CHIRAL MEDIA

For a source-free, isotropic, chiral medium, the Maxwell equations are given by (1.10), with the K matrix defined by (1.11). Following Bohren [16], the electromagnetic field is transformed to 

The transformed fields L and R are the left- and right-handed circularly polarized waves, or simply the waves of left- and right-handed t3q)es. Explicitly, the electromagnetic field transformation is 

For chiral media, we use the same technique as for anisotropic media and express the left- and right-handed circularly polarized waves as integrals over plane waves. For the Fourier transform corresponding to waves of left-handed type, 

For the waves of right-handed type we proceed analogously. We obtain the integral representation 

In conclusion, the electric and magnetic fields propagating in isotropic, chiral media possess the expansions [16,17,135] 

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NMR spectra of oxaziridine enantiomers may be different from each other in chiral media. In the presence of chiral arylperfluoroalkylcarbinols, shift differences of up to 0.35 p.p.m. are observed, which may be used for discrimination of enantiomers (77JOC3217). 

Ward, T. J., Chiral media for capillary electrophoresis, Anal. Chem., 66, 634A, 1994. 

XVII. Beltrami Field Relations from Time-Harmonic EM in Chiral Media... 

XVII. BELTRAMI FIELD RELATIONS FROM TIME-HARMONIC EM IN CHIRAL MEDIA... 

Besides its appearance in the FFMF equation in plasma physics, as well as associated with time-harmonic fields in chiral media, the chiral Beltrami vector field reveals itself in theoretical models for classical transverse electromagnetic (TEM) waves. Specifically, the existence of a general class of TEM waves has been advanced in which the electric and magnetic field vectors are parallel [59]. Interestingly, it was found that for one representation of this wave type, the magnetic vector potential (A) satisfies a Beltrami equation ... 

A. Lakhtakia et al., Time-Harmonic Electromagnetic Fields in Chiral Media, Springer-Verlag, Berlin, 1989. 

Liquid-Crystalline Solvents as Mechanistic Probes The Properties of Ordered Chiral Media That Influence Thermal and Photochemical Atropisomeric Interconversions of l,l -Binaphthyl... 

The photoresolution of JIN proceeds most efficiently In chiral media without singlet quenchers and with macroscopic order. Several factors may contribute to the necessity of long-range order. One of these Is the ability of cholesteric media to... 

Since nuclear magnetic resonance is a scalar probe, enantiotopic nuclei are isochronous (i.e. have the same chemical shift) in achiral media. Such nuclei, however, become diastereotopic in chiral media and thus, in principle (though often not in practice) anisochronous. Among many examples 26,27) are the enantiotopic methyl protons of dimethyl sulfoxide, CH3SOCH3, which are shifted with respect to each other by 0.02 ppm 26c) in solvent QH5CHOHCF3. (Surprisingly the 13C signals of the... 

Upon irradiation of alkene 103 in a dye-exchanged zeolite Na-Y in the presence of a chiral media [(+)-ephedrin] and molecular oxygen, a small enantioselectiv-ity of 15% enantiomeric excess (ee) was found. This first experiment of an asymmetric ene photo-oxygenation reaction within the zeolite cavity is interesting, promising, and merits further investigation. 

CHIRAL MEDIA FOR ASYMMETRIC SOLVENT INDUCTIONS. (S,S)-(+)-l,4-BIS(DIMETHYLAMINO)-2,3-DIMETHOXYBUTANE FROM (R,R)-(+)-TARTARIC ACID DIETHYL ESTER... 

A wide variety of substituted y-butyrolactones can be prepared directly from olefins and aliphatic carboxylic acids by treatment with manganic acetate. This procedure is illustrated in the preparation of 7-( -OCTYL)-y-BUTYROLACTONE. Methods for the synthesis of chiral molecules are presently the target of intensive investigation. One such general method developed recently is the employment of certain chiral solvents as auxiliary agents in asymmetric synthesis. The preparation of (S.SM+H, 4-BIS(DIMETHYLAMINO)-2,3-DIMETHOXY-BUTANE FROM TARTARIC ACID DIETHYL ESTER provides a detailed procedure for the production of this useful chiral media an example of its utility in the synthesis of (+)-(/ )-l-PHENYL-l-PEN-TANOL from benzaldehyde and butyllithium is provided. 

Some examples of enantioselective syntheses, carried out in chiral media, have already been given at the end of Section 3.2, which deals with chiral solvents cf. also Table A-2 (Appendix). In general, asymmetric inductions as a result of chiral solvents or chiral cosolvents are disappointingly low [700], The reason for this is that the differential solvation by the chiral solvent of the two enantiomorphic activated complexes which lead to either the (/ )- or (S)-product is not sufficient. That is, the difference in Gibbs energy of activation, AAG = AG — AG -, is not large enough to favour only one of the two enantiomeric products. It should be remembered that a difference of AAG = 10.8 kJ/mol (2.6 kcal/mol) at 20 °C would be sufficient to get an product ratio of 99 1 i.e. an enantiomeric excess ee = 98%). 

Recent efforts have focused also on the possible realization of enantioselective reactions. The use of organized chiral media has met with some success. Benzonorbomadiene forms stoichiometric complexes... 

The development of enantioselective chemical processes is critical to the preparation of enantiomerically pure bioactive compounds. Roughly 75% of small molecule pharmaceuticals are marketed in enantiomerically pure form [1], Enantioselective chemical processes require the use of chiral media that drive chemical reactions kinetically to produce one of two enantiomers selectively. Many such enantioselective... 

Enantiotopic nuclei or groups are capable of fulfilling all or, at least, most of the foregoing symmetry-related expectations. Their chemical shifts depend, in addition, on both the medium in which the NMR experiment is conducted and the spectral resolution of the spectrometer. The latter is influenced by, for example, the magnetic-field strength. Enantiotopic groups are isochronous in achiral or racemic media and constitute A2,X2, etc., systems. Moreover, they are potentially anisochronous in chiral media. 

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