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Solvents optically active

In general, it may be said that enantiomers have identical properties in a symmetrical environment, but their properties may differ in an unsymmetrical environment. Besides the important differences previously noted, enantiomers may react at different rates with achiral molecules if an optically active catalyst is present they may have different solubilities in an optically active solvent., they may have different indexes of refraction or absorption spectra when examined with circularly polarized light, and so on. In most cases these differences are too small to be useful and are often too small to be measured. [Pg.126]

Optically active oxaziridines are useful reagents for the enantioselective oxidation of olefins 37 39). The following three preparative methods to make this reagent available have been reported enantioselective oxidation of an imine by (-)-peroxycam-phoric acid 37,38), photocyclization of a nitrone which has a chiral substituent39), and photocyclization of a nitrone in an optically active solvent 39). However, an... [Pg.237]

After quenching with DzO or Bu OD, analysis of the products from the Grignard reagents formed from PhCHXMe (X = Cl, Br, I) in the optically active solvent -(R)-2-methoxypentane leads to the conclusion that Grignard reagent formation occurs on the Mg surface within a solvent cage by a one-electron transfer mechanism.1... [Pg.84]

Recently, the first example of chiral solvation of a polysilane was demonstrated dissolution of the inherently optically inactive poly(methylphenylsilyene), PMPS, and poly(hexylmethylsilylene), PHMS, in the optically active solvents (V)-2-methyl-l-propoxybutane and (V)-(2-methylbutoxymethyl)benzene induced the polymer chains to adopt PSS helical conformations as evidenced by (positive-signed) Cotton effects almost coincident with the UV a-a transition at 340 and 305 nm, respectively.332... [Pg.622]

Dimethyl isosorbide (VI) has been prepared in quantitative yield from isosorbide and dimethyl sulphate according to known procedure (1). It is a liquid possessing a low vapor pressure at room temperature and boiling point of 95°C at 0.1 mm Hg. In addition, it also possesses optical activity. It is expected to be a relatively inexpensive solvent (for an optical active solvent with 100% purity of the optical isomer) in comparison to... [Pg.180]

CN or A, led to no measurable resolution. When heated in an optically active solvent, (-)-2-methyl-l-butanol, recovered BN remained racemic. On the other extreme, irradiation of crystals of optically active BN at room temperature produced no measureable racemization. When recrystallized very slowly at room temperature from (-)-2-methyl-l-butanol, BN displayed no measureable optical activity. [Pg.155]

Finally, an interesting application of chiral solvents in the determination of the optical purity and the absolute configuration of solutes by NMR spectroscopy should be mentioned. Experimental observations indicate that the NMR spectra of enantiomeric mixtures in certain optically active solvents show small splittings of some of the peaks cf. Table A-2 in the Appendix for chiral solvents). For example, Pirkle et al. [284] have examined the and F NMR spectra of enantiomeric 2,2,2-trifiuoro-l-phenylethanol in optically active l-(l-naphthyl)ethylamine. In the chiral solvent, the solute gives rise to distinct signals for each enantiomer. These observations are explained as the result of... [Pg.386]

W. H. Pirkle, The nonequivalence of physical properties of enantiomers in Optically active solvents. Differences in nuclear magnetic resonance spectra. I, /. Am. Chem. Soc. 88 (1966), 1837. [Pg.1046]

Mustillo and CiurczakP" presented a paper discussing the spectral effect of optically active solvents on enantiomer mixes. This information was used as a technique to screen for polar modifiers in normal-phase chromatography of racemic mixtures. In 2000, the enantiomeric composition of ibuprofen in solid-state mixtures was performed by Agatonovic-Kurstrin, Beresford, Razzak. ... [Pg.3436]

Figure 10. CD spectra of poly(n-hexylisocyanate) (poly-85) dissolved in optically active solvents at 20 °C. Ultraviolet spectrum (bottom) shown only for (A)-2-chlorobutane (polymer concentration 1.9 mg/mL). (Reprinted with permission from ref 171. Copyright 1993 American Chemical Society.)... Figure 10. CD spectra of poly(n-hexylisocyanate) (poly-85) dissolved in optically active solvents at 20 °C. Ultraviolet spectrum (bottom) shown only for (A)-2-chlorobutane (polymer concentration 1.9 mg/mL). (Reprinted with permission from ref 171. Copyright 1993 American Chemical Society.)...
A new aliphatic helical topology was realized with the synthesis of the first molecular Mobius-band molecule 89, which was obtained in 57 % yield from 90. The chirality of 89 was proved by the NMR method using (+)-(2,2,2)-trifluoro-9-anthrylethanol as an optically active solvent... [Pg.32]

A new n.m.r. shift reagent, tris-[3-(t-butylhydroxymethylene)-d-camphorato]-europium(m), should prove to be useful for the determination of enantiomeric purity of chiral / -phen ethyl amines.2 For example, it was found that the CHNH2 resonances of (R)- and (S)-amphetamines were separated by 0.7 p.p.m. in a carbon tetrachloride solution of the europium reagent ( 0.15 mol 1 l. In comparison to the use of optically active solvents for the same purpose, this technique has the advantage of showing very large shifts between resonances of enantiomers. Mass spectrometry has been used in the detection of mescaline and tetrahydro-isoquinoline precursors as biochemical intermediates.3 Spectral differences of 4-chloro-2-nitrobenzenesulphonyl derivatives of ephedrine and related compounds have been used for identification purposes.4... [Pg.97]

A special type of chemical shift non-equivalence arises when a racemic mixture is dissolved in an optically active solvent. Solvent-solute interactions would be expected to be different for the enantiomers and should show up as non-equivalence of corresponding nuclei in the two forms. The effects so far detected,are disappointingly... [Pg.9]

Figure 6 shows the methine resonance (100 Me./sec.) and the trifluoromethyl resonance (941 Mc./sec.) in (a) racemic and (b) optically active a-(l-naphthyl)ethylamine. In the optically active solvent, the solute gives rise to distinct signals for each enantiomer. [Pg.117]

A second approach to Isomer separation by HPLC Is to use a non-optlcally active stationary phase and an optically active solvent. If the amino acids can Interact with both the stationary and mobile phases, but one of the Isomers Interacts more strongly with the mobile, optically active phase, separation of the Isomers Is possible (49). In 1979, several laboratories reported methods Involving the use of chiral mobile-phases containing zlnc(II) or copper (II) complexed to an L-amlno acid (51-53). A distinct advantage of these methods Is that they do not require derlvatlza-tlon of the sample prior to analysis. However, separation of a complete mixture of amino acids (such as that obtained from a protein hydrolysate) has not been reported. [Pg.173]

A recent interesting application of solvent effects has been the use of optically-active solvents in the determination of the optical purity and the absolute configuration of solutes. Work so far has centred on resonances and organic solutes, covering various alcohols, amines, sulphoxides, a-hydroxy- and a-amino-acids, and epoxides (the solvent here being an optically active nematic phase ). There are also reports on disymmetric nickel(II) complexes, and the use of resonances. ... [Pg.515]

The experimental observations are that the spectra of enantiomeric mixtures in certain optically-active solvents, either pure, or diluted with an optically-inactive solvent, show small splittings of some of the peaks. The separations may be up to 8 Hz (measured at 100 MHz) but are typically about one-third of this value. A typical solvent is (—) 2,2,2,-trifiuorophenylethanol, but the requirements of a suitable solvent have not been fully delineated. [Pg.515]

More recent work ° shows a very specific coordination role for such solvents as dimethylformamide, dimethylacetamide and dimethyl-sulphoxide in the catalysis of hydrogenation reactions by rhodium(III) complexes such as [RhCl3(py)3]. Particularly interesting are the results in (-f) or (—)-l-phenylethylformamide, where through simultaneous coordination to the rhodium with the substrate methyl-3-phenylbut-2-en-oate, the optically active solvent encourages stereospecific hydrogenation to yield (+) or (—)-methyl 3-phenylbutanoate. These results emphasise that further kinetic studies in optically active solvents would be interesting (see p. 717). [Pg.724]

The differing effects of hydrogen ion or of base concentration on thiocyanate substitution rates into rans-[CoCl2 enal and into trans-[CoCl(N02)en2]+ in methanol or ethanol support an earlier hypothesis that the mechanisms are not identical for these two complexes, but that there is considerable solvent assistance in the case of the chloronitro-compound. However, one should recall an earlier study in mixed aqueous alcoholic solvents which indicated no diflFerence in substitution mechanisms for these two complexes. Chloride and thiocyanate substitution at cis-[CoCl2diars]+ in methanol both involve formation of the same inter-mediate. Solvolysis of optical and geometrical isomers of [CoCl2en2]+ in an optically active solvent, propane-1,2-diol, results in stereospecific substitution. ... [Pg.164]

The first enantiomeric separation was credited to Louis Pasteur, who in 1848 manually sorted crystals of sodium ammonium tartrate based on their different crystalline appearances. Advances in technology and separation science have been paralleled by similar advances in enantiomeric separation methods. These have included preferential crystallization, crystallization from optically active solvents, fractional crystallization of diaslereo-... [Pg.215]


See other pages where Solvents optically active is mentioned: [Pg.76]    [Pg.203]    [Pg.27]    [Pg.28]    [Pg.313]    [Pg.69]    [Pg.230]    [Pg.100]    [Pg.15]    [Pg.230]    [Pg.203]    [Pg.145]    [Pg.10]    [Pg.117]    [Pg.598]    [Pg.218]    [Pg.497]    [Pg.515]    [Pg.717]    [Pg.138]    [Pg.68]    [Pg.654]   
See also in sourсe #XX -- [ Pg.100 ]




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