An NMR study of optical isomers in solution

Кабачник, М. И.; Mastryukova, T. A.; Fedin, É. I.; Vaisberg, M. S.; Morozov, L. L.; Petrovsky, P. V.; Шипов, А. Г.

doi:10.1016/0040-4020(76)85164-2

Cited by 56 publications

(24 citation statements)

References 11 publications

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“…1-12), plus two mass balance equations (Eqs. [13][14] are available, the system is fully described. Unfortunately, the different parameters included in this model such as stability constants (Eqs.…”

Section: ) Complete Theoretical Modelmentioning

confidence: 99%

Enantiomeric enrichment of non-racemic mixtures of binaphthol with non-chiral packings

Nicoud¹,

Jaubert²,

Rupprecht³

et al. 1996

Chirality

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Section: ) Complete Theoretical Modelmentioning

confidence: 99%

Enantiomeric enrichment of non-racemic mixtures of binaphthol with non-chiral packings

Nicoud¹,

Jaubert²,

Rupprecht³

et al. 1996

Chirality

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“…Similarly, substituted derivatives of the amino acid, valine, have been shown to undergo associate diastereisomerism when in solution (Kabachnik et al, 1976(Kabachnik et al, , 1978 as have various phosphinothioic acids and amides (Harger, 1976(Harger, , 1977(Harger, , 1978a and phenyl sulphoxides (Pirkle and Hoover, 1982). Also, the two enantiomers of urea derivatives of α-phenylethylamine have been shown to interact in solution to form dimeric racemic assemblies, stabilized by hydrogen bonding across the urea fragments (Huang et al, 2009).…”

Section: Commentarymentioning

confidence: 97%

Racemates revisited: heterochiral assemblies and the example ofdl-thalidomide

et al. 2011

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The existence of racemic compounds, comprised of pairs of opposite enantiomers as discrete molecular entities, has been accepted for over a century. However, their ability to remain as associated dimers when in solution is uncertain, if not generally doubted. In this article, data has been assembled to provide evidence for the presence of intact dimeric heterochiral assemblies in solution and presents DL-thalidomide as a probable example of this phenomenon.

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“…Previous reports have revealed that a mixture of enantiomers occasionally exhibits unusual physical and chemical properties attributable to the formation of diastereomeric species in solutions 22–23. A racemic chiral compound had a 1 H NMR spectrum that significantly differed from that obtained for the individual enantiomers 24–26. The solubility of the racemic compound, as opposed to that of its enantiomer, might result in the ability of the racemic phosphoric acid to form an aggregate which is a more energetically preferable diastereomeric species compared to that obtained from the optically pure enantiomer and is more difficult to dissociate in a nonpolar solvent.…”

Section: The Ee Values Of the Solution And Precipitated Solid Measurementioning

confidence: 98%

Asymmetric Amplification in Phosphoric Acid Catalyzed Reactions

Chen

Zhou

et al. 2010

Angewandte Chemie

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Methodologies involving chiral resolution, chiral auxiliary induced transformations, and asymmetric catalytic reactions, including those catalyzed by metal, biological, and organic catalysts, have been developed and, typically, these processes have exploited optically pure catalysts to ensure high enantioselectivity. In these reactions, the enantiomeric excess (ee) of the reaction product was linearly proportional to the ee value of the chiral catalyst or auxiliary. However, chemists have observed numerous exceptions to this linear relationship, some characterized by a positive nonlinear correlation between the ee value of the reaction product and that of the chiral catalyst or auxiliary. [1][2][3][4][5][6][7] This phenomenon, termed asymmetric amplification, has not only provided cost effective asymmetric synthetic protocols in comparison with those using enantiomerically pure catalysts, but has also been considered a basis for the origin of homochirality in nature. [8][9] In the last decades, metal-based asymmetric amplified catalysis has undergone great advances.[6] Recent applications of asymmetric amplification in organocatalysis, particularly the use of biologically relevant molecules such as amino acids as catalysts, have advanced the long standing inquiry into the evolution of homochirality in the prebiotic system. [10][11][12][13] However, the importance of asymmetric amplification in reactions catalyzed by phosphoric acids and its derivatives, [14][15][16][17][18] an important class of pentavalent phosphorus compounds relevant to nucleic acids, has been less recognized. [19] During our studies on the phosphoric acid catalyzed Biginelli reaction, [20] we found a strong positive nonlinear effect (NLE) for the reaction of para-nitrobenzaldehyde (2), thiourea (3), and ethyl acetoacetate (4) in the presence of 10 mol % of the non-enantiopure 3,3'-ditriphenylsilyl binolderived phosphoric acid 1 a in toluene (Figure 1 a).[21] In contrast, an absolutely linear effect was observed for the same reaction under almost identical reaction conditions except that chloroform was used as the reaction medium instead of toluene (Figure 1 b). Kinetic studies revealed that the optically pure phosphoric acid afforded a much faster reaction in toluene (Figure 1 c), but in chloroform, the optically pure and the racemic catalysts exhibited comparable catalytic activities (Figure 1 d). Similarly, electron-rich benzaldehydes also participated in the reaction to show similar positive NLE as exemplified by 2-methylbenzaldehyde (see the Supporting Information). The strong dependence of the NLE upon the solvent prompted us to investigate this observation in detail. In proline-catalyzed reactions, the nature of the solvent played a distinct role in the NLE, and this role was attributed to the solubility differences between racemic and optically pure samples. [12][13] In the phosphoric acid catalyzed Biginelli reaction, we speculated that the significant dependence of the asymmetric amplification upon the solvent is also Figure 1. Asymm...

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An NMR study of optical isomers in solution

Cited by 56 publications

References 11 publications

Enantiomeric enrichment of non-racemic mixtures of binaphthol with non-chiral packings

Enantiomeric enrichment of non-racemic mixtures of binaphthol with non-chiral packings

Racemates revisited: heterochiral assemblies and the example ofdl-thalidomide

Asymmetric Amplification in Phosphoric Acid Catalyzed Reactions

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