Optical Isomers in Solution Investigated by Nuclear Magnetic Resonance

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

doi:10.1070/rc1978v047n09abeh002277

Cited by 27 publications

(25 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Evidence of dimerization (i.e., the formation of homo‐ and heteroenantiomeric associates) has been provided through NMR diffusion measurements, as well as by analyzing the nonlinear behavior of optical rotation and UV absorbance as functions of the difference in the nominal concentration of the two enantiomers. Nonracemic mixtures of compounds such as amino alcohols, amides, and carboxylic acids, which strongly self‐associate, can exhibit anisochrony, and thus, reflect the enantiomer composition, even in the absence of lanthanide shift reagents …”

Section: Support For the Concept Of Dimeric Enantiomeric Associatessupporting

confidence: 60%

“…Horeau concluded that “certain effects observed by polarimeter, NMR, and calorimetry can only be explained when the existence of diastereomeric interactions of enantiomers in solution are taken into account.” Horeau and Guette, also reported difference in the PMR spectra of pure enantiomers and 1 : 1 (racemic) and 3 : 1 mixtures of α,α‐methylethyl‐ and α,α‐methylisopropylsuccinic acids in CDCl 3 and concluded that there occurred formation of diastereomeric associates of the enantiomers, of different stabilities, in solution. These studies were supported by Kabachnik et al . by NMR studies of nonracemic mixtures of the enantiomers (optical isomers) of N ‐[ S ‐(methylethoxyphosphinyl)‐thioglycolyl]valines, in solutions.…”

Section: Support For the Concept Of Dimeric Enantiomeric Associatesmentioning

confidence: 99%

See 1 more Smart Citation

Enantioseparations in Achiral Environments and Chromatographic Systems

Martens

Bhushan

2016

Israel Journal of Chemistry

View full text Add to dashboard Cite

Since the very first resolution of racemic tartaric acid by Pasteur, the importance of resolution and methodology has been on a path of continuous understanding and expansion. The science and chemistry of achieving such targets has changed a lot. The advent of chromatography changed the direction by involving synthetic, semisynthetic, or naturally occurring chiral materials for a direct approach to resolution, where rapid and reversible association occurs to form diastereomers with different stabilities and partition coefficients responsible for overall enantioseparation. It has now reached a stage where the separation of excess enantiomers from nonracemic mixtures has been achieved in a totally achiral environment, which does not appear to be in line with the prevalent concepts of basic stereochemistry. Caution should be exercised when enantiomerically enriched mixtures – obtained by enantioselective synthesis – are chromatographed for purification in preparative organic synthesis.

show abstract

Section: Support For the Concept Of Dimeric Enantiomeric Associatessupporting

confidence: 60%

Section: Support For the Concept Of Dimeric Enantiomeric Associatesmentioning

confidence: 99%

Enantioseparations in Achiral Environments and Chromatographic Systems

Martens

Bhushan

2016

Israel Journal of Chemistry

View full text Add to dashboard Cite

show abstract

“…therein). It is also known that nonracemic mixtures of enantiomers of compounds that strongly self-associate, e.g., amino alcohols, amides, and carboxylic acids, can exhibit anisochrony, thus reflecting the enantiomer composition even in the absence of shift reagents [19]. Association is often limited to the formation of dimers that may take place through the formation of H-bonds between enantiomers.…”

mentioning

confidence: 99%

Determination of the Dimerization Equilibrium Constants of Omeprazole and Pirkle's Alcohol through Optical‐Rotation Measurements

Baciocchi

Juza²,

Classen³

et al. 2004

Helvetica Chimica Acta

View full text Add to dashboard Cite

A new procedure to measure the equilibrium constants for the dimerization (homochiral and heterochiral) reactions of enantiomers in solution was applied to two different compounds, namely omeprazole and Pirkle×s alcohol, both in CHCl 3 . This procedure is based on the measurement of the optical rotation of the solution as a function of its composition, which exhibits a nonlinear dependence on the enantiomer enrichment. Such nonlinearity depends on the extent of dimerization, and it is a strong effect in the case of omeprazole, whose equilibrium constants are 14.0 AE 3.5 l/mol and 25.2 AE 4.0 l/mol for the formation of homochiral and of heterochiral dimers, respectively. Pirkle×s alcohol exhibits a weaker effect that allows only to estimate the order of magnitude of these constants, i.e., ca. 0.10 and 0.34 l/mol, respectively. Although, in solution, enantiomers and racemates of chiral compounds usually exhibit identical NMR spectra, small differences in the chemical shifts are sometimes observed (see [18] for an overview, as well as the ref. cit. therein). It is also known that nonracemic mixtures of enantiomers of compounds that strongly self-associate, e.g., amino alcohols, amides, and carboxylic acids, can exhibit anisochrony, thus reflecting the enantiomer composition even in the absence of shift reagents [19]. Association is often limited to the formation of dimers that may take place through the formation of H-bonds between enantiomers. This is the case for the enantiomers of the chiral [1,1'-binaphthalene]-2,2'-diol ( binaphthol) and 1-(anthracen-9-yl)-2,2,2-trifluoroethanol ( Pirkle×s alcohol). In the case of the enantiomers of binaphthol in CHCl 3 , we have recently been able, using an achiral chromatography column, to collect two fractions constituted of the pure enantiomer present in excess (reaching 100% e.e.) and of the racemic mixture, respectively [20]. In the case of Pirkle×s alcohol, the enantiomer enrichment of a nonracemic solution in hexane/CH 2 Cl 2 was also achieved through achiral chromatography on a silica stationary phase [12].

show abstract

“…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: 96%

Racemates revisited: heterochiral assemblies and the example ofdl-thalidomide

et al. 2011

View full text Add to dashboard Cite

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.

show abstract

Optical Isomers in Solution Investigated by Nuclear Magnetic Resonance

Cited by 27 publications

References 0 publications

Enantioseparations in Achiral Environments and Chromatographic Systems

Enantioseparations in Achiral Environments and Chromatographic Systems

Determination of the Dimerization Equilibrium Constants of Omeprazole and Pirkle's Alcohol through Optical‐Rotation Measurements

Racemates revisited: heterochiral assemblies and the example ofdl-thalidomide

Contact Info

Product

Resources

About