Chiral Molecules that Do Not Possess a Chirality Center

18 Chiral Molecules That Do Not Possess a Chirality Center  

A molecule is chiral if it is not superposable on its mirror image. The presence of a tetrahedral atom with four different groups is only one type of chirality center, however. While most of the chiral molecules we shall encounter have chirahty centers, there are otha- stractural attributes that can confer chirality on a molecule. For example, there are compounds that have such large rotational barriers between conformers that individual conformational isomers can be separated and purified, and some of these conformational isomers are stereoisomers. 

Conformational isomers that are stable, isolable compounds are called atropisom. The existence of chiral atropisomers has been exploited to great effect in the development of chiral catalysts for stereoselective reactions. An example is BINAP, shown below in its enantiomeric forms  

Allenes are compounds that also exhibit stereoisomerism. Allenes are molecules that contain the following double-bond sequence  

The planes of the ir bonds of allenes are perpendicular to each other  

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CHIRAL MOLECULES THAT DO NOT POSSESS A CHIRALITY CENTER... 

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