Order chiral

One may use the stronger term chirality discrimination when a substantial suppression of one intermolecular diastereomer with respect to the other occurs. This requires multiple strong interactions between the two molecular units and therefore more than simple monofunctional alcohols. Some examples where one of the molecules involved is a chiral alkanol are reported in Refs. 112 and 119 121. Pronounced cases of higher-order chirality discrimination have been observed in clusters of hydroxy esters such as methyl lactate tetramers [122] and in protonated serine octamers [15,123,124]. The presence of an alcohol functionality appears to be favorable for accentuated chirality discrimination phenomena even in these complex systems [113,123,125,126]. Because the border between chirality recognition and discrimination is quite undefined, it is suggested that the two may be used synonymously whenever both molecular partners are permanently chiral [127]. 

Krai has recently reported a related system in which porphyrins bearing bicyclic guanidine substituents (such as the tetra-substituted species 70 shown is Scheme 35) form highly ordered chiral assemblies in aqueous solution [92]. 

Liquid-Crystalline Solvents as Mechanistic Probes The Properties of Ordered Chiral Media That Influence Thermal and Photochemical Atropisomeric Interconversions of l,l -Binaphthyl... 

Intermolecular [2+2] photocycloaddition has been applied to the synthesis of a wide variety of natural products and their analogs, which frequently contain four-membered rings in highly ordered chiral environments, or a structure which can be readily derived from the [2+2] cycloadduct. The marine natural product Spatol (57) contains a three fused ring system (see Scheme 16). This has been... 

A more efficient process is one in which the chiral auxiliary, although still used stoichiometrically, can be recovered and reused. A notable example of a second order chiral reagent is ester (204 equation 122). In this process, methyl mandelate is converted into chiral ester (204). After the aldol reaction, the product (205) is saponified and the chiral auxiliary may, in principle, be fully recovered and recycled. However, in practice, yields are never quantitative and the overall efficiency of auxiliary recovery is usually of the order of 50%. 

Fig. 20 Representation of geometrically ordered chiral blocks distributed randomly through the silica wall and bounded chromophores. Jin et at. Copyright 2012 John Wiley and Sons.

Under just the right conditions, a mixture of a highly polar liquid, a slightly polar liquid, and an amphiphilic molecule form micelles that are not spherical. They can be rodlike, disc-like, or biaxial (all three axes of the micelles are different). These anisotropic micelles sometimes order in the solvent just as liquid crystal molecules order in thermotropic phases. There is a nematic phase of rod-shaped micelles, another nematic phase of disc-shaped micelles, and even a biaxial nematic phase, in which the molecular axes transverse to the long molecular axis partially order. Chiral versions of these phases with the same structure as the chiral nematic phase also form. 

Selective images are produced by the detection of half the incident wavelength due to the occurrence of second harmonic generation by weU-ordered chiral crystals Fluorescence resonance energy transfer (FRET)... 

Zalar B, Gregorovic A, Blinc R (2000) Interlayer molecular exchange in an anticlinically ordered chiral liquid crystal. Phys Rev E 62 R37-R40... 

Very interestingly, when these subunits were mixed in water, helical superstructures (Figure 7(c), thicknesses 14-28 nm, widths 30-50 nm, pitches 180-430 nm) were immediately formed (association constant 1.13 x 10 Af ) [50]. These helical structures are typical to the ordered chiral bilayer membranes [51], and are distinct from the aggregate morphology observed for the individual subunits. The observed helical assembly showed blue-shifted absorption of the azobenzene chromophore at 332 nm, with an exciton coupling in circular dichroism. These observations clearly... 

This section pertains to reports on oriented molecules in which phases other than the usual thermotropic nematics have been used. Studies in chiral, smectic, columnar, lyotropic and polymeric liquid crystals as well as other unusual phases have been presented. The use of carbon-proton heteronuclear selective refocusing 2D NMR experiment designed for the spectral analysis of enantiomers dissolved in weakly ordering chiral liquid crystal solvents has been proposed." The method permits the extraction of carbon-proton residual dipolar couplings for each enantiomer from a complex or unresolved proton-coupled... 

The uses of optically active co-monomers (5)-(+)-MCPS and (S)-(-)-MCPP as holes transport side-chain and 9-phenylcarbazole derivatives (S)-(h-)-MOSI, (5)-MAP-A and (S)-MAP-C as electro-optic side-chain known today. The dipolar interactions between chromophores and an ordered chiral confirmation of prevailing helical hardness are characterized by thermally and spectroscopic method. 

Chirality is given in the following order chirality of bisphosphine ligand followed by planar chirality of carborane cluster. 

This cooperative effect, depending on comonomer structure and polymer stereoregularity, can be transmitted for long chain sections, a small amount of chiral comonomer being sufficient to induce chirality of one single type in the whole macromolecule. This effect can be of great interest for the simple and economical synthesis from commercial achiral monomers and a small amount of chiral comonomers of functional optically active copolymers with an ordered chiral secondary structure to be used as reagents or catalysts for asymmetric synthesis. 

Internally, GEMINI uses a rich set of data types with well-defined relationships which can include redundancy or ambiguity. Such information includes atomic number, connectivity, bond order, chirality, charge, co-ordinates, etc. Fortunately, there are very few different representations that are used for each kind of information, and algorithms are readily available for their interconversion. 

The optical properties of the nanofibers are highlighted by the fact that when the crystals in aqueous suspension reach a specific concentration, they tend to form an ordered chiral nematic phase. Above this critical concentration aqneons suspensions present birefringence characteristics [42], This feature was observed by authors such as Siqueira et al. [63] and Viet et al. [82] in the CNCs obtained from golden grass (capim donrado) and cotton fibers, respectively. In Figure 13.9 it is possible to observe the birefringence characteristics of these cellulose whiskers suspensions obtained from the literature. 

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