Results 251 to 260 of about 691,764 (293)

Frozen Solution-Mediated Asymmetric Synthesis: Control of Enantiomeric Excess

The Journal of Organic Chemistry, 2020
Asymmetric List-Mannich reactions were carried out in the frozen state to afford optically active adducts in moderate-to-good chemical yields and enantiomeric excesses (ee). The frozen solution exerts critical control of ee via entropy changes, in sharp contrast to the enthalpy-driven asymmetric reactions typically observed in homogeneous solvents ...
Koki Iijima, Makoto Harada, Gaku Fukuhara, Tetsuo Okada   +3 more
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Enantiomeric Excess of Amino Acids in Hydrothermal Environments

Origins of Life and Evolution of Biospheres, 2005
In a simulated hydrothermal environment allowing fluid circulation between hot and cold regions repeatedly, D- and L-alanine molecules were racemized differently depending upon the concentration of alanine, whether D or L, present in the solution. In particular, the relative population of L-alanine was slightly more enhanced compared to that of D ...
Atsushi, Nemoto, Minako, Horie, Ei-Ichi, Imai, Hajime, Honda, Kuniyuki, Hatori, Koichiro, Matsuno   +5 more
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Determination of enantiomeric excess by chiral liquid chromatography without enantiomerically pure starting standards

Biomedical Chromatography, 2012
ABSTRACTA facile approach for the enantiomeric excess determination of enantiomeric mixtures without the necessity of pure enantiomer standards is presented. Promethazine and trimeprazine commercial nonracemic mixtures were used as cases study to probe the validity of the method.
F G, Sánchez, A, Navas Díaz, E, Sánchez Torreño, A, Aguilar, I, Medina Lama, M, Algarra   +5 more
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Asymmetric Synthesis. Kinetic Amplification of Enantiomeric Excess

Comments on Inorganic Chemistry, 1987
Abstract The efficiency of an asymmetric synthetic reaction is measured by what is called the enantiomeric excess (e.e.). It is commonly assumed that this is a unique quantity for a given asymmetric reaction under specified conditions. The purpose of this Comment is to show that this is not necessxily so, and that, under certain circumstances, e.e.
Steven Bergens, B. Bosnich
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ChemInform Abstract: Rapid Enantiomeric Excess Determination

ChemInform, 2013
AbstractReview: 29 refs.
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Recent Advances in the Measurement of Enantiomeric Excesses

Advanced Synthesis & Catalysis, 2002
The elaboration of an ever increasing number of chiral catalysts or reagents demands fast and sensitive methods to measure enantiomeric excesses of the products. This review discusses the various ways to solve these problems. Mass spectrom- etry, chromatographic or chiroptical methodologies, fluorescence, liquid crystals, enzymatic methods, and ...
Masaki Tsukamoto, Henri B. Kagan
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Rapid determination of enantiomeric excess: a focus on optical approaches.

Chem. Soc. Rev., 2012
High-throughput screening (HTS) methods are becoming increasingly essential in discovering chiral catalysts or auxiliaries for asymmetric transformations due to the advent of parallel synthesis and combinatorial chemistry. Both parallel synthesis and combinatorial chemistry can lead to the exploration of a range of structural candidates and reaction ...
Diana Leung, S. Kang, E. Anslyn
semanticscholar   +3 more sources

Rapid Determination of Enantiomeric Excess Using Infrared Thermography

Organic Process Research & Development, 2002
Infrared thermography (IRT) is presented as a novel technique to screen a potentially large number of asymmetric catalysts or substrates in a high-throughput fashion.
Nicolas Millot, Phil Borman, Mike S. Anson, Ian B. Campbell, Simon J. F. Macdonald, Mahmoud Mahmoudian   +5 more
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Determination of enantiomeric excess using Raman optical activity

Journal of Raman Spectroscopy, 1995
AbstractA simple method for the determination of enantiomeric excess is described. It is based on depolarized Raman optical activity (ROA) measurements in right‐angle scattering employing the incident ciruclar polarization (ICP) modulation approach. The accuracy of this method was assessed utilizing α‐pinene as a chiral test compound. The four α‐pinene
Lutz Hecht, Anthony L. Phillips, Laurence D. Barron   +2 more
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Direct 1H NMR determination of the enantiomeric excess of carnitine

The Analyst, 1988
The enantiomeric purity of carnitine may be determined without any derivatisation of the molecule. Preparations of aqueous mixtures containing stereochemically pure L-malic acid, carnitine and europium trichloride lead to the formation of a complex in which the trimethylammonium groups of D- and L-carnitine are diastereotopic.
J, Bounoure, J, Souppe
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