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Chiral interaction shifts

The Pfeiffer effect is a term used to describe changes in the optical activity of solutions containing a chiral compound (the environmental substance ) on the addition of a racemic dissymmetric complex. The effect is generally attributed to a shift in the position of the equilibrium between d and l isomers for the racemic complex. The exact mechanism involved in mediating the chiral interaction is unknown. Perhaps surprisingly, both environmental substance and complex may simultaneously be cations. Studies of the Pfeiffer effect usually involve a moderately labile racemic complex [Cr(ox)3]3 is a popular choice for such studies, summarized in Table 82. Other studies of the optical activity of tris oxalates include work on photoinduced optical activity,898 photoracemization899 and the solid-state racemization of K3[Cr(ox)3]. 900 901... [Pg.871]

Its extension to heavy baryon chiral perturbation theory (HBCHPT) [3] allows to calculate many of the experimentally accessible processes in the meson nucleon sector. The check of the soundness of this approach requires high precision experiments. This resembles the situation in the development of QED during the last 50 years, where the measurement of the Lamb shift contributed much to the development of QED. In a comparable way the measurement of strong interaction shift and width in pionic hydrogen may be a key experiment in strong interaction physics at low energies. [Pg.509]

Chiral lanthanide shift reagents (LSR) also promote asymmetric hetero Diels-Alder reactions (Figure 45) 131-134 Lack of rigorous structural information regarding LSR/carbonyl interactions, however, does not allow meaningful speculation on the source of chirality transfer. [Pg.314]

NMR, the most powerful of the spectroscopies, can be used to identify enantiomer ratios. Firstly, these enantiomers have either to interact or combine with one enantiomer of a suitable compound so that the NMR spectrometer can perceive the resultant diastereomeric complexes or diastereoisomers as separate signals. The suitable compounds can be a chiral solvent, a chiral lanthanide shift reagent or, for an alcohol, an ester made from a chiral acid in each case the chiral agent must be enantiomerically pure. Integration of observed separate signals... [Pg.157]

Resolved Troger s base (1) interacts with chiral alcohols as a chiral NMR shift reagent.It is also possible to use enantiopure Troger s bases for chiral resolution and chiral induction. When 1 X=H) was imprinted... [Pg.1520]

Fluorescence is a spectroscopic technique which has been widely used to study molecular interactions, particularly in biological systems [103], It is also a useful tool for the study of chiral interaction and discrimination. It can provide useful information about molecular interactions with a high sensitivity. The application of fluorescence to specifically study enantioselective interactions and chiral recognition has been reported [104-113]. Most of these fluorescence studies involve the measurements of fluorescence emission intensities, spectral shifts, and quenching effects. [Pg.316]

The first is observed when the chiral solvating agent has a high association with the achiral lanthanide complex. Bonding of the CSA to the lanthanide (Ln) effectively creates a chiral lanthanide shift reagent (Ln-CSA) (Eqn [4]). This species then interacts... [Pg.420]

Yanagihara R, Tominaga M, Aoyama Y. Chiral host-guest interaction. A water-soluble calix[4]resorcarene having L-proline moieties as a non-lanthanide chiral NMR shift reagent for chiral aromatic guests in water. J. Org. Chem. 1994 59 6865-6867. [Pg.1527]

Chiral organoselenenyl halides may also be stabilized by intramolecular Se N interactions Se NMR chemical shifts indicate that these interactions are maintained in solution. ... [Pg.306]

As already mentioned, chiral cations are involved in many areas of chemistry and, unfortunately, only few simple methods are available to determine their optical purity with precision. In the last decades, NMR has evolved as one of the methods of choice for the measurement of the enantiomeric purity of chiral species [ 110,111 ]. Anionic substances have an advantage over neutral reagents to behave as NMR chiral shift agents for chiral cations. They can form dia-stereomeric contact pairs directly and the short-range interactions that result can lead to clear differences in the NMR spectra of the diastereomeric salts. [Pg.34]

Results of liquid phase NMR measurements (Table 4) show that only the real substrates influences the proton shift of H3 and H9 protons of CD. These data confirmed the liquid phase interaction between the diketones and the chiral modifier. No effect of dummy substrates (ethyl acetate, acetone, etc.) was observed. No direct connection was found between kinetic data (reaction rate and optical yield) and NMR proton shift. Liquid phase NMR measurements confirmed the interaction of both 2,3-butandione and 3,4-hexanedione with the alkaloid used. [Pg.545]


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See also in sourсe #XX -- [ Pg.80 ]




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Interaction chiral

Shift chiral

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