Chiral Molecules with No Centres of Chirality

Extensions of the CIP rules deal with molecules that are chiral as a whole but contain no chiral centres. 

A molecule such as abC=C=Cde is chiral if a b and c d (axial chirality). The additional rule is that near groups precede far groups. 

Apphcation of the axial chirality rule to an allene Near end of axis precedes far chirality is aR. 

Care is needed in some cases e.g., an allene with four different substituents could alternatively be assigned a label using central chirality. To avoid doubt, use the descriptor (f )axiai or aR. 

The application of CIP rules to compounds showing planar chirality is complex because of ambiguities in choosing the correct plane. 

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