Theoretical Study of Stereoselectivity for Syn-Selective Cross-Aldol Reactions of Aldehydes Catalyzed by Chiral Diamine Organocatalysts

2013 ◽  
Vol 798-799 ◽  
pp. 59-62
Author(s):  
Cheng Yan Zhao ◽  
Ai Ping Fu ◽  
Hong Liang Li ◽  
Ping Wang ◽  
Yong Xu ◽  
...  
Keyword(s):  
Theoretical Study ◽  
Enantiomeric Excess ◽  
Aldol Reactions ◽  
Quantum Mechanical ◽  
Computational Studies ◽  
Poor Agreement ◽  
Chiral Diamine ◽  
Direct Cross ◽  
The Subject ◽  
Chiral Diamines

Quantum mechanical calculations have been performed to study the stereoselectivities in the direct cross-aldol reactions of aldehydes catalyzed by simple chiral diamines. The detailed computational studies on the stereochemistry-controlling step of the subject reactions have been presented by DFT calculations at the B3LYP/6-31G* level. The poor agreement between the calculated and the observed diastereomeric ratio and enantiomeric excess values is obtained for all diamines catalysts. Further M06-2X calculations can provide a reasonable explanation for the observed syn-selectivities of the asymmetric cross-aldol reaction between propionaldehyde and 4-nitrobenzaldehyde.

Thermodynamics of Flowing Systems: with Internal Microstructure

1994 ◽  
Author(s):  
Antony N. Beris ◽  
Brian J. Edwards
Keyword(s):  
Free Energy ◽  
Theoretical Study ◽  
Flow Behavior ◽  
Irreversible Thermodynamics ◽  
Hamiltonian Mechanics ◽  
Complex Interplay ◽  
Microscopic Models ◽  
Flow Phenomena ◽  
The Subject ◽  
The Continuum

This much-needed monograph presents a systematic, step-by-step approach to the continuum modeling of flow phenomena exhibited within materials endowed with a complex internal microstructure, such as polymers and liquid crystals. By combining the principles of Hamiltonian mechanics with those of irreversible thermodynamics, Antony N. Beris and Brian J. Edwards, renowned authorities on the subject, expertly describe the complex interplay between conservative and dissipative processes. Throughout the book, the authors emphasize the evaluation of the free energy--largely based on ideas from statistical mechanics--and how to fit the values of the phenomenological parameters against those of microscopic models. With Thermodynamics of Flowing Systems in hand, mathematicians, engineers, and physicists involved with the theoretical study of flow behavior in structurally complex media now have a superb, self-contained theoretical framework on which to base their modeling efforts.

ON "PLASTIC" WAVES IN SOLIDS

1959 ◽  
Vol 37 (9) ◽  
pp. 1017-1035 ◽  
Author(s):  
John M. Bowsher
Keyword(s):  
Theoretical Study ◽  
Short Review ◽  
Future Research ◽  
Past Work ◽  
The Past ◽  
Engineering Significance ◽  
The Subject

The study of the propagation of "plastic" waves in solids has reached a stage where it is necessary to consider which direction future research should take. In the past 90 or so years many experiments, mostly designed to elucidate certain points of engineering significance, and a few attempts at a theoretical study have cast some light on the subject and revealed it as one of formidable difficulty.Nearly all the experiments have of necessity relied on rather dubious theories for their interpretation, and part of the present paper will be devoted to a description of an apparatus which gives results capable of being interpreted with a very minimum of theory. The remainder of the paper is devoted to a short review of past work with particular emphasis on basic phenomena and to a brief discussion on the most pressing problems still remaining. The experiments described in the present paper bring to light a factor in the propagation of "plastic" waves that seems to have been overlooked in previous work.

Diastereoselective Addition of α-Metalated Sulfoxides to Imines Revisited: Mechanism, Computational Studies, and the Effect of External Chiral Ligands

2003 ◽  
Vol 68 (5) ◽  
pp. 885-898 ◽  
Author(s):  
Brian Pedersen ◽  
Tobias Rein ◽  
Inger Søtofte ◽  
Per-Ola Norrby ◽  
David Tanner
Keyword(s):  
Reaction Time ◽  
Low Temperature ◽  
Asymmetric Synthesis ◽  
Chiral Ligands ◽  
Quantum Mechanical ◽  
Kinetic Control ◽  
Computational Studies ◽  
Quantum Mechanical Calculations ◽  
Short Reaction Time ◽  
Diastereoselective Addition

Some new results on asymmetric synthesis via the addition of α-metalated methyl tolyl sulfoxides to imines are presented. Good diastereoselectivity (up to >98% d.e. for product 3g) can be obtained under conditions of kinetic control (short reaction time, low temperature). The transition state (a six-membered "flat chair") was probed by quantum mechanical calculations, which underpinned the idea of using external chiral ligands to enhance the diastereoselectivity of otherwise moderately selective reactions. In this way, the diastereomeric ratio of the product 3a could be raised from (84:16) to (>99:1) by use of a readily available C2-symmetric bis(sulfonamide) ligand.

scholarly journals Experimental and theoretical study of Aspartic acid

2019 ◽  
Keyword(s):  
Aspartic Acid ◽  
Single Molecule ◽  
Dft Calculation ◽  
Theoretical Study ◽  
Quantum Mechanical ◽  
Experimental Ir ◽  
Vibrational Bands ◽  
Computational Research ◽  
Ir And Raman ◽  
Dielectric Environment

The aim of this research is to detect zwittterionic structure of the aspartic acid and confirm the experimental spectra with quantum chemical calculations. The experimental IR and Raman spectra of aspartic acid powder show no vibrational bands of OH and NH stretching in expected spectral region. We assume that zwitterionic structure of aspartic acid is responsible for lowering the frequencies of these vibrations. An extensive experimental and computational research supports this assumption. Our DFT calculation strongly suggests the need for the dielectric environment in order to stabilize the zwitterionic structure of a single molecule. The network of intermolecular hydrogen bonding between aspartic acid molecules provides this dielectric environment. The DFT quantum mechanical calculations corroborate this assumption by optimizing a four-member group of molecules, which also gives an explanation of broad IR spectrum lines.

scholarly journals O lúdico como contribuição para a aprendizagem

2016 ◽  
Vol 6 (1) ◽  
pp. 42
Author(s):  
Givoneide Barbosa de Sousa ◽  
José Ozildo dos Santos
Keyword(s):  
Teacher Education ◽  
Learning Process ◽  
Theoretical Study ◽  
Educational Environment ◽  
Different Types ◽  
The Subject

<p>Este artigo aborda como o lúdico, por meio da formação do educador, interfere no processo de aprendizagem. Trata-se de um estudo teórico a respeito das estratégias voltadas para o conceito histórico de criança, concepção sobre o cuidar, fundamentos sobre as instituições escolares. Nele também aborda-se as atividades, nas quais são observados conteúdos que envolvessem as brincadeiras lúdicas e que possibilitam as crianças aprendem com mais facilidade brincando. Demonstrou-se que a ludicidade ajuda no aprimoramento da educação, pode ser crítica e criativa. De acordo com a demanda e realidade da sala de aula, cabe ao educador desenvolve possibilidades que permitam aos educandos possam experimentar situações que interfiram de forma positiva no ensino, tornando-o produtivo. A utilização de jogos e brincadeiras no meio educacional propicia as crianças o aprimoramento de diversos conhecimentos de forma lúdica. Aos educadores, estes além de estarem motivados também com o lúdico, é preciso um conhecimento mais elaborado acerca do tema, para poder intervir nas brincadeiras das crianças. Contudo, faz-se necessário auxiliar a criança, de maneira sutil, para que brinque com diversos tipos de brinquedos.</p><p align="center"><strong><em>The playful</em></strong><strong><em> </em></strong><strong><em>as a contribution to</em></strong><strong><em> </em></strong><strong><em>learning</em></strong><strong><em></em></strong></p><p><strong>Abstract: </strong>This article discusses how the playful, through teacher education, interferes with the learning process. This is a theoretical study on the strategies for the historical concept of child conception of care, fundamentals of the schools. It also covers up the activities in which contents are observed involving the playful banter and enable children learn more easily playing. It was demonstrated that playfulness helps in the improvement of education, can be critical and creative. According to the demand and reality of the classroom, it is the educator develops possibilities that allow students to experience situations that interfere positively in the school, making it productive. The use of games and activities in the educational environment providing children the improvement of diverse knowledge in a playful manner. Educators, these besides being also motivated by the playful, we need a more elaborate knowledge on the subject, to be able to intervene in the games of children. However, it is necessary to help the child, subtly, to play with different types of toys.</p>

Molecular dissociation and proton transfer in aqueous methane solution under electric field.

2021 ◽  
Author(s):  
Giuseppe Cassone ◽  
Jiri Sponer ◽  
Franz Saija
Keyword(s):  
Solar System ◽  
Electric Field ◽  
Proton Transfer ◽  
Computational Studies ◽  
Molecular Dissociation ◽  
The Subject

Methane-water mixtures are ubiquitous in our Solar System and they have been the subject of a wide variety of experimental, theoretical, and computational studies aimed at understanding their behaviour under...

Your EHD Rig May Not Be As Elastohydrodynamic As You Think

2021 ◽  
Vol 143 (8) ◽  
Author(s):  
Scott Bair ◽  
Wassim Habchi
Keyword(s):  
Film Thickness ◽  
Short Note ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Experimental Investigations ◽  
Poor Agreement ◽  
Elastic Regime ◽  
The Poor ◽  
The Subject ◽  
Primary Instrument

Abstract The concentrated contact formed between a steel ball and a glass disc—the optical elastohydrodynamic lubrication (EHD) rig—has been the primary instrument for experimental investigations of elastohydrodynamic film thickness. It has been a source for values of pressure-viscosity coefficient, a difficult-to-define property of liquids. However, comparisons with the pressure dependence of the viscosity obtained in viscometers show little agreement. There are multiple reasons for this failure including shear-thinning and compressibility of the oil. Another reason for the poor agreement is the subject of this short note. The optical EHD rig using glass as one surface will only be in the piezoviscous-elastic (EHD) regime when the pressure-viscosity coefficient is large. For low values, it would be operating in the isoviscous-elastic regime (soft EHD).

Sign in / Sign up

Export Citation Format

Share Document