The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Shuji Tomoda - One of the best experts on this subject based on the ideXlab platform.
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the danishefsky pyranone puzzle an explanation based on the exterior Frontier Orbital extension model
Tetrahedron Letters, 2009Co-Authors: Daisuke Kaneno, Shuji TomodaAbstract:Abstract The unusual facial stereoselection in the hydride reduction of the Danishefsky pyranones (2,3,5,6-tetrahydro-4-pyranones) with L-Selectride (Li-sec-Bu3BH) has been explained based on the exterior Frontier Orbital extension model (the EFOE model).
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prediction of facial diastereoselection with the exterior Frontier Orbital extension model efoe model
Journal of Synthetic Organic Chemistry Japan, 2001Co-Authors: Shuji Tomoda, Daisuke KanenoAbstract:Based on the simple assumption that π-facial diastereoselection should be originated from the difference in the magnitude of the reaction driving force over the two faces of the π-plane, a new theoretical model is proposed for the prediction of faical diastereoselection. According to the Salem-Klopman equation, two quantities - steric effects (1st term) and the spatial extension of Frontier Orbital of a substrate ketone (3rd term) - are quantitatively evaluated as the π-plane-divided accessible space (PDAS) and the exterior Frontier Orbital extension density (EFOE density). The latter is obtained by integrating the Frontier Orbital (LUMO of a ketone) extension over one side of the π-plane in the exterior area of the van der Waals surface of the ketone under the specific criteria that the driving force vector located on the hydride should be maximally directed toward the carbonyl carbon. Numerous cases of facial diastereoselectivity of hydride reduction including ketones with polar substituents, heterocyclic systems, symmetric bi- or tricyclic ketones, imines, iminium ion are successfully explained by these two new simple quantities. These results as well as quantitative evaluation of transition effects (mainly the antiperiplanar hyperconjugative stabilization involving the incipient bond) strongly suggest that the Orbital interaction between reactants generated in the initial stage rather than transition state effects must be the essential process of diastereoselection.
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π facial diastereoselection of hydride reduction of 1 3 diheteran 5 ones application of the exterior Frontier Orbital extension model
Heteroatom Chemistry, 2001Co-Authors: Daisuke Kaneno, Jian Zhang, Michio Iwaoka, Shuji TomodaAbstract:To obtain further evidence for the importance of the ground state conformational and Orbital properties in π-facial diastereoselection of 1,3-diheteran-5-ones (heteroatom = O, S, Se), 2-phenyl-1,3-diselenan-5-one (3a) has been synthesized, and its π-facial diastereoselection upon hydride reduction has been examined. The experimental data of π-facial stereoselection of 3a has been successfully rationalized by the exterior Frontier Orbital extension model (the EFOE model). Intrinsic reaction coordinate (IRC) and natural bond Orbital (NBO) analyses of transition states of LiAlH4 reduction of this ketone have strongly indicated that the transition state effects (the torsional strain of the carbonyl moieties and the antiperiplanar effects involving the incipient bond proposed by the conventional theoretical models for π-facial diastereoselection; the Felkin-Anh model and the Cieplak model) are not responsible for facial selection. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:358–368, 2001
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Reversal of π-facial diastereoselection in the hydride reduction of selenanones. Further application of the exterior Frontier Orbital extension model
Tetrahedron Letters, 2000Co-Authors: Shuji Tomoda, Daisuke Kaneno, Jian Zhang, Masahito Segi, Aojia ZhouAbstract:Abstract Reversal of π-facial diastereoselection in the hydride reduction of 2-phenyl-4-selenanone ( 1b ) and 6-phenyl-3-selenanone ( 2b ) has been rationalized by the exterior Frontier Orbital extension model (EFOE model).
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Origin of π-Facial Stereoselectivity in Nucleophilic Additions. Application of the Exterior Frontier Orbital Extension Model to Imines and Iminium Ions
Journal of Organic Chemistry, 1999Co-Authors: Shuji Tomoda, Takatoshi Senju, Mitsuhiro Kawamura, Takafumi IkedaAbstract:The experimental data of π-facial stereoselection of the imines and the iminium ions of cyclohexanone, tropinone, and adamantan-2-ones have been explained by the exterior Frontier Orbital extension model (EFOE model) previously proposed. In all cases, facial difference in the π-plane-divided accessible space (PDAS), which represents simple summation of the π-plane-divided exterior three-dimensional space nearest to the reaction center outside the van der Waals surface, significantly depends on the structure of the imino moieties. In particular the formation of iminium salt significantly affects the magnitude of both the EFOE density and the PDAS values.
Weitao Yang - One of the best experts on this subject based on the ideXlab platform.
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Orbital relaxation effects on Kohn–Sham Frontier Orbital energies in density functional theory
Journal of Chemical Physics, 2015Co-Authors: Dadi Zhang, Xiao Zheng, Chen Li, Weitao YangAbstract:We explore effects of Orbital relaxation on Kohn–Sham Frontier Orbital energies in density functional theory by using a nonempirical scaling correction approach developed in Zheng et al. [J. Chem. Phys. 138, 174105 (2013)]. Relaxation of Kohn–Sham Orbitals upon addition/removal of a fractional number of electrons to/from a finite system is determined by a systematic perturbative treatment. The information of Orbital relaxation is then used to improve the accuracy of predicted Kohn–Sham Frontier Orbital energies by Hartree–Fock, local density approximation, and generalized gradient approximation methods. The results clearly highlight the significance of capturing the Orbital relaxation effects. Moreover, the proposed scaling correction approach provides a useful way of computing derivative gaps and Fukui quantities of N-electron finite systems (N is an integer), without the need to perform self-consistent-field calculations for (N ± 1)-electron systems.
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Orbital relaxation effects on kohn sham Frontier Orbital energies in density functional theory
Journal of Chemical Physics, 2015Co-Authors: Dadi Zhang, Xiao Zheng, Chen Li, Weitao YangAbstract:We explore effects of Orbital relaxation on Kohn–Sham Frontier Orbital energies in density functional theory by using a nonempirical scaling correction approach developed in Zheng et al. [J. Chem. Phys. 138, 174105 (2013)]. Relaxation of Kohn–Sham Orbitals upon addition/removal of a fractional number of electrons to/from a finite system is determined by a systematic perturbative treatment. The information of Orbital relaxation is then used to improve the accuracy of predicted Kohn–Sham Frontier Orbital energies by Hartree–Fock, local density approximation, and generalized gradient approximation methods. The results clearly highlight the significance of capturing the Orbital relaxation effects. Moreover, the proposed scaling correction approach provides a useful way of computing derivative gaps and Fukui quantities of N-electron finite systems (N is an integer), without the need to perform self-consistent-field calculations for (N ± 1)-electron systems.
Zakya H Kafafi - One of the best experts on this subject based on the ideXlab platform.
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Photoemission study of Frontier Orbital alignment at a metal–organic interface as a function of conjugation length of oligothiophene derivatives
Applied Physics Letters, 2001Co-Authors: Antti J Makinen, Ian G Hill, Tetsuya Noda, Yasuhiko Shirota, Zakya H KafafiAbstract:We report an ultraviolet photoemission spectroscopy (UPS) study of solid films of two molecules, 5,5′-bis(dimesitylboryl)-2,2′-bithiophene (BMB-2T) and 5,5′-bis(dimesitylboryl)-2,2′:5′2′terthiophene (BMB-3T) which have been characterized as potential electron transport materials in organic light-emitting devices. Using the Frontier Orbital positions at a metal-organic interface, determined from the UPS measurements, together with the optical band gaps of the molecules, the electron injection barriers for the two oligothiophene derivatives are found to be significantly different. This barrier is estimated to be ∼0.2-0.3 eV lower for BMB-2T than for BMB-3T at a metal–organic interface.
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photoemission study of Frontier Orbital alignment at a metal organic interface as a function of conjugation length of oligothiophene derivatives
Applied Physics Letters, 2001Co-Authors: Antti J Makinen, Ian G Hill, Tetsuya Noda, Yasuhiko Shirota, Zakya H KafafiAbstract:We report an ultraviolet photoemission spectroscopy (UPS) study of solid films of two molecules, 5,5′-bis(dimesitylboryl)-2,2′-bithiophene (BMB-2T) and 5,5′-bis(dimesitylboryl)-2,2′:5′2′terthiophene (BMB-3T) which have been characterized as potential electron transport materials in organic light-emitting devices. Using the Frontier Orbital positions at a metal-organic interface, determined from the UPS measurements, together with the optical band gaps of the molecules, the electron injection barriers for the two oligothiophene derivatives are found to be significantly different. This barrier is estimated to be ∼0.2-0.3 eV lower for BMB-2T than for BMB-3T at a metal–organic interface.
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organic semiconductor interfaces discrimination between charging and band bending related shifts in Frontier Orbital line up measurements with photoemission spectroscopy
Journal of Applied Physics, 1999Co-Authors: R Schlaf, Charles D Merritt, Lisa A Crisafulli, Zakya H KafafiAbstract:Gaq3 is a promising luminescent organic semiconductor for applications in organic light emitting diodes. The Frontier Orbital alignment at the tris (8-hydroxyquinolinato) gallium (Gaq3)/Pt organic Schottky contact was determined by combined x-ray and ultraviolet photoemission spectroscopy (XPS, UPS) measurements. A Gaq3 thin film was deposited in several steps on a previously Ar+ sputtered pure Pt foil. After each growth step, the sample was characterized by XPS and UPS. The combination of XPS and UPS measurements allows the precise evaluation of the interface dipole independent from the simultaneously occurring band bending at the interface and charging artifacts. The measurements show that the Pt/Gaq3 interface has a strong dipole of 0.71 eV indicating the transfer of negative charge from Gaq3 to Pt. Due to the large work function difference between Pt and Gaq3, strong band bending occurred. At Gaq3 coverages higher than 128 A strong charging shifts occurred in the overlayer related emission lines which...
Victor S Batista - One of the best experts on this subject based on the ideXlab platform.
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Hammett neural networks: prediction of Frontier Orbital energies of tungsten–benzylidyne photoredox complexes
Chemical Science, 2019Co-Authors: Alexander M Chang, Jessica G Freeze, Victor S BatistaAbstract:The successful application of Hammett parameters as input features for regressive machine learning models is demonstrated and applied to predict energies of Frontier Orbitals of highly reducing tungsten–benzylidyne complexes of the form W(CArR)L4X. Using a reference molecular framework and the meta- and para-substituent Hammett parameters of the ligands, the models predict energies of Frontier Orbitals that correlate with redox potentials. The regressive models capture the multivariate character of electron-donating trends as influenced by multiple substituents even for non-aryl ligands, harnessing the breadth of Hammett parameters in a generalized model. We find a tungsten catalyst with tetramethylethylenediamine (tmeda) equatorial ligands and axial methoxyl substituents that should attract significant experimental interest since it is predicted to be highly reducing when photoactivated with visible light. The utilization of Hammett parameters in this study presents a generalizable and compact representation for exploring the effects of ligand substitutions.
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hammett neural networks prediction of Frontier Orbital energies of tungsten benzylidyne photoredox complexes
Chemical Science, 2019Co-Authors: Alexander M Chang, Jessica G Freeze, Victor S BatistaAbstract:The successful application of Hammett parameters as input features for regressive machine learning models is demonstrated and applied to predict energies of Frontier Orbitals of highly reducing tungsten–benzylidyne complexes of the form W(CArR)L4X. Using a reference molecular framework and the meta- and para-substituent Hammett parameters of the ligands, the models predict energies of Frontier Orbitals that correlate with redox potentials. The regressive models capture the multivariate character of electron-donating trends as influenced by multiple substituents even for non-aryl ligands, harnessing the breadth of Hammett parameters in a generalized model. We find a tungsten catalyst with tetramethylethylenediamine (tmeda) equatorial ligands and axial methoxyl substituents that should attract significant experimental interest since it is predicted to be highly reducing when photoactivated with visible light. The utilization of Hammett parameters in this study presents a generalizable and compact representation for exploring the effects of ligand substitutions.
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single molecule rectification induced by the asymmetry of a single Frontier Orbital
Journal of Chemical Theory and Computation, 2014Co-Authors: Wendu Ding, Christian F A Negre, Leslie Vogt, Victor S BatistaAbstract:A mechanism for electronic rectification under low bias potentials is elucidated for the prototype molecule HS-phenyl-amide-phenyl-SH. We apply density functional theory (DFT) combined with the nonequilibrium Green’s function formalism (NEGF), as implemented in the TranSIESTA computational code to calculate transport properties. We find that a single Frontier Orbital, the closest to the Fermi level, provides the dominant contribution to the overall transmission and determines the current. The asymmetric distribution of electron density in that Orbital leads to rectification in charge transport due to its asymmetric response, shifting toward (or away from) the Fermi level under forward (or reverse) applied bias voltage. These findings provide a simple design principle to suppress recombination in molecular assemblies of dye-sensitized solar cells (DSSCs) where interfacial electron transfer is mediated by Frontier Orbitals with asymmetric character.
Brian W. Clare - One of the best experts on this subject based on the ideXlab platform.
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the Frontier Orbital phase angles novel qsar descriptors for benzene derivatives applied to phenylalkylamine hallucinogens
Journal of Medicinal Chemistry, 1998Co-Authors: Brian W. ClareAbstract:A new empirical electronic descriptor, obtained from a molecular Orbital calculation and applicable to benzene derivatives, is proposed. It is shown that this descriptor, the Frontier Orbital phase angle, correlates very strongly with the pharmacological activity in humans of a large series of hallucinogenic phenethylamines. In the largest QSAR study on such hallucinogens yet reported, it is demonstrated that the phase of mixing of degenerate Frontier Orbitals of benzene to form the Frontier Orbitals of the drug results in the best electronic descriptor yet found for hallucinogenic activity in phenylalkylamines.
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Charge transfer complexes and Frontier Orbital energies in QSAR: a congeneric series of electron acceptors
Journal of Molecular Structure-theochem, 1995Co-Authors: Brian W. ClareAbstract:Abstract The calculated stabilities of complexes of methylbenzenes with substituted derivatives of tetracyanoquinodimethane (TCNQ) have been shown to correlate with the highest occupied molecular Orbital (HOMO) energies of the donor methylbenzenes and the lowest unoccupied molecular Orbital (LUMO) energies of the acceptor TCNQ derivatives, calculated by the semi-empirical parametric method 3 (PM3). Thus the Frontier Orbital energies, calculated by this method, which are typical of those used by medicinal chemists, may serve as an indicator of formation of charge transfer complexes, by donating in the case of the HOMO energy, or by accepting in the case of the LUMO, electrons. However, this is so only in the case of unusually strong electron donors or acceptors.
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The relationship of charge transfer complexes to Frontier Orbital energies in QSAR
Journal of Molecular Structure-theochem, 1995Co-Authors: Brian W. ClareAbstract:Abstract Frontier Orbital energies, calculated by fast and approximate semiempirical methods, are widely used as molecular descriptors in medicinal chemistry. The traditional justification is that they represent measures of the ability of drug molecules to participate in the formation of charge transfer complexes. For both theoretical reasons and as a consequence of the drastic approximations inherent in the semiempirical methods, some doubt exists about the basis of this assumption. A computational study has been made of the stability of charge transfer complexes of benzene and methylated benzenes with four electron acceptors by the semiempirical PM3 method. The results support the traditional view that the energy of the highest occupied molecular Orbital of the donor molecule is an indicator of the ability of the donor to form charge transfer complexes with electron acceptors. It was found that the heat of formation of the complex could be calculated, which correlated well with the measured stability constant of the complex, taken from the literature, and with measures of transfer of charge in both the ground state and excited state. The energy of the lowest unoccupied molecular Orbital of the complex, calculated by PM3, was an extremely good measure of the ability of the donor-acceptor pair to form such a complex.
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Frontier Orbital energies in quantitative structure-activity relationships: A comparison of quantum chemical methods
Theoretica chimica acta, 1994Co-Authors: Brian W. ClareAbstract:The energies of the highest occupied and lowest unoccupied molecular Orbitals (HOMO and LUMO) have long been used as descriptors in QSAR (Quantitative Structure-Activity Relationships). It is shown that different quantum chemical methods of calculating these energies yield results which sometimes correlate poorly with each other. This could seriously affect physical interpretation of QSAR equations. A comparison is made between HOMO and LUMO energies and their differences and sums (hardness and electronegativity) calculated by some of the best known ab initio and semi-empirical methods for two series of simple organic molecules. The difference between the HOMO and LUMO energies correlates better between methods than does either alone, and their sum correlates relatively poorly. MINDO/3 (Modified Intermediate Neglect of Differential Overlap, version 3) is the poorest method in terms of correlation with the more extended basis set ab initio methods, followed by CNDO (Complete Neglect of Differential Overlap) and INDO (Intermediate Neglect of Differential Overlap). The best semi-empirical methods, in terms of correlation with experiment and the more extended basis set ab initio calculations, are MNDO (Modified Neglect of Differential Overlap), AM1 (Austin Model 1) and PM3 (Parametric Method 3). The simplest ab initio method, STO-3G, does not agree as well with the extended basis set calculations or with experimental results as the more advanced semi-empirical methods.
