Isomerization solutions

Figure A3.8.1 A schematic diagram of the PMF along the reaction coordinate for an isomerizing solute in the gas phase (frill curve) and in solution (broken curve). Note the modification of the barrier height, the well positions, and the reaction free energy due to the interaction with the solvent.

In some cases where bridged dianhydrides were used, four signals were observed in NMP, evidently because of the ability to transfer K-electron density through such bonds as ether, sulfone, or ketone as discussed above. As an example of such behavior, the diamic acid isomeric solution based on l,l -bis(3,4-carboxyphenyl)sulfone dianhydride (SDA) displayed the spectrum illustrated in... 

Depolarized Raman spectra below 250 cm" in liquid water (H2O, D2O and H2 0), aqueous electrolyte solutions (LiCl, NaCl, KCl, RbCl, MgCl2 and CaCl2), D-glucose solution and ascOTbic acid isomerism solutions (L-xylo and D-arabo) were investigated. The Raman spectra... 

Fig.6 shows the concentration dependence of the damping constants in the ascorbic acid isomerism solutions. We can see that the change of the damping constant g2 in D-arabo ascorbic acid is more drastic than that in L-xylo ascorbic acid. ... 

Isomeric solutes that have closely related structure with slight difference in v.p. and degree of interaction with conventional stationary phases provide difficult separation problems. Liquid crystal, N,N -bis(p-methoxybenzylidene)-a,o -bi-p-toluldine, was used for separation of several PAH, in general, and benzo (a) pyrane and benzo (e) pyrene in particular (27). 

Fig. 5.5. Partial Ag+-HPLC chromatograms with a relative retention volume (RRV) scale, of the iodine-isomerized solutions containing each CLA positional isomer from 6,8- to 13,15-18 2 as FAME. A small quantity of c9,fl 1-18 2 was co-injected with each positional mixture for reference. Chromatographic conditions three ChromSpher 5 Lipids columns in series at 25°C, 0.1% MeCN/0.5% DE/hexane mobile phase at 1.0 mL/min, UV detection at 233 nm.

Chromatograms obtained using these conditions are shown in Fig. 5.7. The set of the iodine isomerized solutions containing all the positional isomer from 6,8- to 13,15-18 2 are presented. Under these operating conditions there is no appreciable drift in retention times, and so it was not necessary to obtain relative retention volumes... 

Two geometrically isomeric solutes were easily separated maleate (cis form) and fumarate (trans form). The hydrophobic or hydrophilic nature of a soluble strongly affects the retention time in this system. Thus, the polar effects of the two carboxyl groups gave phthalate a shorter retention time than benzoate, which has a single carboxyl group. In conventional IC, the 2- phthalate anion would be... 

HFCLM-based Isomer Separation Processes. Armstrong and Jin (33) studied liquid membrane permeation through an aqueous SLM in a cellulose filter placed in a batch cell. The feed consisted of a 50-50 mixture of organic isomeric solute systems (structural, stereoisomers, etc.) in an organic solvent with the same solvent present in the permeate side. They incorporated p-cyclodextrin (they also tested a-and y-) in the aqueous solution to develop selectivity for one isomer over the other. Considerable selectivity was achieved initially. With time the selectivity was lost due to the inherent nature of the batch system. 

Table 5. Examples of isomeric solutes separated using monomeric and polymeric liquid crystalline stationary phases.

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