Learning Objectives After you have completed Chapter 2, you should be able to fulfillall of the detailed objectives listed under each individual section. use the information presented in this chapter, along with material from earlier chapters, to solve problems, particularly road-map problems and those requiring an understanding of spectroscopy. explain the concept of aromaticity and the stability of aromatic compounds. define, and use in context, the key terms introduced. In Chapter 1, we identified an aromatic compound as being a compound which contains a benzene ring (or phenyl group). It is now time to define aromaticity in a more sophisticated manner. In this chapter, we discuss the stability of benzene and other aromatic compounds, explaining it in terms of resonance and molecular orbital theory. You will study the nomenclature of aromatic compounds and the Hückel (4 n + 2) rule for predicting aromaticity. The chapter concludes with a brief summary of the spectroscopic properties of arenes. 2.1: Introduction Aromatic hydrocarbons contain ring structures with delocalized pi electron systems and are more stable than their saturated analogs. 2.2: Naming Aromatic Compounds 2.3: Structure and Stability of Benzene 2.4: Aromaticity and the Hückel 4n + 2 Rule In 1931, German chemist and physicist Erich Hückel proposed a theory to help determine if a planar ring molecule would have aromatic properties. His rule states that if a cyclic, planar molecule has 4n+2 π electrons, it is considered aromatic. This rule would come to be known as Hückel's Rule. 2.5: Aromatic Ions Carbanions and carbocations may also show aromatic stabilization. 2.6: Aromatic Heterocycles 2.7: Polycyclic Aromatic Compounds 2.8: Reactions at the Benzylic Position 2.9: Spectroscopy of Aromatic Compounds 2.10: Additional Problems 2.S: Benzene and Aromaticity (Summary)