Chapter 30 - Polycyclic Aromatic Compounds with Four or More (usually six-membered) Fused Carbocyclic Ring Systems

Abstract

Publisher Summary Huckel's (4n + 2) rule for aromaticity applies only to planar, monocyclic hydrocarbons, but attempts have been made to extend it to bicyclic and polycyclic compounds. Naphthalene and phenanthrene, and azulene with 10 electrons, are examples of hydrocarbons that are aromatic and conform to the rule. This chapter describes the nomenclature and general physical properties of aromatic polycyclic hydrocarbons on the basis of bond lengths and bond orders, molecular planarity; molecular overcrowding, ultraviolet spectra, nuclear magnetic resonance, diamagnetic susceptibility, resonance energy and proton addition in the formation of complexes and ions. The polycyclic aromatic hydrocarbons are prepared in many instances by methods similar to those used in the synthesis of naphthalene, anthracene and phenanthrene and include the Pschorr ring closure of diazotized amines, the Friedel-Crafts ring closure of arylbutyric acids, and so on. Individual hydrocarbons containing four benzene rings include chrysene and its derivatives, naphthacene, tetracene, benz[b]anthracene; rubrene, benz[a]anthracene, 1,2-benzanthracene, tetraphene, benzanthrenes and their derivatives, pyrene and its derivatives, triphenylene and its derivatives, and pleiadene, benzocyclohepta[de]naphthalene. Hydrocarbons containing five benzene rings comprise of pentacene, lin-dibenzanthracene, benzo[b]naphthacene, pentaphene, 2,3-6,7-dibenzophenanthrene, benzo[a]naphthacene, 1,2-benzotetracene, dibenzanthracenes, benzochrysenes, dibenzophenanthrene, benzopyrenes, perylene and its derivatives, triptycene, and 9,10-dihydro-9,10-o-benzenoanthracene. This chapter also reviews the hydrocarbons containing six or more benzene rings.