Benzene chirality rule

FIGURE 8. Quadrant projections for application of the benzene sector rule to chiral monosubstituted benzene compounds... 

The benzene sector rule may be nsed to correlate the absolnte configuration of a contiguous chiral cento- of a monosnbstitnted benzene compound with the sign of the CE... 

Based on the CD-spectra of various optically active carbophanes, a sector rule for the correlation of the sign of the 1Lb-Cotton effect of the benzene chromophore with the absolute chiralities of these phanes (as well as for chiral dihydro-9,10-ethano-anthracenes) has been proposed 63). 

Another example for an application of computed sector maps is the OR of phenylalanine, as far as contributions from the phenyl group are concerned [155]. Sector maps for benzene were computed as shown in Fig. 25. The findings of [155] were in agreement with a revised sector rule for the phenyl chromophore by Pescitelli et al. who investigated a set of chiral molecules with phenyl substituents (PhCH(Me)R, with R = Et, "Pr, Pr, and Bu) [265],... 

More numerous, however, are aromatic compounds with an effectively planar n system, the optical activity of which comes from chiral perturbations. Benzene derivatives such as phenylalanine (3) are particularly important. The Lb band of the benzene chromophore (A = 260 nm) is neither magnetically nor electrically allowed. The symmetry selection rule may be broken by vibronic interactions or due to substituents. The interpretation of the observed rotatory strength is not easy, but empirical sector rules have been proposed. (Cf. Charney, 1979 Pickard and Smith, 1990.)... 

When a solution of a racemate (dt) is brought into contact with a crystal built from chiral molecules, d, e.g. lactose, preferential adsorption takes place d may be more readily adsorbed than I or vice-versa again pointing to a difference between d-i> and /-d. A number of racemates have been resolved on columns of lactose. Moeller and Gulyfas (1958) for example, resolved [Co(aca)3]° and [Cr(acac)3]° on lactose hydrate by passing a solution of the complexes in benzene-petroleum through the column. [See also Henderson and Rule (1939), Lecoq (1943), Prelog and Wieland (1944)]. 

Now we can teach also isomerism such as geometric and positional isomers of C2H4, benzene, and chiral isomers, how Nature makes use of cis-trans geometries (retinal. Tamoxifen), and chirality. Mind you, the 3D rules can be applied also to longer chains of hydrocarbons. In brief, we show that molecular architecture can be reconstructed based on a few simple structural elements. 

San Filippo and coworkers (23) have shown that a variety of carboxylic esters are cleaved by KO2 in benzene with crown ether to produce after acidic work-up the corresponding carboxylic acid and alcohol in good to excellent yields (eq. 18). A mechanism involving alkyl-oxygen cleavage was ruled out by stereochemical studies involving esters derived from chiral alcohols. A... 

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