Axial chirality

Axial Chirality - A type of chirality resulting from the distribution of four substituents in two pairs around the chirality axis. Examples of molecules characterized by the presence of chiral axes are allenes (abC = C = Ccd or abC = C = Cab) and atropisomeric ortho-substituted biphenyls. Therefore, the molecular entity can be chiral without the stereogenic center. The configuration then shows the stereodescript Ra and Sa. Specifying an absolute configuration

The absolute configuration is determined by the Cahn-Ingold-Prelog rules. However, they are relaxed, since the substituents are only different at the ends of the axes. A particle instead of four different substituents may therefore contain two pairs of the same. There is also an additional rule: Groups closer to the observer have a higher priority than the other groups. Examples Ra and Sa allen enantiomers (double bonds are not distinguished) with two pairs of substituents X and Y. X is a higher priority substituent. Newman's projection shows a view of the particle observed from the mirror. Dashed lines: blue - mirror, red - chirality axis. The Ra and Sa derivates of the biphenyl derivative (double bonds are not distinguished) have two pairs of substituents X and Y. X is a higher priority substituent. Newman's projection shows a view of the particle observed from the mirror. Dashed lines: blue - mirror, red - chirality axis.

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