Carboxylic Acids
Contents
• Carboxyl group
• Functional derivatives of carboxylic acids
• Acidity of carboxylic acid
Learning
Objectives
At the end of this
lecture, student will be able to
• Identify structure of carboxyl group
• Explain functional derivatives of carboxylic acid
• Explain acidity of carboxylic acids
Carboxylic
Acids
• Carboxyl group → carbonyl group + hydroxyl group
• Functional
derivatives of carboxylic acids
• Functional
derivatives of carboxylic acids
Amide
Acid anhydrides
Ionisation
of Carboxylic Acids
• Carboxylic acids in solution dissociate into carboxylate
ion
• Ka – acidity constant
• Larger the ka → greater the ionization → stronger the acid
Acidity of
Carboxylic Acids
• Carboxylic acids – more acidic than corresponding alcohols
• Example
• Resonance effect
Resonance stabilised acetate ion
• Equivalent resonance structures for acetate ion
• Greater resonance stabilization
• Reduces energy for ionisation
No resonance
stabilization for alcohol and alkoxide ion
• Carboxylic acid yields resonance-stabilized anion,
stronger acid than alcohol
Inductive effect
• Inductive effect of carbonyl group – responsible for
acidity of carboxylic acids
• In both compounds – O—H bond – highly polarized by greater
electronegativity of the oxygen atom
• Carbonyl group – more powerful electron attracting inductive
effect than CH2 group
• Large resonance stabilization of carboxylate ion
• Acidity of a carboxylic acid – due to powerful resonance
stabilization of its anion
• Stabilization and the resulting acidity possible because
of the presence of the carbonyl group
Summary
• Carboxyl group – carbonyl and hydroxyl group
• Functional derivatives of carboxylic acid – acid halide,
ester, amide, acid anhydride
• Acidity of carboxylic acid – acidity constant Ka