Circular dichrogram

Figure 48. Circular dichrogram of the pretzel-shaped molecule 96 in trifluoroethanol.

Figure SO. Circular dichrogram of the cycloenantiomeric [l]rotaxane 100 in trifluoroetha-nol.

The pretzel-shaped molecule 96 (the first pretzelane ) was synthesized by intramolecular bridging of the two sulfonamide units of 79 with a bifunctionalized podand-like chain [54]. Again the enantioseparation of 96 was accomplished with a baseline quality separation and a large separation factor (a=5.20). Preparative separation of the enantiomers enabled the detection of the circular dichrogram of 96 (Figure 48). The optical rotation values of 79 and 96 were both determined to be [aD] = 168° (Troger base [aD] = 281°). 

Again it was surprising that enantioseparation by HPLC was successful because the conformational flexibility of the wheel and the thread entail reduced structural dissymmetry of the enantiomers compared with more rigid molecules. For the rotaxanes 80m and 100 separation factors a were found to be 1.48 and 1.69, respectively. The circular dichrogram of the cycloenantiomeric [ljrotaxane 100 is given in Figure 50. 

Fig. 4.68 Circular dichrograms of dendritically substituted atropines (1) and quinines (2) each of zeroth to second generation (according to Vogtle et al.)...

Collet et al. started chiroptical investigations of (C3)-cyclotriveratrylene The absolute configurations of (C3)-(2H3)-cyclotribenzylene were found to be P-(-l-)-210 and M-(—)-270, respectively. The barrier of the crown-to-crown interconversion was measured as 110.9 kJ/mol. The circular dichrograms of 210a-e were correlated using the exciton optical activity of isotope-substituted representatives (Fig. 79, Table 13). 

We were able to synthesize chiral dendri- rations. In addition, the circular dichrograms mers with stable planar-chiral building blocks clearly indicate that chiral dendrimers based to avoid racemisation. [47] In contrast to the on derivatives of [2.2]paracyclophanes can results of Seebach et al. these dendrimers be employed for complexation of certain show increasing chirality with inreasing gene- metal cations. 

The other maxima do not change. On the other hand in the circular dichrogram several strong Cotton effects appear in part overlapping [55—57] (see Figure 14). 

Fig. 14. Circular dichrograms of a mixture of amylose and Congo red in water (Conditions see Figure...

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