Interaction of Enantiomers

Catalytic Enantioselective Alkylation / 258 Diastereomeric Interaction of Enantiomers / 278 Effects on Solid-State Properties / 279 Effects in Solution / 281 References / 293... 

T. Williams et al., Diastereomeric solute-solute interactions of enantiomers in achiral solvents. Nonequivalence of the nuclear magnetic resonance spectra of racemic and optically active dihydroquinine. J. Am. Chem. Soc. 91, 1871-1872 (1969)... 

Millar, J.G., Giblin, M Barton, D., Morrison, A. and Underhill, E. W. (1990c). Synthesis and field testing of enantiomers of 6Z,9Z-d,v-3,4-epoxydienes as sex attractants for geometrid moths. Interactions of enantiomers and regioisomers.J. Chem. Ecol., 16, 2317-2339. 

In addition to the chiral interactions of enantiomers, interactions of dissimilar chiral species are fundamentally important. As described above, adenine becomes chiral upon adsorption and forms homochiral dimer chains on Cu(110). These chains are tilted 19.5° with respect to the [001] surface direction. This tilt makes the sites right next to an enantiomorphous supramolecular chain chiral Consequently, the interactions of inherently chiral molecules with both chain types are energetically nonequivalent. This... 

Fig. 6.5. Possible different interactions of enantiomers to the chiral cavity containing metalcoordinating sites obtained by molecular imprinting polymerisation.

HPLC suffers from certain drawbacks, as the chiral selectors are fixed on the stationary phase and hence no variation in the concentrations of the chiral selectors can be carried out. Moreover, a large amount of the costly solvent is consumed to establish the chiral resolution procedure. Additionally, the poor efficiency in HPLC is due to the profile of the laminar flow, mass transfer term, and possible additional interactions of enantiomers with the residual silanol groups of the stationary phase. Gas chromatography also suffers from certain drawbacks as discussed in the Introduction. ... 

Figure 2.12 Reprinted with permission from J. Am. Chem. Soc., vol. 91 T. Williams R. G. Pitcher P. Bommer J. Gutzwiller M. Uskokovic, Diastereomeric Solute-Solute Interactions of Enantiomers in Achiral Solvents. Nonequivalence of the Nuclear Magnetic Resonance Spectra of Racemic and Optically Active Dihydroquinine , pages 1871-1872 (1969). Copyright 1969, American Chemical Society.

Separation of enantiomers by nonchromatographic methods, such as catalysis or crystallization, is based on chemical transformation or phase transition. Both of these are "one-step" processes, while chromatography is a multistep separation method. This means that the overall resolution of the solutes originates from a large number of stereoselective one-step adsorption—desorption cycles. The cumulative nature of the chromatographic separation is the reason that a free energy difference in interactions of enantiomers with a chiral selector as small as 0.025 kj/mol may. 

The enantiomer separation by solid membranes may be classified into diffusion selective and sorption selective types. In the former type, the membrane without a specific chiral selector, but consisiting of chiral derived polymer is used, whereas in the latter one the membrane has the immobilized chiral selectors. With the use of diffusion selective membranes, the enantiomer separation is achieved through chiral environment within membrane, while with the sorption selective membranes the enantiomer separation proceeds by interaction of enantiomer with chiral selectors immobilized on the membrane. 

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