxazolines 3a–b, while for a reaction with β-phosphorylated β-cyanonitroethene 2c, the more favored path forms 5-nitro-substituted Δ2-isoxazoline 4c. This is due to the presence of a cyano group in the alkene. The CDFT study correlates well with the analysis of the kinetic description of the considered reaction channels. Moreover, DFT calculations have proven the clearly polar nature of all analyzed [3+2] cycloaddition reactions according to the polar one-step mechanism.

scholarly journals Computational Study of Methane C–H Activation by Main Group and Mixed Main Group–Transition Metal Complexes

Molecules ◽  
2020 ◽  
Vol 25 (12) ◽  
pp. 2794
Author(s):  
Carly C. Carter ◽  
Thomas R. Cundari
Keyword(s):  
Transition Metal Complexes ◽  
Active Site ◽  
Density Functional ◽  
Computational Study ◽  
Divalent Metal ◽  
Main Group ◽  
Free Energies ◽  
Functional Theory ◽  
Activation Barriers ◽  
Experimental Values

In the present density functional theory (DFT) research, nine different molecules, each with different combinations of A (triel) and E (divalent metal) elements, were reacted to effect methane C–H activation. The compounds modeled herein incorporated the triels A = B, Al, or Ga and the divalent metals E = Be, Mg, or Zn. The results show that changes in the divalent metal have a much bigger impact on the thermodynamics and methane activation barriers than changes in the triels. The activating molecules that contained beryllium were most likely to have the potential for activating methane, as their free energies of reaction and free energy barriers were close to reasonable experimental values (i.e., ΔG close to thermoneutral, ΔG‡ ~30 kcal/mol). In contrast, the molecules that contained larger elements such as Zn and Ga had much higher ΔG‡. The addition of various substituents to the A–E complexes did not seem to affect thermodynamics but had some effect on the kinetics when substituted closer to the active site.

scholarly journals The difference in stability between 5′R and 5′S diastereomers of 5′,8-cyclopurine-2′-deoxynucleosides. DFT study in gaseous and aqueous phase

2010 ◽  
Vol 8 (1) ◽  
pp. 134-141 ◽  
Author(s):  
Boleslaw Karwowski
Keyword(s):  
Density Functional ◽  
Bond Cleavage ◽  
Basis Set ◽  
Small Range ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Formic Acid Hydrolysis ◽  
The Difference ◽  
The Stability ◽  
First Time

AbstractOxidatively generated damage to DNA frequently appears in the human genome as an effect of aerobic metabolism or as the result of exposure to exogenous oxidizing agents. Due to these facts it has been decided to calculate the stability of 5′,8-cyclo-2′-deoxyadenosine/guanosine (cdA, cdG) in their 5′R and 5′S diastereomeric forms. For all points of quantum mechanics studies presented, the density functional theory (DFT) with B3LYP parameters on 6-311++G** basis set level was used. The calculations showed a significant negative enthalpy for glycosidic bond cleavage reaction for cationic forms and slightly negative for neutral ones. The preliminary study of the discussed process has shown the nature of stepwise nucleophilic substitution DN*AD type mechanism. Surprisingly, the different values in free energy, between short-lived oxacarbenium ion intermediates, have been found to lie over a relatively small range, around 1 and 2.8 kcal mol−1. For anions, the decomposition enthalpies were found as positive in aqueous phases. These theoretical results are supported by the formic acid hydrolysis experiments of both diastereomers of cdA, for the first time. (5′S)cdA exhibited higher stability than (5′R)cdA.

scholarly journals The Role of the Active Site Tyrosine in the Mechanism of Lytic Polysaccharide Monooxygenase

2020 ◽  
Author(s):  
Aina McEvoy ◽  
Joel Creutzberg ◽  
Raushan Kumar Singh ◽  
Morten J. Bjerrum ◽  
Erik Hedegård
Keyword(s):  
Active Site ◽  
Density Functional ◽  
Renewable Resource ◽  
Lytic Polysaccharide Monooxygenase ◽  
Functional Theory ◽  
Polysaccharide Monooxygenases ◽  
Active Site Tyrosine ◽  
The Difference ◽  
First Time

Natural polysaccharides (such as cellulose) comprise a large bio-renewable resource. However, exploitation of this resource requires energy-efficient polysaccharide degradation, which is currently limited by the inherent recalcitrance of many naturally occurring polysaccharides. Catalytic breakdown of polysaccharides can be achieved more efficiently by means of the enzymes lytic polysaccharide monooxygenases (LPMOs). However, the LPMO mechanism has remained controversial, preventing full exploitation of their potential. One of the controversies has centered around an active site tyrosine, present in most LPMOs. Different roles for this tyrosine have been proposed without direct evidence, but two recent investigations have for the first time obtained direct (spectroscopic) evidence for that chemical modification of this tyrosine is possible. Surprisingly, the spectroscopic features obtained in the two investigations are remarkably different. In this paper we use density functional theory (DFT) in a QM/MM formulation to reconcile these (apparently) conflicting results. By modeling the spectroscopy as well as the underlying reaction mechanism we can show how formation of two isomers (both involving deprotonation of tyrosine) explain the difference in the experimental observed spectroscopic features. The link between our structures and the observed spectroscopy provides a firm ground to investigate the role of tyrosine.

Computational study of Cu2ZnSn(X1−xTex)4 (X = S, Se) for optoelectronic applications

2016 ◽  
Vol 30 (22) ◽  
pp. 1650137 ◽  
Author(s):  
Naeem Ullah ◽  
G. Murtaza ◽  
M. A. Iqbal ◽  
Asif Mahmood ◽  
R. Khenata
Keyword(s):  
Optical Properties ◽  
Density Functional ◽  
Computational Study ◽  
Visible Region ◽  
Strong Response ◽  
Functional Theory ◽  
Lattice Constants ◽  
Minimization Procedure ◽  
First Time ◽  
Time Density

The [Formula: see text], [Formula: see text] and [Formula: see text] and their alloys have been frequently investigated experimentally owing to their suitable bandgap for the solar cell applications. For the first time, density functional theory is applied to explore the structural, electronic and optical properties of [Formula: see text] and [Formula: see text] [Formula: see text]. The energy minimization procedure reveals that the Kesterite phase is stable compared to the Stannite structure. Lattice constants of the compounds are in good agreement with the previous experimental results. The alloys have direct bandgaps which decrease by increasing the concentration of Te. The chemical bonding among the cations and anion is dominantly covalent. Electronic bandgap dependent optical properties like absorption coefficient and optical conductivity are studied in detail. The materials show strong response in the visible region of energy spectrum indicating the usefulness of these materials for optoelectronic devices.

scholarly journals Size-dependent trends in the hydrogen evolution activity and electronic structure of MoS2 nanotubes

2021 ◽  
Author(s):  
Charlie Ruffman ◽  
James Thomas Alan Gilmour ◽  
Anna L. Garden
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Hydrogen Evolution ◽  
Density Functional ◽  
Hydrogen Adsorption ◽  
Density Functional Theory Calculations ◽  
Free Energies ◽  
Functional Theory ◽  
Size Dependent ◽  
First Time

The thermodynamics of hydrogen evolution on MoS2 nanotubes is studied for the first time using periodic density functional theory calculations to obtain hydrogen adsorption free energies (ΔGH ads) on pristine...

scholarly journals Organomagnesium Crown Ethers and Their Binding Affinities with Li+, Na+, K+, Be2+, Mg2+, and Ca2+ Ions - a Theoretical Study

2021 ◽  
Author(s):  
Krishnan Thirumoorthy ◽  
Uday Kumar Padidela ◽  
Pothiappan Vairaprakash ◽  
Venkatesan Thimmakondu
Keyword(s):  
Metal Ions ◽  
Crown Ethers ◽  
Density Functional ◽  
Building Blocks ◽  
Binding Energies ◽  
Binding Affinities ◽  
Free Energies ◽  
Delta G ◽  
Cluster Methods ◽  
First Time

Novel organomagnesium crown ether molecules have been computationally characterized for the first time using density functional theory (DFT). Monomer units of MgC6 have been used as building blocks. The potential energy surface of the parent elemental composition, MgC6H2, has been extensively explored using both DFT and coupled-cluster methods. It is concluded that the seven-membered ring isomer, 1-magnesacyclohept-4-en-2,6-diyne, is the thermodynamically most stable molecule at all levels. Thus, the latter has been used as the building block for organomagnesium crown ethers. Both alkali (Li+, Na+, and K+) and alkaline-earth (Be2+, Mg2+, and Ca2+) metal ions selective complexes have been theoretically identified. Binding energies (Delta E at 0 K) and thermally corrected Gibbs free energies (Delta G at 298.15 K) have<br>been computed for these metal ions with MgC6-9-crown-3 and MgC6-12-crown-4 to gauge their binding affinities.Novel organomagnesium crown ether molecules have been computationally characterized for the first time using density functional theory (DFT). Monomer units of MgC6 have been used as building blocks. The potential energy surface of the parent elemental composition, MgC6H2, has been extensively explored using both DFT and coupled-cluster methods. It is concluded that the seven-membered ring isomer, 1-magnesacyclohept-4-en-2,6-diyne, is the thermodynamically most stable molecule at all levels. Thus, the latter has been used as the building block for organomagnesium crown ethers. Both alkali (Li+, Na+, and K+) and alkaline-earth (Be2+, Mg2+, and Ca2+) metal ions selective complexes have been theoretically identified. Binding energies (Delta E at 0 K) and thermally corrected Gibbs free energies (Delta G at 298.15 K) have been computed for these metal ions with MgC6-9-crown-3 and MgC6-12-crown-4 to gauge their binding affinities.

scholarly journals Organomagnesium Crown Ethers and Their Binding Affinities with Li+, Na+, K+, Be2+, Mg2+, and Ca2+ Ions - a Theoretical Study

2021 ◽  
Author(s):  
Krishnan Thirumoorthy ◽  
Uday Kumar Padidela ◽  
Pothiappan Vairaprakash ◽  
Venkatesan Thimmakondu
Keyword(s):  
Metal Ions ◽  
Crown Ethers ◽  
Density Functional ◽  
Building Blocks ◽  
Binding Energies ◽  
Binding Affinities ◽  
Free Energies ◽  
Delta G ◽  
Cluster Methods ◽  
First Time

Novel organomagnesium crown ether molecules have been computationally characterized for the first time using density functional theory (DFT). Monomer units of MgC6 have been used as building blocks. The potential energy surface of the parent elemental composition, MgC6H2, has been extensively explored using both DFT and coupled-cluster methods. It is concluded that the seven-membered ring isomer, 1-magnesacyclohept-4-en-2,6-diyne, is the thermodynamically most stable molecule at all levels. Thus, the latter has been used as the building block for organomagnesium crown ethers. Both alkali (Li+, Na+, and K+) and alkaline-earth (Be2+, Mg2+, and Ca2+) metal ions selective complexes have been theoretically identified. Binding energies (Delta E at 0 K) and thermally corrected Gibbs free energies (Delta G at 298.15 K) have<br>been computed for these metal ions with MgC6-9-crown-3 and MgC6-12-crown-4 to gauge their binding affinities.Novel organomagnesium crown ether molecules have been computationally characterized for the first time using density functional theory (DFT). Monomer units of MgC6 have been used as building blocks. The potential energy surface of the parent elemental composition, MgC6H2, has been extensively explored using both DFT and coupled-cluster methods. It is concluded that the seven-membered ring isomer, 1-magnesacyclohept-4-en-2,6-diyne, is the thermodynamically most stable molecule at all levels. Thus, the latter has been used as the building block for organomagnesium crown ethers. Both alkali (Li+, Na+, and K+) and alkaline-earth (Be2+, Mg2+, and Ca2+) metal ions selective complexes have been theoretically identified. Binding energies (Delta E at 0 K) and thermally corrected Gibbs free energies (Delta G at 298.15 K) have been computed for these metal ions with MgC6-9-crown-3 and MgC6-12-crown-4 to gauge their binding affinities.

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