Organic Chemistry

benzene cyclohexane

A

s you continue your study of organic chemistry, you will

notice that the concept of having delocalized electrons is

invoked frequently to explain the behavior of organic

compounds. For example, in Chapter 8 you will see that having

delocalized electrons causes certain dienes to form products that

would not be expected on the basis of what you have learned about electrophilic addi-

tion reactions in Chapters 3–6. Electron delocalization is such an important concept

that this entire chapter is devoted to it.

Electrons that are restricted to a particular region are called localized electrons.

Localized electrons either belong to a single atom or are confined to a bond between

two atoms.

Not all electrons are confined to a single atom or bond. Many organic compounds

contain delocalizedelectrons. Delocalized electronsneither belong to a single atom

nor are confined to a bond between two atoms, but are shared by three or more atoms.

You were first introduced to delocalized electrons in Section 1.19, where you saw that

the two electrons represented by the bond of the group are shared by three

atoms—the carbon and both oxygen atoms. The dashed lines indicate that the two

electrons are delocalized over three atoms.

In this chapter, you will learn to recognize compounds that contain delocalized

electrons and to draw structures that represent the electron distribution in molecules

O

δ–

O

δ–

delocalized

electrons

CH 3 C

p COO-

localized electrons

CH 3 NH 2

localized electrons

CH 3 CH CH 2

7

Electron Delocalization

and Resonance •

More About Molecular

Orbital Theory

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