Chirality, cause

On the basis of the above result, the class 4 of chiral porphyrin complex (18) possessing a chiral strap, and facial chirality caused by it, has been introduced.66,67 Epoxidation with the complex (18) in the presence of 1,5-dicycohexylimidazole, which blocks the nonbridged side of the complex, shows good to high enantioselectivity when the substrates are conjugated mono- and m-di-substituted olefins (Scheme 11). 

The stereochemical situation in these experiments may be more involved than one would anticipate at first sight. Buck et al. have succeeded in resolving (83). These enantiomers can only be the result of axial chirality caused by a torsional barrier to rotation about the aromatic-carbonyl bond being high enough to freeze the amide groups out of plane in the pyridinium salt. 

Molecules that are not chiral cause no difference in velocity of the two circularly-polarized beams hence there is no rotahon of the plane of polarized hght described by their vector sum. Achiral molecules, therefore, are not ophcahy active. 

Tilted smectic mesophases formed by chiral materials are designated by the superscript. For instance, when the molecules of the SmC phase are chiral the phase is called SmC. In SmC the phase structure is basically the same except that the molecular chirality causes a minor and gradual change in the direction of the molecular tilt. However, no change in the tilt angle with respect to the layer normal occurs in SmC. This change in tilt direction from layer to layer gradually describes a helix [38],... 

It is clear that uncompensated chemical (configurational) chirality causes lamellar twist manifested as banded polymer spherulites. A particular enantiomer of a particular chiral polymer almost always has lamellar twist of one hand only, but R enantiomers of different... 

In certain crystals, e.g. in quartz, there is chirality in the crystal structure. Molecular chirality is possible in compounds which have no chiral carbon atoms and yet possess non-superimposable mirror image structures. Restricted rotation about the C=C = C bonds in an allene abC = C = Cba causes chirality and the existence of two optically active forms (i)... 

Whal causes oplical rolalion" The plane of polanzalion of a lighl wave undergoes a minute rolalion when il encounters a chiral molecule Enanliomenc forms of a chiral molecule cause a rolalion of Ihe plane of polarizalion m exaclly equal amounls bul m... 

Disubstituted cyclohexanes present us with a challenging exercise in stereochemistry Con sider the seven possible dichlorocyclohexanes 1 1 as and trans 1 2 as and trans 1 3 and as and trans 1 4 Which are chiral Which are achiral Four isomers—the ones that are achiral be cause they have a plane of symmetry—are relatively easy to identify... 

In most cases, the proteia is immobilized onto y-aminopropyl sUica and covalently attached usiag a cross-linking reagent such as -carbonyl diimidazole. The tertiary stmcture or three dimensional organization of proteias are thought to be important for their activity and chiral recognition. Therefore, mobile phase conditions that cause proteia "deaaturatioa" or loss of tertiary stmcture must be avoided. 

A synthesis of optically active citroneUal uses myrcene (7), which is produced from P-piaene. Reaction of diethylamine with myrcene gives A/,A/-diethylgeranyl- and nerylamines. Treatment of the aHyUc amines with a homogeneous chiral rhodium catalyst causes isomerization and also induces asymmetry to give the chiral enamines, which can be readily hydrolyzed to (+)-citroneUal (151). 

It is possible to obtain pure enantiomers of chiral compounds. One property of separated enantiomers is to cause the rotation of the plane of polarized light by opposite... 

What causes optical rotation The plane of polarization of a light wave undergoes a minute rotation when it encounters a chiral molecule. Enantiomeric forms of a chiral molecule cause a rotation of the plane of polarization in exactly equal fflnounts but in... 

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