18. Aromaticity

The following molecules and ions are grouped by similar structures. Classify each as aromatic, antiaromatic, or nonaromatic. For the aromatic and antiaromatic species, give the number of pi electrons in the ring.

(d)

The following molecules and ions are grouped by similar structures. Classify each as aromatic, antiaromatic, or nonaromatic. For the aromatic and antiaromatic species, give the number of pi electrons in the ring.

(g)

Hexahelicene seems a poor candidate for optical activity because all its carbon atoms are sp² hybrids and presumably flat. Nevertheless, hexahelicene has been synthesized and separated into enantiomers. Its optical rotation is enormous: [α]_D = 3700°. Explain why hexahelicene is optically active, and speculate as to why the rotation is so large.