Inherently chiral between

Finally, it should be noted that L is a rotational operator. Therefore, any type of transition that involves exciting an electron between orbitals that are transformed into one another by a rotation (e.g., the n —> n transition of an inherently chiral carbonyl)20,21 will be magnetic dipole allowed and have g > 0.01. 

The use of these asymmetric hydrogenation catalysts gives the C-2 chiral center in about 80% optical purity. The same value would apply also to the chiral methyl. For further purification, a crystallization process was used. The optically impure lactic acid (an oil) was dissolved in an approximately equal volume of boiling diethylether diisopropyl ether, 1 1 on standing at 5°C large, colorless, crystals of optically pure chiral methyl chiral lactic acid, 162, were deposited. The recovery of the purified material was 60%. Because of the inherent relationship between the two chiral centers, optical purity at C-2 guarantees optical purity at C-3. 

The possible number of inherently chiral structures and conformers further increases if the calixarene contains both different phenolic units and different bridges in the macrocyclic skeleton. For example, two chiral monoethers 88a,b are available from dihomooxacalix[4]arenes (one -CH2-0-CH2- bridge instead of -CH2-).17188b is the preferred product of the mono-O-alkylation, since the negative charge of the respective phenoxide anion is better stabilized by intramolecular hydrogen bonds due to the smaller distance between the phenoxide anion and the hydroxy groups. Tetraketone derivatives (Y = CH,-C(0)-R) in the two possible partial cone conformations, have been prepared in moderate yields. 

In chiral vinylcyclopropanes the chromophore can be viewed as inherently chiral, i.e. all the electronic transitions have simultaneously an electric (/i) and a magnetic (m) transition moment. For transoid or cisoid (indicated in broken lines below) arrangements the magnetic moments are generated by a circular displacement of electric charge density around the bond between the cyclopropane and the ethylenic moieties. The helical movement of electron density involves essentially p-atomic orbitals twisted relative to each... 

If the very minute parity breaking effects of weak interactions between elementary particles are disregarded, natural optical activity is due entirely to the inherent chirality of the sample. A sample is chiral if it is not super-imposable onto its mirror image. Chiral objects are also referred to as dissymmetric. Isotropic solutions only are chiral if the individual molecules are chiral. 

An obvious instance where the driving force is not a determining factor is in the reaction of chiral mediators. The inherent chirality of proteins implies that they should exhibit chiral discrimination between enantiomers and this has been widely exploited in the selective transformation of one enantiomer in a racemic mixture by enzymes. 

Of substantial interest were the chiroptical properties of these enantiomeric 60 derivatives with chiral functionalization patterns the mirror-image CD spectra of ( C)-2 and ( A)-2 displayed large Cotton effects between 250 and 750 nm with Ae values approaching 150 cm mmoL [25, 59]. These intensities of the CD bands are of similar magnitude to those measured for inherently chiral fullerenes (such as D2-C76 [78] and their derivatives [79]) but are much larger than those measured for non-racemic fullerene derivatives in which the chirality only results from the addends [25]. 

A singular chiral adduct was formed between C70 and two RujfCOjg units which are known for the complexation of arenes. From the corresponding mono -adduct it was known that the trinuclear ruthenium moieties add preferentially to the hexagons of highest local curvature [143]. Assuming addition of two Ru3(CO)9 units at opposite poles, three constitutional isomers of [[Ru3(CO)9 2(ft-T2, /2, rf-C7o)] are possible in analogy to the addition of achiral divalent addends to a-type bonds (cf. Sect. 4.2.1) [54,131 ] One of them has symmetry and two have C2-symmetry. Of the three formed isomers, the major one afforded crystals suitable for X-ray analysis it has an inherently chiral addition pattern and corresponds to structure ( )-59 [143] (Fig. 9). 

NMR and temperature rising elution fractionatiOTi (TREF) polymer characterization data, on the other hand, pointed to a direct effect of Lewis bases on site enantioselectivity in fact, the highly isotactic polymer fraction yielded by catalysts modified with Lewis bases is not only much more abundant, but also more stereoregular compared with that of Lewis-base-free systems, while keeping the typical fingerprint of enantiomorphic-site control [42]. This suggests that Lewis base molecules are in nonbonded contact with the inherently chiral catalytic species, and shape their active pocket to make them better able to discriminate between the two enantiofaces of propene at the insertion step. 

Platinum(ii)-containing complexes with inherently chiral binaphthol derivatives display a versatile scaffold between random coils and singleturn helical strands, in which the conformational transition is controlled by the Pt... Pt and n-n interactions of allq7nylplatinum(ii) terpyridine moiety upon solvent and temperature modulation. ... 

Bridges between aromatic rings of calixarenes and resorcinarenes are commonly considered chemically inert. Therefore, substitution of the bridges is the least common among modifications due to synthetic difficulties. However, in some cases, the modifications can be introduced prior to the cyclization step, as in 49 (Fig. 2.13) [55, 56]. Another possibility involves using thiacalixarenes. Oxidation of the adjacent sulfide functional groups in an a/ifi-relationship leads to an inherently chiral structure 50 [57]. It should be noted however, that inherent chirality in this case is inextricably boimd to stereogenic centers at the sulfur atoms. 

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