Chirality types

Planar chirality is a valuable feature of the ferrocene chemistry (Chart 2B,C) (205). This unnatural chirality type has attracted attention of several groups. Sadeghi and co-workers have demonstrated that the planar chiral ferrocenes are recognized by cytochrome c peroxidase (206). The rate constants for the oxidation of R and S enantiomers by the wild type enzyme equal 2.9 x 106 and 1.6 x 106 M 1 s respectively. Interestingly, the enantioselectivity inverts for the aspartate 34 for lysine mutant and the rate constants become equal to 5.9 x 106 and 14.8 x 106 M-1 s-1, respectively. The discrimination of planar chiral ferrocenes is the case, but the stereoselectivity factors are lower than 3. 

Belsky, V. K., Zorkii, P. M. (1977) Distribution of organic homomolecular crystals by chiral types and structural classes, Acta. Crystallogr. Sect. A, 33A, 1004-1006. 

Fig. 14.3 Representative structures of (a) armchair, (b) zigzag, and (c) chiral type single-walled carbon nanotubes...

In single-wall carbon nanotubes, various chiralities are realized from arm-chair type through zigzag type to chiral type (Figure 2.35), which are known to govern their properties [15]. 

Figure 18 (a) Two dimeric units of the alternating chirality type are necessary to form a closed hexagon ring (b) the resulting planar network motif. 

The examples discussed so far have been for ketones of chirality types commonly encountered. However, similar discriminations are possible with molecules of unusual chiralities, as represented in Scheme 45. 

Several additional chiral type I and III allyl metal reagents based on boron,chromium, and titaniumhave been reported. The most selective of these are the chiral 7-alkoxyallylboronate (231) developed by Wuts for application in a synthesis of (-)-ejco-brevicomin, and the allyltin reagent gener-... 

Chirality type E = enantiomers D - diastereomers. Blocking positions. 

Type I(chiral), Type II(RRSS racemic), or Type in(RS racemic) is mainly determined by the host-guest pairwise interaction. The interaction energy in a single host-guest pair is probably very small. However, it can be amplified or accumulated, in the crystal phase, to a magnitude large enough to alter the intercolumn interaction. 

In this chapter we shall firstly discuss the preparation of optically active polymers starting with type A monomers in enantiomorphic pure form and in racemic form. Then polymerization of chiral type B monomers will be briefly presented and more room will be devoted to asymmetric induction polymerization of nonchiral monomers of this class. Finally we shall mention the stereoregulated copolymerization of chiral monomers with nonchiral analogs which yields macromolecules showing purely conformational optical activity. 

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