Arenes Aromaticity and Antiaromaticity

Aromaticity is extensively discussed in every introductory organic text, and aspects of it were given in Chapter 2, such as the 4 +2 rule. Key features that are diagnostic of an aromatic system include the following  

For neutral 10-electron systems, the story is more complex. Naphthalene is often viewed as a 10-electron system, but really it is better viewed as two six-electron cycles that share an edge. Note that six-electron cycles are especially stable even within the context of aromatic systems. For more complex ring systems, it is generally observed that the larger the number of benzene-like rings, the more stable the structure. 

The aromatic ions cyclopropenyl cation and cyclopentadienyl anion. B. Cyclooctatetraene is nonplanar, but the dianion is planar and aromatic. C. 10 TT electron systems naphthalene, all-cis [lOJannulene, and a possibly planar [lOJannulene with severe transannular interactions. D. A bridged [lOjannulene. E. Dimethyldihydrophenanthrene. 

CHAPTER 14 ADVANCED CONCEPTS IN ELECTRONIC STRUCTURE THEORY 

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