Chemistry Reference
In-Depth Information
pK
a
. In actuality, the pK
a
of m-chlorobenzoic acid is 3.82, thus supporting the con-
clusion of this problem.
6. Arrange the following groups of molecules in order of increasing acidity. Explain your
results using partial charges and inductive effects.
Initially, when considering inductive effects, we realize that F, O, and Cl all possess
partial negative charges. Therefore, we realize that all of these atoms will pull electron
density from the carboxylic acid, thus stabilizing the anion resulting from deprotonation
and lowering the pK
a
values compared to the baseline acetic acid. The question now
focuses on how strong this effect is for each atom. The answer is found in the periodic
table of the elements and relates to electronegativities. Of the three atoms in question, F
is the most electronegative. Moving to the second row, Cl is more electronegative than
O. Since the most acidic compound will have the most electronegative atoms associated
with it, the order of increasing acidity is as follows:
7. Predict pK
a
values for the protons shown in boldface in the following molecules.
Rationalize your answers.
When estimating the pK
a
values for protons adjacent to multiple functional groups, the
pK
a
values can be calculated according to the following formula where n is defined as
the number of relevant functional groups:
