Some molecules have a molecular skeleton which is inherently chiral (helical), one such case being hexahelicene. One face of this extended aromatic molecule must lie above the other due to steric crowding. To view the situation, select the show clash option in the model window below. Note that for hexahelicene to be planar, the red carbon atoms would have to be in the same place. Choose Atoms 100% to visualise the steric interactions involved as the molecule extends.

The structure of hexahelicene
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