The Experts below are selected from a list of 2433 Experts worldwide ranked by ideXlab platform
Oliver Trapp - One of the best experts on this subject based on the ideXlab platform.
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Asymmetric Induction and Amplification in Stereodynamic Catalytic Systems by Noncovalent Interactions
Synlett, 2020Co-Authors: Jan Felix Scholtes, Oliver TrappAbstract:The local transmission of chiral information by noncovalent interactions is one of the most fundamental processes broadly found in nature, i.e. in complex biochemical systems. This review summarizes our accomplishments in investigating chiral induction in stereodynamic ligands and catalysts by weak intermolecular interactions. It includes our efforts to characterize numerous stereodynamic compounds in detail with respect to their thermodynamic and kinetic properties. Furthermore, many stereolabile ligands for enantioselective catalysis are described, where directed stereoinduction afforded highly enantio- or diastereoenriched catalysts for subsequent selective asymmetric transformations. Various approaches for the dynamic enrichment of one of the catalyst’s conformers are presented, such as noncovalent interaction of the ligand with a chiral environment or a chiral solute. Finally, successful chemical systems are presented in which a process of chiral induction can be coupled with an autoinductive mechanism triggered by the chirality of its own reaction product, realizing Nature-inspired feedback loops resulting in self-amplifying, enantioselective catalytic reactions. 1 Introduction 2 Mapping the Stereodynamic Landscape 3 Chiral Induction by Noncovalent Interactions 4 Autoinduction and Chiral Amplification 5 Self-Alignment and Emergence of Chirality 6 Conclusion
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Stereodynamic tetrahydrobiisoindole "NU-BIPHEP(O)"s: functionalization, rotational barriers and non-covalent interactions.
Beilstein journal of organic chemistry, 2016Co-Authors: Golo Storch, Sebastian Pallmann, Frank Rominger, Oliver TrappAbstract:Stereodynamic ligands offer intriguing possibilities in enantioselective catalysis. "NU-BIPHEPs" are a class of stereodynamic diphosphine ligands which are easily accessible via rhodium-catalyzed double [2 + 2 + 2] cycloadditions. This study explores the preparation of differently functionalized "NU-BIPHEP(O)" compounds, the characterization of non-covalent adduct formation and the quantification of enantiomerization barriers. In order to explore the possibilities of functionalization, we studied modifications of the ligand backbone, e.g., with 3,5-dichlorobenzoyl chloride. Diastereomeric adducts with Okamoto-type cellulose derivatives and on-column deracemization were realized on the basis of non-covalent interactions. Enantioselective dynamic HPLC (DHPLC) allowed for the determination of rotational barriers of ΔG (‡) 298K = 92.2 ± 0.3 kJ mol(-1) and 99.5 ± 0.1 kJ mol(-1) underlining the stereodynamic properties of "NU-BIPHEPs" and "NU-BIPHEP(O)s", respectively. These results make the preparation of tailor-made functionalized stereodynamic ligands possible and give an outline for possible applications in enantioselective catalysis.
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Enantiomerization of Allylic Trifluoromethyl Sulfoxides Studied by HPLC Analysis and DFT Calculations.
Chirality, 2015Co-Authors: Laetitia Bailly, Emilie Petit, Mayaka Maeno, Pascal Cardinael, Isabelle Chataigner, Norio Shibata, Oliver Trapp, Dominique CahardAbstract:Enantiomerization of allylic trifluoromethyl sulfoxides occurs spontaneously at room temperature through the corresponding allylic trifluoromethanesulfenates via a [2,3]-sigmatropic rearrangement. Dynamic enantioselective high-performance liquid chromatography (HPLC) analysis revealed the Stereodynamics of these sulfoxides ranging from chromatographic resolution to peak coalescence at temperatures between 5 and 53 °C. The rate constant of enantiomerization and activation parameters were determined and compared with Density Functional Theory (DFT) calculations.
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A Combined Experimental and Theoretical Study on the Stereodynamics of Monoaza[5]helicenes: Solvent-Induced Increase of the Enantiomerization Barrier in 1-Aza-[5]helicene.
Chemistry – A European Journal, 2015Co-Authors: Tullio Caronna, Andrea Mele, Antonino Famulari, Daniele Mendola, Francesca Fontana, Markus Juza, Matthias Kamuf, Kerstin Zawatzky, Oliver TrappAbstract:Helicenes and heterohelicenes are attractive compounds with great potential in materials sciences to be used in optoelectronics as ligand backbones in enantioselective catalysis and as chiral sensors. The properties of these materials are related to the Stereodynamics of these helical chiral compounds. However, little is known about features controlling Stereodynamics in helicenes; in particular, for heterohelicenes the position of the heteroatom could be relevant in this respect. Herein the complete stereodynamic characterization of monoaza[5]helicenes is shown by enantioselective dynamic HPLC and DFT calculations. At variance with previous theoretical calculations, 1-aza[5]helicene shows a surprisingly high enantiomerization barrier, which is triggered by specific solvent interactions.
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Stereodynamics of small 1 2 dialkyldiaziridines
Chirality, 2013Co-Authors: Matthias Kamuf, Oliver TrappAbstract:Diaziridines are very interesting representatives of organic compounds containing stereogenic nitrogen atoms. In particular, 1,2-dialkyldiaziridines show extraordinarily high stereointegrity. The lone electron pairs of the nitrogen atoms are in trans configuration, avoiding a four-electron repulsive interaction. Furthermore, the trans configuration of the substituents at the nitrogen atoms is energetically favored because of reduced steric interactions. Therefore only two stereoisomers (enantiomers) are observed. At elevated temperatures the enantiomers are interconverting because of the limited stereointegrity of the chirotopic nitrogen atoms. The enantiomerization rate constants and the activation parameters of interconversion are of great interest. Here, we investigated the Stereodynamics of a set of small 1,2-dialkyldiaziridines bearing short substituents (Me, Et, iPr, tBu), using enantioselective dynamic gas chromatography (DGC). Separation of enantiomers of all compounds, including the highly volatile 1,2-dimethyldiaziridine, was achieved using heptakis(2,3-di-O-ethyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin in 50% PS086 (w/w) as chiral stationary phase in fused silica capillaries with a length of up to 50 m. Measurements at variable temperatures were performed and reaction rate constants were determined using the unified equation of chromatography implemented in the software DCXplorer. The activation barriers at room temperature for 1-(tert-butyl)-2-ethyldiaziridine, ΔG╪298K = 123.8 kJ mol–1 (ΔH╪ = 115.5 ± 2.9 kJ mol–1, ΔS╪ = –28 ± 1 J mol–1 K–1), and 1-ethyl-2-isopropyldiaziridine, ΔG╪298K = 124.2 kJ mol–1 (ΔH╪ = 113.1 ± 2.4 kJ mol–1, ΔS╪ = –37 ± 2 J mol–1 K–1), were determined, representing some of the highest values observed for nitrogen inversion in diaziridines. Chirality 00:000–000, 2013. © 2013 Wiley Periodicals, Inc.
Naduvalath Balakrishnan - One of the best experts on this subject based on the ideXlab platform.
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Stereodynamics of ultracold rotationally inelastic collisions.
The Journal of chemical physics, 2020Co-Authors: Masato Morita, Naduvalath BalakrishnanAbstract:Recent experiments on rotational quenching of HD in the v = 1, j = 2 rovibrational state in collisions with H2, D2, and He near 1 K have revealed strong stereodynamic preference stemming from isolated shape resonances. So far, the experiments and subsequent theoretical analyses have considered the initial HD rotational state in an orientation specified by the projection quantum number m or a coherent superposition of different m states. However, it is known that such stereodynamic control is generally not effective in the ultracold energy regime due to the dominance of the incoming s-wave (l = 0, partial wave). Here, we provide a detailed analysis of the Stereodynamics of rotational quenching of HD by He with both m and m' resolution, where m' refers to the inelastically scattered HD. We show the existence of a significant m dependence in the m'-resolved differential and integral cross sections even in the ultracold s-wave regime with a factor greater than 60 for j = 2 → j' = 1 and a factor greater than 1300 for j = 3 → j' = 2 transitions. In the helicity frame, however, the integral cross section has no initial orientation (k) dependence in the ultracold energy regime, even resolving with respect to the final orientation (k'). The distribution of final rotational state orientations (k') is found to be statistical (uniform), regardless of the initial orientation.
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Stereodynamics of rotationally inelastic scattering in cold He+HD collisions.
The Journal of chemical physics, 2020Co-Authors: Masato Morita, Naduvalath BalakrishnanAbstract:Stereodynamics of cold collisions has become a fertile ground for quantized studies of molecular collisions and control of the collision outcome. A benchmark process for stereodynamic control is rotational transition in He+HD collisions. This process was recently probed experimentally by Perreault et al. by examining quenching from $j=2$ to $j'=0$ state in the $v=1$ vibrational manifold. Here, through explicit quantum scattering calculations on a highly accurate ab initio interaction potential for He+H$_2$, we reveal how a combination of two shape resonances arising from $l=1$ and $l=2$ partial waves controls the stereodynamic outcome rather than a single $l=2$ partial wave attributed in the experiment. Further, for collision energies below 0.5 cm$^{-1}$, it is shown that stereodynamic preference for integral cross section follows a simple universal trend.
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Stereodynamics of rotationally inelastic scattering in cold he hd collisions
Journal of Chemical Physics, 2020Co-Authors: Masato Morita, Naduvalath BalakrishnanAbstract:Stereodynamics of cold collisions has become a fertile ground for sensitive probe of molecular collisions and control of the collision outcome. A benchmark system for stereodynamic control of rotational transition is He + HD. This system was recently probed experimentally by Perreault et al. by examining quenching from j = 2 to j′ = 0 state in the v = 1 vibrational manifold of HD. Here, through explicit quantum scattering calculations on a highly accurate ab initio interaction potential for He + H2, we reveal how a combination of two shape resonances arising from l = 1 and l = 2 partial waves controls the stereodynamic outcome rather than a single l = 2 partial wave attributed in the experiment. Furthermore, for collision energies below 0.5 cm−1, it is shown that stereodynamic preference for the integral cross section follows a simple universal trend.
Magnus Gustafsson - One of the best experts on this subject based on the ideXlab platform.
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Erratum: “Observing the Stereodynamics of chemical reactions using randomly oriented molecular beams” [J. Chem. Phys.124, 241105 (2006)]
The Journal of Chemical Physics, 2006Co-Authors: Magnus Gustafsson, Rex T. Skodje, Jianyang Zhang, Dongxu Dai, Steven A. Harich, Xiuyan Wang, Xueming YangAbstract:A new method is demonstrated to study the Stereodynamics of simple chemical reactions that does not require the use of oriented (or aligned) molecular beams or measurements of the orientation state ...
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Probing Stereodynamics in reactive collisions using helicity filtering
Chemical Physics Letters, 2006Co-Authors: Magnus Gustafsson, Rex T. SkodjeAbstract:Abstract Stereodynamic effects in the D + H 2 reaction are studied using a new method that permits reagent-helicity dependent cross sections to be inferred from the scattering results obtained using randomly oriented reagent molecules. Employing fully converged quantum scattering calculations as a benchmark, it is demonstrated that the method yields useful results for all the helicity states corresponding to j = 1 and 2 of the H 2 diatom.
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Observing the Stereodynamics of chemical reactions using randomly oriented molecular beams
The Journal of chemical physics, 2006Co-Authors: Magnus Gustafsson, Rex T. Skodje, Jianyang Zhang, Dongxu Dai, Steven A. Harich, Xiuyan Wang, Xueming YangAbstract:A new method is demonstrated to study the Stereodynamics of simple chemical reactions that does not require the use of oriented (or aligned) molecular beams or measurements of the orientation state of product molecules. Instead, it is shown that by numerically combining accurate measurements of the state-to-state differential cross section for two or more rotational states of the reagent molecule, the separate contribution from the individual helicity states can be extracted. New molecular beam experiments are conducted for the D+H2→HD+H reaction that confirm the validity of the method.
Bretislav Friedrich - One of the best experts on this subject based on the ideXlab platform.
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When diraction rules the Stereodynamics of rotationally inelastic collisions
The Journal of chemical physics, 2010Co-Authors: Mikhail Lemeshko, Pablo G. Jambrina, Marcelo P. De Miranda, Bretislav FriedrichAbstract:Following upon our recent work on vector correlations in the Ar-NO collisions [PCCP 12, 1038 (2010)], we compare model results with close-coupling calculations for a range of channels and collision energies for the He-NO system. The striking agreement between the model and exact polarization moments indicates that the Stereodynamics of rotationally inelastic atom-molecule collisions at thermal energies is governed by diffraction of matter waves from a two-dimensional repulsive core of the atom-molecule potential. Furthermore, the model polarization moments characterizing the He-NO, He-O$_2$, He-OH, and He-CaH Stereodynamics are found to coalesce into a single, distinctive pattern, which can serve as a "fingerprint" to identify diffraction-driven Stereodynamics in future work.
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communications when diffraction rules the Stereodynamics of rotationally inelastic collisions
Journal of Chemical Physics, 2010Co-Authors: Mikhail Lemeshko, Pablo G. Jambrina, Marcelo P. De Miranda, Bretislav FriedrichAbstract:Following upon our recent work on vector correlations in the Ar–NO collisions [Lemeshko and Friedrich, Phys. Chem. Chem. Phys. 12, 1038 (2010)], we compare model results with close-coupling calculations for a range of channels and collision energies for the He–NO system. The striking agreement between the model and exact polarization moments indicates that the Stereodynamics of rotationally inelastic atom-molecule collisions at thermal energies is governed by diffraction of matter waves from a two-dimensional repulsive core of the atom-molecule potential. Furthermore, the model polarization moments characterizing the He–NO, He–O2, He–OH, and He–CaH Stereodynamics are found to coalesce into a single, distinctive pattern, which can serve as a “fingerprint” to identify diffraction-driven Stereodynamics in future work.
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An analytic model of the Stereodynamics of rotationally inelastic molecular collisions
Physical chemistry chemical physics : PCCP, 2009Co-Authors: Mikhail Lemeshko, Bretislav FriedrichAbstract:We develop an analytic model of vector correlations in rotationally inelastic atom-diatom collisions and test it against the much examined Ar-NO (X(2)Pi) system. Based on the Fraunhofer scattering of matter waves, the model furnishes complex scattering amplitudes needed to evaluate the polarization moments characterizing the quantum Stereodynamics. The analytic polarization moments are found to be in an excellent agreement with experimental results and with close-coupling calculations available at thermal energies. The model reveals that the Stereodynamics is governed by diffraction from the repulsive core of the Ar-NO potential, which can be characterized by a single Legendre moment.
Marcelo P. De Miranda - One of the best experts on this subject based on the ideXlab platform.
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When diraction rules the Stereodynamics of rotationally inelastic collisions
The Journal of chemical physics, 2010Co-Authors: Mikhail Lemeshko, Pablo G. Jambrina, Marcelo P. De Miranda, Bretislav FriedrichAbstract:Following upon our recent work on vector correlations in the Ar-NO collisions [PCCP 12, 1038 (2010)], we compare model results with close-coupling calculations for a range of channels and collision energies for the He-NO system. The striking agreement between the model and exact polarization moments indicates that the Stereodynamics of rotationally inelastic atom-molecule collisions at thermal energies is governed by diffraction of matter waves from a two-dimensional repulsive core of the atom-molecule potential. Furthermore, the model polarization moments characterizing the He-NO, He-O$_2$, He-OH, and He-CaH Stereodynamics are found to coalesce into a single, distinctive pattern, which can serve as a "fingerprint" to identify diffraction-driven Stereodynamics in future work.
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communications when diffraction rules the Stereodynamics of rotationally inelastic collisions
Journal of Chemical Physics, 2010Co-Authors: Mikhail Lemeshko, Pablo G. Jambrina, Marcelo P. De Miranda, Bretislav FriedrichAbstract:Following upon our recent work on vector correlations in the Ar–NO collisions [Lemeshko and Friedrich, Phys. Chem. Chem. Phys. 12, 1038 (2010)], we compare model results with close-coupling calculations for a range of channels and collision energies for the He–NO system. The striking agreement between the model and exact polarization moments indicates that the Stereodynamics of rotationally inelastic atom-molecule collisions at thermal energies is governed by diffraction of matter waves from a two-dimensional repulsive core of the atom-molecule potential. Furthermore, the model polarization moments characterizing the He–NO, He–O2, He–OH, and He–CaH Stereodynamics are found to coalesce into a single, distinctive pattern, which can serve as a “fingerprint” to identify diffraction-driven Stereodynamics in future work.
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a unified quantal and classical description of the Stereodynamics of elementary chemical reactions state resolved k k j vector correlation for the h d2 v 0 j 0 reaction
Journal of Chemical Physics, 1999Co-Authors: Marcelo P. De Miranda, F J Aoiz, L Banares, Saez V RabanosAbstract:We present a detailed and quantitative comparison of the quantum mechanical (QM) and quasiclassical (QCT) descriptions of the Stereodynamics of elementary chemical reactions. Analogous formulations of the QM and QCT k–k′–j′ vector correlation in atom–diatom reactions have been derived and shown to be equivalent in the correspondence principle limit. The comparison between the results obtained from the application of the QM and QCT methodologies to the H+D2(v=0, j=0)→HD(v′,j′)+D reaction at a collision energy of 1.29 eV renders an almost quantitative agreement.
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using quantum rotational polarization moments to describe the Stereodynamics of the h d2 v 0 j 0 hd v j d reaction
Journal of Chemical Physics, 1998Co-Authors: Marcelo P. De Miranda, David C. Clary, Jesus F. Castillo, David E. ManolopoulosAbstract:We present results of quantum calculations we have performed on the title reaction in order to study its Stereodynamics at collision energies of 0.54 and 1.29 eV. Our theoretical model is based on a representation where directional properties are expressed in terms of real rotational polarization moments instead of magnetic quantum numbers. We analyze the physical meaning of rotational polarization moments and show that, when defined as in the present work, these quantities directly describe the reaction Stereodynamics in terms of intuitive chemical concepts related to preferences in the reaction mechanism for particular planes and senses of molecular rotation. Using this interpretation, we identify two distinct regimes for the Stereodynamics of the title reaction, observed when HD is formed with low or high rotational excitation. We also identify relevant characteristics of both regimes: (i) the existence and location of preferred planes and senses of molecular rotation, (ii) correlations between these p...
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Using quantum rotational polarization moments to describe the Stereodynamics of the H+D2(v=0,j=0)→HD(v′,j′)+D reaction
The Journal of Chemical Physics, 1998Co-Authors: Marcelo P. De Miranda, David C. Clary, Jesus F. Castillo, David E. ManolopoulosAbstract:We present results of quantum calculations we have performed on the title reaction in order to study its Stereodynamics at collision energies of 0.54 and 1.29 eV. Our theoretical model is based on a representation where directional properties are expressed in terms of real rotational polarization moments instead of magnetic quantum numbers. We analyze the physical meaning of rotational polarization moments and show that, when defined as in the present work, these quantities directly describe the reaction Stereodynamics in terms of intuitive chemical concepts related to preferences in the reaction mechanism for particular planes and senses of molecular rotation. Using this interpretation, we identify two distinct regimes for the Stereodynamics of the title reaction, observed when HD is formed with low or high rotational excitation. We also identify relevant characteristics of both regimes: (i) the existence and location of preferred planes and senses of molecular rotation, (ii) correlations between these p...