We saw in Section 13.8 that benzene can be represented by...

We saw in Section 13.8 that benzene can be represented by either of two resonance forms, which differ in the positions of the double bonds in the aromatic ring. Naphthalene, a polycyclic aromatic compound, can be represented by three forms with different double-bond positions. Draw all three structures, showing the double bonds in each (the following numbered skeletal structure of naphthalene shows only the connections among atoms).

Key Concepts

Resonance

Resonance is a concept in chemistry used to describe the delocalization of electrons within molecules that cannot be accurately represented by a single Lewis structure. Instead, multiple contributing structures are drawn to illustrate different possible distributions of electrons. The actual electronic structure is a hybrid of these forms, which helps explain molecular stability and reactivity that cannot be captured by any single resonance form.

Aromaticity

Aromaticity refers to a property of cyclic, planar molecules that possess a conjugated system of p orbitals leading to unusual stability. This stability arises from the delocalization of ?-electrons over the entire ring structure. Benzene is the prototypical aromatic compound, and aromatic character is an essential feature in describing the behavior and reactivity of many organic compounds including polycyclic systems like naphthalene.

Polycyclic Aromatic Compounds

Polycyclic aromatic compounds consist of multiple fused aromatic rings, leading to extended conjugated systems. These compounds, such as naphthalene, exhibit resonance stabilization where multiple resonance structures can be drawn. The existence of several resonance forms with different arrangements of double bonds reflects the complex electron delocalization across the multiple rings, which is key to understanding their chemical properties.

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