Acids and Bases - Organic Chemistry Concepts: An EFL Approach - page 83

CHAPTER 6
Acids and Bases

6.1 WHY ARE ACIDS AND BASES IMPORTANT?
In organic chemistry, the reactivity of organic acids and bases determines the
reactions of many functional classes of compounds. We understand carboxylic
acids as acidic from their class name. Amines are seen as basic because they are
related to ammonia. This lets us understand the acid-base reactions of these two
functional classes.

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However, it is less easy to connect the broader ideas of acid-base reactions
among other functional classes of compounds. There is a direct relationship
between acidity or basicity and the concepts of electronegativity, bond polar-
ity, inductive effect (Chapter 1), oxidation number (Chapter 2), and resonance
(Chapter 4).

6.2 GENERAL DEFINITIONS
As shown in Figure 6.1 , in the Brønsted-Lowry definition, an acid is any sub-
stance which is a donor of a proton (hydrogen ion, H + ). A base is any substance
which is a proton acceptor. The reaction between an acid and a base is simply a
proton transfer.

The Brønsted-Lowry definition can be used for most of the examples in this
topic.

FIGURE 6.1
Brønsted-Lowry acid-base definition.

The Lewis definition is wider and is not limited to the transfer of a proton. As
shown in Figure 6.2 , an acid is a substance which accepts an electron pair, and a
base donates an electron pair. A proton is a Lewis acid because it accepts an elec-
tron pair into its empty 1 s orbital when it reacts with a Lewis base. The reaction
between an acid and a base gives a Lewis acid/Lewis base complex.