Acids and Bases - Organic Chemistry Concepts: An EFL Approach - page 86

If there are electronegative groups on the α-carbon, there is an overall -I
effect. The electron withdrawing effect increases the polarity of the O-H
bond and the acidity. Any withdrawal of the negative charge also makes
the carboxylate anion more stable. In other words, the conjugate base
is weaker.

The inductive effect of the R-group of a carboxylic acid also changes the polariza-
tion of the O-H bond in the original carboxylic acid.

Table 6.1 Relative Acidities of Carboxylic Acids
pK a Acid Conjugate Base (Carboxylate) ON of the α -carbon

3.77 -

4.76 −3

2.86 −1

1.29 +1

0.65 +3

Be careful when evaluating the inductive effect. From Chapter 1 you
should remember that the inductive effect occurs through the tightly
held σ bond electrons. Any inductive effect drops off beyond one bond
distance, unless multiple bonding is present to extend the effect
through conjugation. Therefore, if the electron withdrawing groups are
not on the α carbon, they have little or no effect on acidity.