Molecules Exhibiting Planar Chirality

All the subsequently shown compounds possess a chirality plane and their helicities can again be described with respect to interposed 4-point figures. In this class belong in the first place so-called ansa-compounds, unsym-metrically substituted cyclophanes, and certain cycloolefin conformations. 

(P)-12-Methyl-14-nitrobi-cyclo[9.2.2]pentadeca-l(13),ll,14-triene New lUPAC-cyclophane name  

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Substituted [2.2]paracyclophane compounds exhibit planar chirality [3, 4]. In contrast to conformationally flexible chiral molecules with an axis of rotation and a rotatable bond around a stereogenic center, the planar chirahty of [2.2]paracyclo-phane compounds possesses a conformationally stable chiral space because of the fixed aromatic rings. From this structural viewpoint, various methods for the optical resolution of planar chiral [2.2]paracyclophanes have been developed since the 1990s [79-92]. In comparison with the establishment of the optical resolution of monosubstituted [2.2]paracyclophanes, there was more scope for the development of optical resolution of pseudo-ortfio-disubstituted [2.2]paracyclophanes [85-92]. Recently, a simple optical resolution method for racemic pseudo-ort/to-dibromo[2.2] paracyclophane rac-38 was reported [93]. As shown in Scheme 11, treatment of rac-38 with a slight excess of n-BuLi and (lR,25,5R)-(-)-menthyl S)-p-toluenesulflnate provided a mixture of diastereomers (Rp,5)-42 and (5p,5)-42. These were readily separated by conventional Si02 column chromatography to afford (Rp,S)-42 and (5p,5)-42 (each in 39 % isolated yield). 

The stereoisomeric relation of the nonplanar D2mirror image. As enantiomers have identical scalar properties (energies, nmr shifts, etc.), but different pseudoscalar properties an experimental differentiation of these chiral molecules is bound to rely on chiral properties, such as optical rotations. The planar E-dimethylbutatriene (5) and Z-dimeth-ylbutatriene (6) exhibit cis-trans isomerism (geometrical isomerism). 5 and 6 differ in their scalar molecular properties. 

Compound 18 exhibits solely a chiral nematic discotic phase (N ) phase because the steric effect of the branched chains at the chiral centre disrupts the ability of the molecules to pack in columns. The large size of the planar aromatic core ensures a high clearing point, but the liquid crystal tendency depends critically on the type of chiral peripheral chain. Hexa-substituted phenylacetylenes were discussed in chapter 3 and exhibited the Np phase. Perhaps not surprisingly, when one of the peripheral acetylene units is chiral, the N phase is exhibited (compound 19). 

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