An Introduction to Delocalized Electrons

We have seen that a carboxylic acid has a value of about 5, whereas the value of an alcohol is about 15. Because a carboxylic acid is a much stronger acid than an alcohol, we know that the conjugate base of a carboxylic acid is considerably more stable than the conjugate base of an alcohol. 

The two structures shown for the conjugate base of the carboxylic acid are called resonance contributors. Neither resonance contributor alone represents the actual structure of the conjugate base. Instead, the actual stmcture—called a resonance hybrid— is a composite of the two resonance contributors. The double-headed arrow between the two resonance contributors is used to indicate that the actual structure is a hybrid. 

Delocalized electrons are shared by more than two atoms. 

the combination of inductive electron withdrawal and the ability of two atoms to share the negative charge makes the conjugate base of the carboxylic acid more stable than the conjugate base of the alcohol. 

Delocalized electrons are very important in organic chemistry—so important that all of Chapter 8 is devoted to them. By that time, you will be thoroughly comfortable with compounds that have only localized electrons, and we can then further explore how to recognize when a compound has delocalized electrons and how delocalized electrons affect the stability, reactivity, and p a values of organic compounds. 

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