Enantiomer purity

Similarly, a number of other electrophiles were tested, and the results are shown in Scheme 14. In all cases, the products of alkylation were formed in excellent yields. Comparison of the absolute configuration and enantiomer purity of the various products with that of the stannane reveal that the trends observed in the A-methyl series (Scheme 9) are largely followed carbon dioxide adds with retention of configuration, while most primary... 

The most convenient and most popular analytical methodology to assess enantiomer purity is the direct separation of enantiomers on so-called chiral stationary phases (CSPs). CSPs consist of an (ideally) inert chromatographic support matrix incorporating chemically or physically immobilized SO species. CSPs may be created by a variety of SO immobilization techniques, including (i) covalent attachment onto fhe surface of suitably pre-functionalized carrier materials, (ii) physical fixation employing coating techniques, and (iii) incorporation into polymeric networks by copolymerization, or combinations of these procedures. 

Enantiomer purity A description of the enantiomer composition of a sample, historically expressed as % ee. Because this term implies that the impurity is the racemate (not the minor enantiomer), many authors prefer to use enantiomer ratio, er, normalized to 100%. 

Enantiomer ratio, er The ratio of two enantiomers. When used as an expression of enantiomer purity, this ratio is often normalized to 100% i.e., 99 1, 80 20). 

As it was already discussed in the above cases, enantiomeric enrichment of racemate forming enantiomeric mixtures result in an almost racemic crystalline phase when the starting enantiomer purity is smaller than the eutectic composition (eeo < eCeu), but highly enriched mixture or the sole enantiomer can be crystallized when the initial composition is bigger than the eutectic one (eeo > cCeu)... 

Application of TLC to determine the enantiomer purity via separation of diastereomeric derivatives is a relatively straightforward, though seemingly little used, technique. One example is the analysis of a nonracemic carboxylic acid synthetic intermediate as the amide formed with l-(a -naphthyl)ethylamine (Reference [11] and references therein). 

TLC plates coated with chiral ligand-exchange media have been applied to the analysis of amino acid mixture, as such (Reference [11] and literature therein) or either after derivatization [59]. The plates coated with /3-cyclodextrin have been shown to fiilly resolve dansyl amino acids [60]. The quantitative determination of enantiomer purity by TLC is possible using densitometry or measurement of fluorescence or UV absorbance followed by the extraction of spots [61]. 

The potential of enantiomer purity determinations by TLC is evident via the separation of diastereoisomeric derivatives. The separation of enantiomers is extensively treated in this book. 

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