Benzene, as we have seen in this chapter, is the simplest aromatic compound. Pyridine is...

Benzene, as we have seen in this chapter, is the simplest aromatic compound. Pyridine is an analog of benzene in which a CH group is replaced with a nitrogen atom. Pyrimidine is an analog of benzene in which two CH groups are replaced with nitrogen atoms. Each nitrogen-containing compound shows the characteristic reactions of benzene and its derivatives—it is highly unsaturated but does not undergo the characteristic addition reactions of alkenes.

(a) Show by the use of curved arrows that benzene, pyridine, and pyrimidine can be represented as hybrids of two contributing structures.

(b) Show that each aromatic compound has an aromatic sextet—that is, a loop of six electrons within a cyclic system.

(c) Predict the bond angles in pyridine and pyrimidine and the shape of each molecule.