Acidity of Substituted Benzoic Acids : Electron-donating groups
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LibreTexts Project
الجزء والصفحة:
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16-10-2019
1959
Acidity of Substituted Benzoic Acids : Electron-donating groups
The conjugate base of benzoic acid is destabilized by electron-donating groups. This makes the acid less acidic
Electron-donating groups activate the benzene ring to electrophilic attack and make benzoic acids less acidic.
Notice the trend in the following table where electron donating substituents (X) at the para position lead to weaker acids while those having more electron withdrawing groups, further down the table, generate stronger acids.
|
Dissociation Constants of p-Substituted Benzoic Acid
|
|
X
|
pKa
|
|
|
—N(CH3)2
|
6.03
|
|
|
—NHCH3
|
5.04
|
|
—OH
|
4.57
|
|
—OCH3
|
4.50
|
|
—C(CH3)3
|
4.38
|
|
—H
|
4.20
|
|
—Cl
|
4.00
|
|
—Br
|
3.96
|
|
—CHO
|
3.77
|
|
—CN
|
3.55
|
|
—NO2
|
3.43
|
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