Enantiomers three-dimensional representations

FIGURE 25 1 Three dimensional representations and Fischer projections of the enantiomers of glycer aldehyde... 

Fig. 21 Three-dimensional representation of a ternary system of two enantiomers in a solvent, S. One of the faces of the prism (at left) corresponds to the binary diagram of D and L (here a conglomerate). Shaded area isothermal section representing the solubility diagram at temperature T0. (Reproduced with permission of the copyright owner, John Wiley and Sons, Inc., New York, from Ref. 141, p. 169.)...

Figure 1.26. Double Bingel addition to C70 leads to an achiral top) and two inherently chiral (center and bottom) addition patterns. Combination of each of the latter with chiral ester moieties affords two diastereoisomeric pairs of enantiomers. The enantiomers of each pair were prepared separately by addition of either (R,R) or (S, -configured malonates to C70, and all stereoisomers were isolated in pure state. The black dots mark intersections of the C2-symmetry axis with the [70]fullerene spheroid. Next to the three-dimensional representations, constitution and configuration of the addition patterns are shown schematically in a Newman type projection along the Cs-axis of C70. Of the two concentric five-membered rings, the inner one corresponds to the polar pentagon closest to the viewer, and the attached vertical line represents the bond C(l)-C(2) where the first addition occurred. The functionalized bonds at the distal pole depart radially from the outer pentagon.

There are two (and only two) distinct three-dimensional representations for lactic acid enantiomers (see the figure on page 21) they are... 

The (+) enantiomer of the inhalation anesthetic desflurane (CF3CHFOCHF2) has the S configuration. Draw a three-dimensional representation of (S)-(4-)-desflurane. 

There are times when a three-dimensional representation is important, hut the subject is a racemic mixture of the two enantiomers rather than one enantiomer. Unless both enantiomers are drawn, the figure appears to focus only on a single enantiomer. Our molecule, 3-methylhexane, illustrates this point in Figure 4.16. If we are talking about a racemic mixmre of 3-methylhexane but want to show the three-dimensional structure of this molecule, we should, stricdy speaking, draw both of the enantiomers. In practice this is rarely done, and you must be alert for the problem. Unless optical activity is specifically indicated, it is usually the racemate that is meant. 

Figure 2.1 Ic and d show three-dimensional representations of the two enantiomers orientated to emphasize that they are reflections of one another. If you have a modelling kit you should construct models of the two enantiomers shown in Figure 2.11c and d and confirm that they cannot be superimposed on one another.

PROBLEM 24.13 Draw tetrahedral representations of the two glyceraldehyde enantiomers using wedged, dashed, and normal lines to show three-dimensionality. 

FIGURE 6 Graphical representation of the guest-host diastereoisomeric complex formation (a) in the presence of acid in the mobile phase and (b) in the absence of acid in the mobile phase, (c) Three-dimensional structures of the guest-host complexes formed between R- and 5-enantiomers of a-phenylethylamine and chiral 18-crown-6 ether CSP. 

Chiral stationary phases (CSPs) developed on the basis of the strategy devised by Pirkle et al. (Pirkle 1980, 1984, 1988, 1992 Wolf 2002) depend on an explicit recognition of the three-dimensional fit between the CSP molecule and the enantiomers of the analyte. This strategy is based on Piride s Principle of Reciprocity (Figure 4.14), namely, that a single enantiomer of a racemate which separates well on one CSP will, when used to produce a second CSP, usually afford separation of the enantiomers of analytes that are structurally similar to the chiral selector of the first CSP. Figure 4.14 also shows two chiral selectors that do exhibit reciprocity, as well as a representation of how the specific interaction between the (S)-form of the first CSP can select for one enantiomer of the second. This is a typical example of the Pirkle-type chiral selectivity. 

Now that we know what enantiomers are, we can think about how to represent their three-dimensional structures on a two-dimensional page. Let us take one of the enantiomers of 2-butanol as an example. Following are four different representations of this enantiomer ... 

It is worthwhile to notice that there are several different ways to represent the three-dimensional structure of chiral molecules on a two-dimensional page. For example, following are four different representations of one enantiomer of 2-butanol. 

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