Certain compounds with unusually large resonance energies belong to a class of compounds called aromatic compounds. This chapter starts by discussing the criteria a compound must meet in order to be classified as being aromatic. It then discusses some chemical consequences of aromaticity and why aromatic compounds are so stable.
The most frequently encountered aromatic compound is benzene. The chapter concludes by looking at the reactions of benzene. Because of the stability of benzenes aromatic ring, benzene undergoes reactions that are quite different than the reactions that alkenes and dienes (other compounds that have carboncarbon π bonds) undergo.
If a benzene ring has a substituent, the nature of the substituent affects both the reactivity of the benzene ring and the placement of an incoming substituent. This means that you have to pay close attention when you are planning a synthesis so the substituents are placed on the ring in the correct order. Don't worry though, there are lots of problems that give you an opportunity to try your skills.