Page 135 - Mechanism and Theory in Organic Chemistry

Chapter 3

ACIDS AND

BASES

3.1 BRQINSTED ACIDS AND BASES
Of the concepts that chemists use to make sense of chemical transformations,
ideas about acids and bases are among the most fruitful. Nearly all of the hetero-
lytic reactions that we shall be considering can be thought of as acid-base pro-
cesses; it is therefore appropriate to begin our discussion of the chemical proper-
ties of organic compounds with a review of these ideas and of their applications in
organic chemistry.

Definition of Brensted Acids and Bases
Acids and bases have been known for centuries, but the definitions in common use
today are of comparatively recent origin. In 1923 J. N. Bransted proposed the
following definitions :l
AarmkKGa proton donor.
A base is a proton acceptor.
An acid HA is thus any substance that reacts according to Equation 3.1, and
a base B is any substance that reacts according to Equation 3.2:
HA ---t H+ + A- (3.1)

If one confines one's attption to the liquid phase, however, these idealized re-
actions apparently never occur. The proton, H+, does not exist free in solution,

J. N. Brnnsted, Rec. Trav. Chim., 42, 718 (1923).