Special Topic Polycyclic Systems

We needn t stop here. More rings can be attached in fused or bridged fashion to produce wondrously complex stmctures.The naming protocols are complicated, if ultimately logical, and won t be covered here. Many of the compounds have common names that are meant to be evocative of their shapes. Prismane and cubane are examples.The molecular versions of the Platonic solids, tetrahedrane, cubane, and dodecahedrane are all known, although the parent, unsubstituted tetrahedrane stih evades synthesis (Fig. 5.63). 

FIGURE 5.63 Polycyclic natural (cholesterol) and unnatural (the rest) products. 

Spectacular new molecules containing rings are always appearing. In 1984, Professor Kenneth B. Wiberg (b. 1927) of Yale University reported the construction of the polycyclic molecule, tricyclo[1.1.1.0 ]pentane (also known as [l.l.ljpropel-lane. Fig. 5.64), a marvelously exciting molecule. You are now only five chapters into your study of organic chemistry, yet it is possible for you to appreciate why the chemical world was knocked out by this compound. 

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